Speech Errors,
Speech Production Models, and Speech Pathology
Copyright
Notice: This material was written
and published in Wales by Derek J. Smith (Chartered Engineer). It forms part of
a multifile e-learning resource, and subject only to acknowledging Derek J.
Smith's rights under international copyright law to be identified as author may
be freely downloaded and printed off in single complete copies solely for the
purposes of private study and/or review. Commercial exploitation rights are
reserved. The remote hyperlinks have been selected for the academic appropriacy
of their contents; they were free of offensive and litigious content when
selected, and will be periodically checked to have remained so. Copyright ©
2003-2018, Derek J. Smith.
First published 08:00 GMT 29th October 2003; this version
[2.0 - copyright] 11:00 BST 9th July 2018.
Some of this
material appeared in Smith (1997).
It has here been considerably expanded and supported with hyperlinks. Speech
and Language Therapy students will probably benefit from refreshing their
memories on the difference between segmental and suprasegmental
phonology [glossary]
before proceeding.
When the language
production system is working correctly, it is easy to underestimate its
complexity. Every now and then, however, the system slips up and produces an
error, and errors in any system can have a tremendous explanatory value. They
can tell us, for example, whether apparently separate functions fail separately
or together, and thus whether they probably derive from one or more modular
processes. With further analysis, they can also tell us which modules
communicate with which other modules, what form of encoding is being passed
back and forth, and how well protected the communication links are against
damage or interference. In this section, we look at the commonest types of
everyday speech error.
1.1 Slips of
the Tongue
In an early study of the sort of errors we all make in our everyday speech, Boomer and Laver (1968) judged that the phrase was one of the main units of speech production. They based this judgement on the empirical observation that errors rarely transcended phrase boundaries. Boomer and Laver's study prompted a wave of interest in this topic area, and culminated in some powerful new theories. Error corpus data was used, for example, by Gary S. Dell of the Beckman Institute, University of Illinois, to develop his "Spreading Activation Theory" of lexical access [to be discussed in detail in Section 3.1]. Dell (1986) identifies three levels of slip of the tongue error, as follows .....
(a) Sound Errors: These are
accidental interchanges of sounds between words. Thus "snow flurries"
might become "flow snurries". (Boomer and
Laver had already claimed that segmental errors such as these account
for about 60% of all errors.)
(b) Morpheme Errors: These are
accidental interchanges of morphemes between words. Thus "self-destruct
instruction" might become "self-instruct destruction".
(c) Word Errors: These are
accidental transpositions of words. Thus "Writing a letter to my
mother" might become "Writing a mother to my letter".
Additionally, each of these three levels of error may take various forms .....
(b) Perseverations: Where a later
output item is corrupted by an element belonging to an earlier one. Thus
"waking rabbits" - "waking wabbits".
(c) Deletions: Where an output
element is somehow totally lost. Thus "same state" - "same sate".
Dell then points out that there is a clear same-category pattern to most error occurrences. Thus initial consonants will interact predominantly with other initial consonants, prefixes with other prefixes, and nouns with nouns. This is consistent with verbal storage and retrieval processes also being organised on some sort of same-category basis. Dell also points to the phenomenon of "accommodation", the fact that an error at an early output stage can nevertheless proceed quite happily through all the remaining output stages, without detection, and with subsequent syntactic and morphological changes being correctly but incongruously applied.
|
Exercise 1 -
Speech Errors 1 Block copy the immediately
preceding paragraph into a temporary word processing file, and edit it to
contain examples of the following types of error ..... Anticipation, perseveration, transposition, and deletion of a
sound; Anticipation, perseveration, transposition, and deletion of a
morpheme; Word transpositions within a clause; Word transpositions between
adjacent clauses; Word transpositions between non-adjacent clauses; Word
transpositions between adjacent sentences; Word transpositions between
non-adjacent sentences. 2 Read the resulting text out loud. Which types of error are unlikely, in your judgement, to happen in practice? Why? Do you agree with Boomer and Laver's observation that errors typically take place within clauses, not between them? |
MIT's Stephanie Shattuck-Hufnagel has focussed on the role of word-onset consonants in speech production planning (Shattuck-Hufnagel, 1987). She found that what she called "sublexical" errors - speech errors in the delivery of an otherwise properly selected real word - tended mainly to affect word-onset consonants. She explained this using a "slot-and-filler" model of word construction, in which there is proposed a separate representation of (a) segments (or "fillers"), and (b) a framework (or "frame") of "slots" to lock those segments into position. The full model runs as follows .....
"Step 1. Selection of a set of candidate open class or
content words from the lexicon [glossary
- note that there are two substantially different usages of this word, and that
Shattuck-Hufnagel here appears to be using the
psycholinguistic one - Ed.]. Selection can be accomplished by
transferring lexical items to a short-term processing store, or by marking
their lexical representations temporarily [see NB below]. These candidate
lexical items provide the set of phonemic segments among which final selection
for the utterance will be made, and among which interaction errors can occur.
The form of each lexical item specifies its segments and their serial
order. Step 2. Construction of
syllabic structure and other apparatus for associating main lexical stress to
the open class lexical items.
These processes incorporate the rest of the word minus the onset; word onset
consonants are ignored until later. Step 3. Transfer
or association of the non-onset portions of content morphemes, now organised
into the metrical structures that govern lexical stress, to the emerging
phrasal framework. While the hierarchical structure of the phrasal frames that
receive the non-onset portions of the content words is not fully specified in
this model, we propose that among other things they define two classes of
components for open class items: word onset locations (which at this point in
the processing remain empty), and locations for the rest of each word (which
have now been filled). These two structural components are present for every
content word in the phrasal frame, even for vowel-initial words whose
word-onset consonant component will not be filled. Step 4.
Eventual transfer or association of word-onset consonants
into the word-onset locations for content words in the phrasal frame.
All segments of the content words of the phrase are now in place. Step 5. Transformation of this representation with its
accompanying hierarchical organisation into a complete string of discrete fully
specified segmental elements, including those of grammatical morphemes, and
subsequently into a pattern of motor commands characterised by substantial
temporal overlap in the effects of adjacent segments. This process presumably
involves many steps, among them one that is subject to single-segment errors at
any position in the word. The influence of suprasegmental
structure on interaction errors at this point in the processing is not clear,
but non-interaction errors, which are distributed more evenly across word
positions, may occur here." (Shattuck-Hufnagel,
1987, p47; bold emphasis added)
1.2 Spoonerisms
An interesting subtype of sound errors is the "Spoonerism". Spoonerisms are an often amusing cluster of word-initial transposition errors, and are named after the Oxford academic, the Reverend W.A. Spooner (1844-1930), in whom the affliction - it is safe to believe - occurred naturally (at least to begin with). Here are some examples of Spooner's own isms .....
Two qualities distinguish Spoonerisms from ordinary sound errors. The first is that the sound transposition generates two proper words, and the second is that the two new words themselves make some different sense together. However, close study of the natural history of the phenomenon raises other interesting observations. Here is an early sceptic, who clearly believed that Spooner was milking his defect for all it was worth .....
"Curiously
enough the Spoonerism is named after a man who rarely made Spoonerisms as
dictionaries define them. A recent study [Robbins (1966)] indicates that
Spooner's Spoonerisms were rather carefully planned - high level humour rather
than unintentional error ....." (Mackay, 1970, p323)
Mackay analysed previously published lists of Spoonerisms, carefully rejecting any which could be judged as intentionally humorous or otherwise spurious. Detailed analysis of the 179 examples which remained drew him to a number of conclusions concerning the likely units of speech production. Here are Mackay's specific observations .....
"1.
Repeated phonemes usually occurred before and after the reversed phonemes. 2.
Reversals before repeated phonemes were as common as reversals after repeated
phonemes, contradicting chain association theories. 3. The syllabic position of
reversed phonemes was almost invariably identical, indicating that syllables must be a unit
in speech production. 4. Consonants in the initial position of syllables were
more frequently reversed than would be expected by chance [.....] 5.
Significantly more reversals involved the initial phoneme of words than would
be expected by chance, indicating a lexical factor in Spoonerisms. 6.
Distinctive features of reversed phonemes were usually similar except for place
of articulation [.....]. This suggested the possibility of two distinct types
of mechanism in speech production: one for Form of Articulation, including
voicing, nasality, and openness, and another for Place of Articulation. 7.
Consonants were more frequently transposed than vowels. 8. Reversed phonemes
occurred closer together in words and sentences than could be expected by
chance. 9. [.....] Spoonerisms in German and English were shown to be
quantitatively similar [as were] Spoonerisms in Latin, Croatian, Greek, and
French, suggesting that phoneme reversals may result from universal underlying
mechanisms common to all speakers. 10. No support was found for chain
association explanations of Spoonerisms ....." (Mackay, 1970, p347)
Mackay then suggested the existence of some sort of "buffer system", that is to say, a temporary memory store situated part-way down the motor hierarchy [remind me of this] and working on a "store-and-forward" basis.
ASIDE: This usage of the term
"buffer" evolved in computer science, where it allows a sending
module and a receiving module to work at slightly different speeds if
necessary. Output from the sending module is passed to the buffer store at a
speed the sending module finds convenient, and read from the buffer store by
the receiving module at a speed the receiving module finds convenient. Since
minor processing delays can now be absorbed within the individual modules, the
operation of the system as a whole can, for a small investment in the
intervening resource, be significantly improved.
Here is how Mackay saw the mental buffer system operating .....
"In
the present study the reversed phonemes always originated in the same phrase,
which further suggests that the buffer system displays no more than one phrase
at a time. The syllable must be another unit since reversed phonemes tend to
maintain the same syllabic position. However [.....] the fact that in
Spoonerisms a unit smaller than the syllable crosses syllable boundaries,
suggests the existence of smaller units. The question now arises as to whether
phonemes are a unit in this hierarchy. [.....] Another set of questions relates
to the buffer system. How much is specified in the buffer system? In the
present model, for example, duration of phonemes is left unspecified, but
phonemes, syllables, and stress are marked. In what form are the units in the
buffer specified? Are articulatory goals or targets represented in the buffer
rather than phonemes? Is stress independent of the elements that are stressed?
How are syllables coded - in abstract form independent of the phonetic elements
comprising them?" (Mackay, 1970, pp341-346)
This sort of progressive encoding and recoding, of course, is classic material for a box-and-arrow explanatory diagram, and, sure enough, Mackay obliges .....
|
Figure 1 -
Mackay's (1970) Speech Production Model: Here is a relatively straightforward four-box model of the lower levels
of the speech motor hierarchy. Lexical selection has already taken place, and
the selected items "displayed" in the buffer system,
"abstractly represented in correct serial order". Here is what
happens next ..... "When
this buffer system contains a word the corresponding phonemic units at the
Individual Phoneme Level [topmost green box] become partially activated,
along with a set of programs for modifying these phonemes at the Contextual
Integration Level [middle green box]. These levels in turn feed into the
Motor Unit Level [lower green box], where reciprocal inhibition is assumed to
occur. These motor units code the contextual variants of phonemes, [.....]
The units at the Individual Phoneme Level are unordered, and are activated in
correct serial order through scanning of the buffer system." (Mackay,
1970, p348) If this diagram
fails to load automatically, it may be accessed separately at |
|
Redrawn from a
black-and-white original in Mackay (1970; Figure 7). This graphic Copyright ©
2003, Derek J. Smith. |
1.3 The
"Tip of the Tongue" Phenomenon
This is the name given to the relatively common everyday experience where we more or less know the word we want to say next, but are unable to bring it all the way to consciousness. The phenomenon has been known about for some time, but recent interest is normally dated to Brown and McNeill (1966), who carried out psycholinguistic research on 56 American undergraduates. They selected 49 low-frequency words (such as apse, nepotism, cloaca, ambergris, and sampan) and prepared brief dictionary definitions of each. Subjects were given a response sheet (similar to that used in Exercise 2 below), and were then presented with each definition (just like opening a dictionary at random, reading an entry, and then trying to guess the word to which it refers). Where subjects either knew or did not know the target word, no response was required, but on approximately 8.5% of trials, they experienced a tip-of-the-tongue (TOT) state - their lexicon had nearly delivered them up the target word, but not quite. On these occasions, they were required to guess at the missing word's first or last letters, the number of syllables it contained, and which syllable they thought carried the primary stress. However, before we discuss their results, here is an opportunity for you to experience the phenomenon for yourself .....
Exercise 2 - The Tip of the Tongue Phenomenon
Brown and McNeill's subjects experienced a total of 360 TOT states, of which 233 were "positive TOTs", that is to say, TOTs "for which the data obtained could be scored as accurate or inaccurate" (p280), and the remainder were "negative TOTs", that is to say, TOTs "for which the subject judged the word read out not to have been his target and, in addition, one in which the subject proved unable to recall his own functional target" (p281). The trials were also scored for whether TOTs were similar in sound (Saipan, perhaps, for sampan) or meaning (houseboat, perhaps, for sampan) to the target. There were 224 similar-sound (SS) TOTs, and 95 similar-meaning (SM) TOTs. Of the SS items, 48% had the same number of syllables as the target, compared to only 20% of the SM words. These data were then modelled as though the human word stores were organised like a dictionary, albeit a very complicated one .....
"In
real dictionaries, those that are books, entries are ordered alphabetically and
bound in place. Such an arrangement is too simple and too inflexible to serve
as a model for a mental dictionary. We will suppose that words are entered on keysort cards instead of pages and that the cards are
punched for various features of the words entered. With real cards, paper ones, it is possible to retrieve from the total deck any
subset punched for a common feature by putting a metal rod through the proper
hole. We will suppose that there is in the mind some speedier equivalent of
this retrieval technique. The model will be described in terms of a single
example. When the target word was sextant, subjects heard the
definition: 'A navigational instrument used in measuring angular distances,
especially the altitude of sun, moon, and starts at sea'. This definition
precipitated a TOT state in 9 subjects of the total 56. [.....] The problem
begins with a definition rather than a word and so the subject must enter his
dictionary backwards, or in a way that would be [.....] quite impossible for
the dictionary that is a book. It is not impossible with keysort
cards, providing we suppose that the cards are punched for some set of semantic
features. [..... However] in the TOT case the [retrieval] must include a card
with the definition of sextant entered on it but with the word itself
incompletely entered." (Brown and McNeill, 1966, pp292-293; italics
original)
Brown and McNeill then discuss at length exactly how this incomplete lexical entry might be coded. The most obvious suggestion was that it was coded by its first and last letters, so that saucepan, spaceman, and stamen would all be clustered together in some way - hence the Saipan-sampan confusion. But this was dismissed as a touch too simplistic. Instead, they preferred "something more like Sex_tanT" (p295), where not just the first and last letters, but also elements of the first and last syllables also played a part. Brown and McNeill named this type of recall by common feature "generic recall", and saw it as reflecting the coding systems used in verbal memory. This makes the TOT phenomenon itself, as well as the techniques of experimenting with it, relevant across a wide spectrum of communicative cognition, including speech perception, sentence production, and reading, as now demonstrated .....
Exercise 3 - Accessing the Lexicon using First and Last Letters Only
More recently, Jones and Langford (1987) and Maylor (1990) have looked at how different types of distractor word can interfere with the TOT phenomenon. Maylor, for example, presented TOT items to 15 subjects in their 'fifties, 17 in their 'sixties, and 17 in their 'eighties. A distractor word was presented immediately after each target definition, separated only by a short bleep. These distractors had been carefully chosen to fall into one of four conditions. In Condition P the distractor was phonologically related to the target word (eg. baulk for braise), in Condition S it was semantically related (eg. incubus for banshee), in Condition U it was not related in either way (eg. fossilise for hospice), and in Condition PS it was simultaneously phonologically and semantically related (eg. abnormality for anachronism). They distinguish subjective TOT, where the subject reported the TOT state but could not retrieve any concrete facts about it, and objective TOT, where a letter or letters could be identified and a syllable count or stress location given. Their results indicated that both states occur more frequently when the distractor word was phonologically related to the target word than when it was phonologically unrelated.
And more recently still, Harley and Bown (1998) varied the frequency and phonological distinctiveness of the target words and found "that TOTs are more likely to arise on low-frequency words that have few close phonological neighbours" (p151). They use their data to reflect upon the broader process of "lexicalisation", which they define as "the process of phonological retrieval in speech production given a semantic input" (p152), and they opt for a "two-stage" explanatory model of lexical access, that is to say, a model which strictly separates each word's semantic and phonological representations. TOTs can therefore be seen as arising "when the first stage of lexical access is completed successfully, but not the second" (pp152-153). However, the critical point as far as Harley and Bown are concerned is as follows .....
"Our
central result is that phonological neighbours contribute to, rather than
hinder, phonological retrieval in speech production. [.....] A TOT occurs when
the semantic specification successfully accesses the abstract lemma. This causes the 'feeling of knowing' the word. Nevertheless,
the lemma is then unable to pass sufficient activation onto and thereby access
the corresponding phonological word form. [.....] There are two possible reasons
for failure at this stage. Either the connections between the lemma and the
phonological forms might be weakened, or the phonological forms might
themselves be weakly represented for these items." (Harley and Bown, 1998, p162)
Finally, although this section is primarily concerned with speech errors in normals, the similarity between the TOT phenomenon and the clinical sign known as "anomia" is too glaring not to get a comment. Goodglass, Kaplan, Weintraub, and Ackerman (1976) studied the confrontational naming ability of a population of aphasics, and began by pointing out this very similarity .....
"The
designation of a patient as 'anomic' indicates that his access to lexical terms
is poor in relation to the fluency of his articulation and grammar" (Goodglass et al, p145).
Goodglass et al then looked at patients' "tacit knowledge" of the first letter of, and number of syllables in, the words which they were failing to retrieve. In fact, they dated this sort of research to Weisenburg and McBride (1935), who formally recorded how many syllables anomics thought were in the lost names (a test known as the Proust-Lichtheim Test of Inner Speech, in which the patients show by raising an appropriate number of fingers how many syllables they believe are in the word they are having trouble with). In their own research, Goodglass et al tested 42 male aphasics, classified by the Boston Diagnostic Aphasia Test as 13 Broca's type, 8 Wernicke's type, 12 conduction type, and 9 anomic type. Each was shown 48 line-drawing stimulus cards of objects whose name was of intermediate word frequency in English, and containing one, two, three, or four-or-five syllables [for example, clamp, walrus, violin, and refrigerator). The authors conclude .....
"The
results indicated a clear cut superiority on the part
of conduction aphasics, as compared to Wernicke's and anomic subjects.
Conduction aphasics identified both first letter and syllabic length of one
third of the words which they could not name. Anomic aphasics succeeded in fewer than one of ten instances and Wernicke's aphasics were
not much more successful. Broca's aphasics were
correct in one try out of five, and could not be differentiated statistically
from either the conduction aphasics on the one hand or the Wernicke's aphasics
on the other." (Goodglass et al, 1976, p151)
As to why this should be, the authors looked at the sequential nature of the word production process .....
".....
it appears that word finding is usually an
'all-or-none' process for Wernicke and anomic patients, in the sense that they
either recover a name well enough to produce it or they can give little
evidence of partial knowledge. Words which are failed then seem to be totally
unavailable, as far as recall processes are concerned. However the near perfect
multiple choice selections by all subjects indicate that this is a one-way
disorder involving recall, but not recognition, [//] In the case of the
conduction aphasics the evidence of tacit partial knowledge of many words may
indicate a breakdown at a later stage in the naming process. An inner auditory
representation may be present but is prevented from setting into motion the
final neural events which activate the articulatory system. Either the auditory
model is incomplete or, as the disconnection hypothesis suggests, its route to
the motor speech area is not consistently available. [//] The failure of Broca's aphasics to match the performance of the conduction
aphasics is surprising, since it contradicts the traditional notion
that their word finding difficulty is purely at the motor speech
level." (Goodglass et al, 1976, p152)
Further differences between the conduction and transcortical motor types of aphasia are discussed in McCarthy and Warrington (1984).
1.4
Malapropisms
Malapropisms are another phenomenon where the empirical data challenge one's preferred model of lexical organisation, thus .....
"From
a collection of over 2000 errors in speech compiled by the first author, we
initially selected all errors that involved word substitution (397). From this
initial list we eliminated all errors that could have arisen from [other
sources]. The remaining corpus comprised 183 errors. These errors, the
malapropisms, have some interesting properties. First, the target and the error
are of the same grammatical category in 99% of the cases. Second, the target
and the error frequently have the same number of syllables (87% agreement in
our list). Third, they almost always have the same stress pattern (98%
agreement)." (Fay and Cutler, 1977, pp507-508).
Fay and Cutler continue .....
"At a certain point in the production of a sentence a grammatical structure must be framed to carry the meaning that the speaker intends to convey. This structure can be thought of as incorporating both the syntactic properties of the impending utterance (in the form, say, of a phrase structure), and the meanings of the words to be used. What is not in the structure initially is any specification of the phonological characteristics of the chosen words. For these the speech production device must look into its mental dictionary to find a particular entry whose meaning and syntactic category match the specifics embodied in the grammatical structure. [.....] What is this mental dictionary, or lexicon, like? We can conceive of it as similar to a printed dictionary, that is, as consisting of pairings of meanings with sound representations. A printed dictionary has listed at each entry a pronunciation of the word and its definition in terms of other words. In a similar fashion, the mental lexicon must represent at least some aspects of the meaning of the word, although surely not in the same way as does a printed dictionary; likewise, it must include information about the pronunciation of the word although, again, probably not in the same form as an ordinary dictionary." (Fay and Cutler, 1977, pp508-509; bold emphasis added; note that these authors are using the linguistic definition of lexicon, not the psycholinguistic - see glossary)
2 - Hesitations
as Indicators of Thinking Time
"'Time
is the measure of all things', not least mental activities; and time when
people appear to be doing nothing is the kind of time psychologists most like
to measure." (Butterworth, 1980, p155)
The idea that hesitation phenomena might indicate psychological processing time goes back to Donders' work in the 1860s, but modern interest is best placed with the work of Frieda Goldman-Eisler (various from 1951). In one of her early studies (Goldman-Eisler, 1958), she demonstrated that hesitation pauses preceded phrases rich in new information. She was then followed by Donald S. Boomer, who studied the relationship between both filled and silent pauses and their position within the grammatical clause (eg. Boomer, 1965). Boomer tape recorded spontaneous speech from 16 male American students, and analysed the transcripts for silences longer than 200 milliseconds, filled pauses, and the suprasegmental "phonemic clause" boundaries .....
Key Concept - Phonemic Clause: "A phonemic clause is an intonational unit consisting of a single intonation
contour, one primary stress and a terminal juncture, and is also called a 'tone
group'" (Butterworth, 1980, pp156-157). Alternatively, it is "a
grammatical structure produced within a single intonation contour, and bounded
by junctures [silences, or significant changes in phonetic pitch, stress, or
duration]." (Crystal, 2003, p348)
Boomer then numbered the successive word boundaries in clauses, on the assumption that they presented "an ordered series of opportunities for hesitation" (p162). For example .....
1and 2the 3weather 4was 5hot
Here is his argument .....
"In
general, there will be as many possible locations as words in the clause, each
location being labelled with the ordinal number of the word it precedes.
Occasional arbitrary exceptions were made in this study for multiple-element
proper nouns such as Bill Smith and San Francisco, for
combinatory groups like thank you and what-you-may-call-it, and
for certain 'tags' such as you know and you see. These were
counted as single words, as were syntactically superfluous repetitions of
words, as in I took the ... the train. Filled pauses themselves and
word-fragments were also excluded from the count. [//] The corpus contained a
total of 1593 phonemic clauses of which 713 contained one or more hesitations.
Hesitations totalled 1127, 749 unfilled pauses and 378 filled pauses. [.....] Results. The hypothesis that hesitations tend to occur at
the beginning of phonemic clauses was strongly supported [although] the
greatest frequency of hesitations is not at the outset but at position 2, after
the first word of the clause [see the column of data highlighted in red in the
table below - Ed.]. This is true for all nine of the array distributions
representing clause lengths from two to ten words." (Boomer, 1965,
pp162-163; italics original; bold emphasis added)
Rochester (1973) provides a handy review of the early literature on hesitations, if interested.
2.1 Lindsley's Work
Lindsley (1975) designed a study to determine how many sentence units are planned in advance of speech initiation. Noting that the subject and main verb introduces the part of the sentence known as the predicate, he identified three possible planning strategies, as follows .....
Pre-Predicate Model: This
model "characterises a speaker who initiates his utterance as soon as he
has completed selection of the subject" (Lindsley,
1975, p3).
Post-Predicate Model: This
model "characterises a speaker who delays initiating his utterance until
after he has completed selecting the verb as well as the subject" (Lindsley, 1975, p3).
Semi-Predicate Model: This is
a compromise model which "characterises a speaker who delays initiating
his utterance until after he has completed some selection of the verb as well
as selection of the subject" (Lindsley, 1975,
pp3-4)
Now the point about the three explanatory models is that they make different predictions on initiation latency. The pre-predicate model predicts that the to-be-selected verb contributes nothing to any speech initiation latency, and, by implication, that "the speaker responds as though he were treating the subject and verb as independent responses" (p3). The post-predicate model predicts that verb selection does contribute to the initiation latency, and, by implication, that "the speaker responds as though he were treating the subject and verb as interdependent aspects of a larger response unit: the sentence as a whole" (p3). And the semi-predicate model falls between these two extremes, accepting some contribution to latency from verb selection.
To test which model might be operating, Lindsley devised a picture-description task to generate response latency data. He presented subjects with pictures containing an actor (a man, woman, girl, or boy) engaged in a specific action (touching, kicking, greeting, etc.), and compared response latencies when producing utterances of different length and grammatical form .....
S-Only Sentences: Here the
subject had to name the actor depicted on the card. Example: "The
girl".
V-Only Sentences: Here the
subject had to name the action depicted on the card. Example:
"Greeting".
S-V Sentences: Here the
subject had to name both the actor and the action in sentence form. Example:
"The girl is greeting".
S-V-O Sentences: Here the
subject had to name actor, action, and object in sentence form. Example:
"The girl is greeting the boy".
The amount of lexical decision making was also varied by holding either S or V constant across a number of cards, so that (a) it would always be the girl, say, who was doing something (S constant), or (b) the action would always be greeting, say, regardless of which actor was depicted (V constant). Where a different S or V were possible, Lindsley codes them as dS, dS + dV, and dV sentences; where a constant S or V, Lindsley codes them as cS, cV, etc. Data were then obtained for all permutations of c and d and sentence type, including mixed sentences such as cS + dV. These data indicated (a) that it takes longer to initiate an S-V utterance than an S-only utterance, thus arguing against the pre-predicate model, and (b) that S+V utterances were shorter than S-only naming when the actor was already known, thus arguing against the post-predicate model. Lindsley therefore concluded .....
".....
it seems most likely that the speakers of S-V
sentences, represented by dS + dV
and cS + dV do employ consistently
a specific speech strategy characterised by the semi-predicate model. This
speech strategy entails an initial portion of verb selection being deliberately
performed before the initiation of the utterance. Whenever this initial portion
of verb selection occurs in series with subject selection or takes longer than
any parallel stages of subject selection, it delays the initiation of the
utterance until after it has been completed. [.....] The results of this
research, singling out the Semi-predicate model, are consistent with those of
the hesitation studies [citations] in demonstrating that speech is initiated
before all information about an utterance has been processed or linguistically
coded." (Lindsley, 1975, pp10-19)
Or to put it simply, we typically start talking to an idea as soon as we have decided on the subject and have some idea of the action we wish to describe.
2.2
Butterworth's Work
Butterworth (1975) studied not the individual pauses - what he termed "the microstructure of hesitation" - but rather the overall proportion of pausings to speech - "the macrostructure of hesitation" (Butterworth, 1975, p75). He adopted Henderson, Goldman-Eisler, and Skarbek's (1966) concept of the "temporal cycles" of speech, that is to say, alternating periods of hesitancy and fluency, and collected speech samples from eight male subjects. He then analysed transcripts of these samples for the demarcation points of both the cycles and the Ideas. Here are his conclusions .....
"Clause
boundaries appear to be a necessary but not sufficient condition for the onset
of both cycles and new Ideas, in that the vast majority of cycles and the Idea
divisions given by any subject coincided with clause boundaries but a very
substantial number of clause boundaries were not coincident with either cycles
or Ideas. There was somewhat better match between sentences, Ideas, and cycles.
Taking Ideas and sentences first, of 35 criterial Ideas
boundaries - ie. where
more than half the subjects agreed on the location of an Idea division - all
but four coincided with sentence boundaries [.....]. Thus, of clause types, the
relevant kind for Ideas seems to be sentences; but Ideas may consist of more
than one sentence. [//] With regard to cycles, about half coincided with
sentence starts and three-fourths will all kinds of clause boundaries. this
left cycles consisting of more than one sentence in some cases and parts of
sentences in about half the cases [.....//] The results presented here are
consistent with the hypothesis that the cycles represent integral planning
units for the speaker, and shed light on what these planning units consist of
linguistically. First, the speaker tends to plan ahead in terms of
well-understood linguistic units - namely clauses and sentences. Second, he appears
to have the ability to chunk together several clauses or sentences as one
superordinate planned structure integrated by some kind of semantic unity.
[.....] If this is correct, then serious qualifications are required of
Boomer's thesis that the main unit of planning is the phonemic clause (Boomer,
1965; Boomer and Laver, 1968). If speakers do encode speech into phonemic
clause units, then this will occur well down the hierarchy of encoding
processes and will be a process of a quite different kind from the planning of
cyclic segments." (Butterworth, 1975, pp83-84)
In a later paper, Butterworth (1980) revisited the importance of hesitation data. He began by pointing out that sentence boundary pauses probably help listeners as much as speakers, because they give them time to consolidate their understanding of the message just received. He then drew again on the cycles described by Henderson, Goldman-Eisler, and Skarbek (1966) .....
"Typically,
cycles last about 18 s, but some as long as 30 s, which means that they will
contain, on average, five to eight clauses, ie. generally two or more sentences [citations]. Since, as we
have seen, semantic factors were responsible for pause time variations, we
should look for semantic rather than syntactic units. [//] I therefore asked
independent judges to divide transcripts of speech like 'Ideas' [.....]. Taking
those points in the texts where more than half the judges agreed that one Idea
ended and the next began, and comparing these with cycle boundaries, a significant
correspondence between Idea and cycle boundaries was found. Although the
correspondence was reliable it was not complete. Some cycles did not begin at
an Idea boundary, and some Ideas did not coincide with cycles. Why these
discrepancies should occur is not clear. [.....] One thing is established,
however: both Idea and cycle boundaries almost invariably coincide with clause
boundaries." (Butterworth, 1980, p165; bold emphasis added)
Butterworth is another to buy into the buffer
system concept, and, indeed, points out that there may well be more than one of
the things to have to worry about .....
"Several
authors, most notably Morton (1970), have argued for a 'Response Buffer' which
can hold a string of words for output following lexical selection. This buffer
is held to operate in both speech production and short-term memory tasks.
[However,] Shallice and Butterworth (1977) reported one case of severe
impairment of auditory-verbal STM, without a concomitant increase in the
hesitancy of speech. The most plausible interpretation of these results is
that, contra Morton, the buffer used in STM tasks is not used in
speech." (Butterworth, 1980, pp165-166; italics original; bold
emphasis added)
2.3
Developmental Data
Finally, MacWhinney and Osser (1977) give some developmental data. They studied 20 British five year olds, and analysed their hesitation behaviour by sex and social class. They concluded as follows .....
"The
first major result of this study has been the identification of three major
planning functions: preplanning, coplanning, and
avoidance of superfluous vocalisation. The styles in verbal planning reflect
basic differences in cognitive processing. Underlying all three planning
function, however, is one central commonality - verbal planning takes time.
While the speaker is trying to figure out what to say and how to say it, the
conversation moves on. Given this inevitable forward movement in time and his
own problems in formulating his utterance, the speaker may do one of two
things. He may attempt to fully formulate what he is going to say before he
says it. Alternatively, he may start talking and hope to be able to figure out
his utterance in medias res. Whether he pauses initially or attempts to patch
together an ongoing sentence, he has a further option. He may either use
superfluous verbalisation to cover his pauses and errors or he may simply
remain silent. The principal components analysis in this experiment indicates
that the 13 hesitation phenomena examined in this study can be grouped into these
three functional categories: coplanning, preplanning,
and avoidance of superfluous verbalisation. [.....] The second major result of
this study has been the finding that, for 5-year-olds, differences in verbal
planning functions are more related to sex than to social class. Boys were
found to do more coplanning, while girls made greater
use of preplanning. Moreover, boys showed more use of superfluous
verbalisations than girls." (MacWhinney and Osser, 1977, p984)
3 - Lexical
Structure Models
In this section, we look in more detail at the ins and outs of lexical retrieval .....
3.1 The
Spreading-Activation Theory of Lexical Retrieval
Having considered the many threads of evidence then available to him, Dell (1986) proposed a "Spreading-Activation Theory" of lexical retrieval. Here is the main thread of his argument .....
"The
principal assumption of the theory is that at each level a representation of
the sentence-to-be-spoken is constructed. Thus, a planned utterance will exist
at various times as a semantic, syntactic, morphological, and a phonological
representation. The theory describes the construction of the latter three
representations. [.....] The construction of a representation at each level
goes on simultaneously with that of the other levels [ie.
parallel processing - Ed.], with the rate of processing depending on factors
intrinsic to the level and on the rate of processing of the level immediately
above it. [.....] The basic idea of the theory is that the tagged nodes
constituting a higher representation activate nodes that may be used for the
immediately lower representation through a spreading-activation mechanism. The
lower representation is constructed as the generative rules associated with
that level build a frame, or ordered set of categories, and the insertion rules
fill in the slots of the frame [.....]. When an item is selected for a slot, it
becomes part of the developing lower representation and so it receives its tag.
Thus, a principal mechanism for the translation of information from one
representation to another is spreading activation through the lexicon.
[.....] When a node has an activation level greater than zero, it sends some
proportion of its activation level to all nodes connected to it (spreading). This
proportion is not necessarily the same for each connection. When the activation
[reaches] its destination node, it adds to that node's current activation level
(summation). [.....] Activation is assumed to decay exponentially [over time]
towards zero. These operations, spreading, summation, and decay, apply to all
of the nodes in the lexical network at all times, regardless of whether the
node is part of a representation (tagged or not). [.....] One of the important
assumptions regarding spreading activation in the theory is that all
connections are two way. If Node A connects to B, then B connects to A. Given
the nature of the connections and the hierarchical structure of the lexical
network, each connection can be classified as either excitatory top-down, or excitatory bottom-up. For each top-down connection,
such as that from a particular morpheme to a particular phoneme, there is a
bottom-up connection in the reverse direction. These bottom-up connections
deliver positive feedback from later to earlier levels and play a critical role
in the theory. Their presence makes processing in the network highly
interactive [and] generates some nonobvious predictions. [.....] Constructing
Representations: In this section I outline how a lower representation is constructed
given a higher representation. The first important concept is that of the current
node. It is that item of the higher level representation that is in the
process of being transferred into corresponding items at the immediately lower
level. [.....] When the construction of a lower representation begins, the
current node is that node of the higher representation that is tagged as first.
The initial step in the translation is the activation of the current node."
(Dell, 1986, pp287-288; italics original; bold emphasis added)
The big question, of course, is which processes go wrong to produce a given error, and Dell's simple answer was that "no one process is at fault" (p289). Speech errors are simply natural consequences of the way the mind is organised. Thus .....
"For
example, in the planning of an utterance many concepts would legitimately
become activated that would not actually appear in the utterance. This
background activation might include activation from concepts that were either presuppositions
or inferences that were necessary in the semantic and pragmatic planning of the
utterance. For example, if one were to say Could you close the door?, one would
certainly have processed the presupposition that the door was open. As a result
the concept for open might be active, and because of the spreading
activation, the word, morpheme, and phoneme nodes associated with [it] would
become activated, perhaps resulting in the slip Could
you open, I mean close ....." (Dell, 1986, p291; italics original)
The error corpus data on the location of errors are also important .....
"In
general, items are more likely to move short distances. Misordered
sounds and morphemes tend to move to adjacent content words that are in the
same phrase (Boomer and Laver, 1968; Garrett, 1975; MacKay, 1970). Misordered words move greater distances, possibly because
the planning chunks at the syntactic level are larger, or because words can
only move to appropriate syntactic slots (Garrett, 1975)." (Dell, 1986,
p293)
4 - Modular
Speech Production Models
Dell's theory deals primarily with word retrieval at a micro level. It accepts the basic two stage theory and identifies four levels of representation within those stages, but although it has a lot to say about what might be going on at neural levels, it does not fully address the modularity of the processing. Other workers have taken a more macroscopic view, and have not only tried to map the modules and processes involved in speech production, but have started to push upwards into the realms of pragmatics.
ASIDE: Praxis and pragmatics
actually share the same linguistic root, namely the Greek word prassein = "to do", via its derivations praxis
("doing") and pragma ("deed"). Defects of praxis are
known as dyspraxias. We have already dealt at
length with the motor hierarchy under a number of separate headings. For
example, it is the output leg on the standard A-shaped control hierarchy model.
For specific examples see Craik (1945), Frank (1963), and Norman (1990), for the history of the motor hierarchy in general
see our e-paper
on "The Motor Hierarchy",
and for an introduction to theories of biological motor programming, see our e-paper
on "Motor Programming". And
the motor hierarchy for speech is one of the output legs on the standard
X-shaped psycholinguistic transcoding model. See, for example, Ellis (1982), Ellis
and Young (1988), and Kay, Lesser, and
Coltheart (1992). For the history of
this model layout, see our e-paper
on "Transcoding Models".
In this section, we shall look at some of the most influential of these modular models.
4.1 Lordat's Very Early Speech Production Model
This is the subject of a dedicated separate paper. See Lordat (1843).
4.2 Other Early
Speech Production Models
Lordat's was the first of many 19th century speech production models, of which the following may be worth a quick browse, if interested in the historical aspects of the subject .....
Lichtheim (1885) (still the standard model for 21st Century medical training)
4.3 Shannon's
Idealised Communication Model
The late 1940s saw a wave of interest in the engineering aspects of communication. This led to telecommunications experts borrowing freely from the aphasiology literature, and, in turn, to psycholinguistics borrowing back much of the resulting vocabulary during the ensuing decade [specifically, words such as encoding, information, working memory, signal-to-noise ratio, and feedback]. The engineer who did most to systematise the way we look at communication and its failures was Claude Shannon, then with the Bell Telephone Company [fuller story in our e-paper on "Shannonian Communication Theory", if interested].
4.4 Fromkin's "Utterance Generator" Model
The 1950s saw increasing interest in psycholinguistic experimentation, with major works by George Miller (Miller, 1951), Colin Cherry (Cherry, 1957), and Roger Brown (Brown, 1958). This experimentation was complemented by an expanding literature on the psycholinguistic impact of brain damage led by the likes of Harold Goodglass (1920-2002) and Norman Geschwind (1926-1984). This groundwork then generated a number of explanatory models across psychology as a whole. Donald Broadbent became one of the lead-theorists for selective attention, John Morton did the same for modular language processing, Atkinson and Shiffrin did the same for short-term memory, and Alan Baddeley added working memory. The pivotal work in the field of speech production was Fromkin's (1971, 1973) "Utterance Generator" model, which largely resurrected Lordat's 19th century scheme of things with the following six-stage explanatory analysis .....
Stage 1 Processing - Semantic System: This is where the meaning to be conveyed is first generated.
Stage 2 Processing - Syntactic System: This is where an appropriate syntactic
"slot" structure is decided upon.
Stage 3 Processing - Lexical System: This is where content words are extracted from the lexicon to help
give shape to the developing sentence.
Stage 4 Processing - Prosodic System: This is where an appropriate intonation pattern is decided upon.
Stage 5
Processing - Phonological Assembly: This
is where function words [glossary]
are inserted at key points in the emerging sentence structure, and then
abstract sounds attached to the words and morphemes as they fall into position
within each clause.
Stage 6 Processing - Phonetic System: This is where concrete sounds are attached to the abstract sounds, and
muscle activation commences.
|
Exercise 4 - So
is it Six Stages or Three? Most of the 19th century models settled for three or four stages of speech production, and Requin, Riehle, and Seal (1988) have argued that three hierarchical processing levels is nature's norm for biological motor behaviour. Yet most of the models mentioned in this section end up with five or six. Suggest how this apparent disagreement might be explained. |
4.5 Garrett's
Speech Production Model
This is the subject of a dedicated separate paper. See Garrett (1990). [At two points in his model, Garrett shows two processes dealing with different aspects of the processing simultaneously - thus going some way towards fitting six processes into only three processing modules.]
4.6
Butterworth's Modern Speech Production Model
Drawing on both Fromkin and Garrett, Butterworth (1985) offers a flow diagram similar to Garrett's, in which the following "processing systems, or modules" are identified .....
Semantic System: This is Fromkin's "Stage 1 Processing" as defined above.
Butterworth regards it as passing information to "the next three systems
in parallel" (p68).
Syntactic System: This is Fromkin's "Stage 2 Processing" as defined above.
Butterworth regards it as receiving the first of the three streams of
information coming out of the semantic system, and as using this information to
set up appropriate sentence and clause constructions.
Lexical System: This is Fromkin's "Stage 3 Processing" as defined above.
Butterworth regards it as receiving the second stream of information coming out
of the semantic system, and as using this information to select suitable words
"from an inventory - lexicon - of word forms" (p69).
Prosodic System: This is Fromkin's "Stage 4 Processing" as defined above.
Butterworth regards it as receiving the third stream of information coming out
of the semantic system, and as using this information to choose "an
appropriate intonation contour" (p69).
Phonological Assembly System: This
is Fromkin's "Stage 5 Processing" as
defined above. Butterworth regards it as setting up a "phonemic string
with syntactic bracketing".
Phonetic System: This is Fromkin's "Stage 6 Processing" as defined above.
Butterworth regards it as taking the output from the Phonological Assembly
System, and as then generating suitable motor commands. This is the point at
which the abstract phonemes begin to turn into concrete phones [glossary].
It is also the point at which coarticulation takes
place.
|
Figure 2 - Butterworth's
(1985) Speech Production Model: This
diagram lays out the modules described above in the now-familiar general
layout. We shall therefore comment only on the model's uniquenesses .....
If this diagram fails to load
automatically, it may be accessed separately at |
4.7 Levelt School Models
Levelt (1989) published a major monograph on speech production under the title "Speaking: From Intention to Articulation". As head of the Max Planck Institute for Psycholinguistics, one of his major points was to consider the difference between "lexical encoding", the retrieval (and creation if necessary) of words to express ideas, and "syntactic encoding", the retrieval and sequencing of words to express ideas .....
"But
languages differ enormously in the degree to which they exploit [lexical
encoding]. While a Turkish speaker's grammatical encoding consists for the most
part of such lexical encoding, an English speaker is extremely 'conservative'
in the sense that he normally uses words he has heard often in the past. For
the English speaker, lexical encoding plays a minor role in grammatical
encoding; the action is in syntactic encoding. A theory of the speaker should,
of course, encompass both kinds of grammatical encoding. As a matter of fact,
however, almost nothing is known about the psychology of lexical
encoding." (Levelt, 1989, p186)
In an attempt to cast some light on the processes of lexical encoding, Levelt did much to popularise the use of the term "lemma" [see earlier discussion, Section 1.3]. Thus .....
".....
from the point of view of language production a
lexical entry can be split up into two parts: its lemma and its form
information []. This theoretical distinction can be extended to the mental
lexicon as a whole. Lemmas can be said to be 'in the lemma lexicon', and morpho-phonological forms to be 'in the form lexicon'. Each
lemma 'points' to its corresponding form. [.....] The semantic
information in a lemma specifies what conceptual conditions have to be
fulfilled in the message for the lemma to be activated; it is the lemma's meaning.
These conditions can be stated in the same propositional format as messages.
[.....] A lemma's syntactic information specifies the item's syntactic
category, its assignment of grammatical functions, and a set of diacritic
feature variables or parameters." (Levelt, 1989,
pp187-190)
Further down the system, Levelt sees the process of phonological encoding as working this way .....
"Phonological
encoding is a process by which the phonological specifications of lexical items
are retrieved and mapped onto a fluently pronounceable string of syllables.
Unpacking a word's phonological specifications and using them to retrieve the
appropriate syllable programs involves various levels of processing. Studies of
the tip-of-the-tongue phenomenon in which this process of phonological
unpacking is blocked or slowed, support this view." (Levelt,
1989, pp361-362)
Two years later, Donald (1991) drew on Levelt's work in his own "evolutionary" theory of the speech motor hierarchy .....
|
Figure 3
-Donald's (1991) Speech Production Model: This model was developed from earlier models by Butterworth (1980,
1985) and Levelt (1989). It places a Linguistic
Controller L at the top of a "vertically integrated" speech system.
L then creates "narrative models" out of ideas released to it (a)
from episodic memory as the result of current stimulation, and (b) from a
mental structure he calls the Mimetic Controller, a hypothetical
mechanism believed to be responsible for the production of "conscious,
self-initiated, representational acts that are intentional but not
linguistic" (Donald, 1991, p168) [this being nothing less than the
evolutionary advance which brought about the emergence of the modern human].
The lower processes are jointly responsible for the "lexical assembly"
of the final utterance. This brings in subprocesses
for selecting, sequencing, and determining the correct form of the words to
be produced. The Phonetic Plan "maps the assembled utterance onto neuromotor paths and, ultimately, the vocal musculature".
All this makes for the generally familiar layout, so again we only need to
point out the model's uniquenesses .....
If this diagram fails to load
automatically, it may be accessed separately at |
|
Redrawn from a black-and-white
original in Donald (1991, p260; Figure 7.2). This graphic Copyright © 2003,
Derek J. Smith. |
Finally, Levelt, Roelofs, and Meyer (1999) are typical of the latest offering from Levelt's research unit .....
|
Figure 4 - Levelt, Roelofs, and Meyer's
(1999) Speech Production Model:
This diagram, too, adopts the now familiar general layout, so again we shall
note only its points of uniqueness .....
If this diagram fails to load
automatically, it may be accessed separately at |
|
Redrawn from a
black-and-white original in Levelt, Roelofs, and Meyer (1999, p3; Figure 1). This graphic
Copyright © 2003, Derek J. Smith. |
5 - Feedback in
Speech Production Models
The topic of feedback was introduced in our e-paper on "The Basics of Cybernetics", and is especially important to speech production theory. Gracco and Abbs (1987) are among many to point out that continuous speech involves continuous feedback, that is to say, that the continuous execution of a motor program requires an equally continuous stream of sensory information from muscle and cutaneous senses throughout the respiratory, laryngeal, and orofacial regions. Similarly, but at a higher level of analysis, Levelt (1989) devotes an entire chapter to the topic of self-monitoring and self-repair. Among the types of feedback Levelt deals with are .....
* Am I saying what I meant to say?
* Is this the way I meant to say it?
* Is what I am saying socially
appropriate?
* Am I selecting the right words?
* Am I using the right syntax and
morphology?
* Am I making any phonological
errors?
* Is my articulation at the right
speed and pitch?
Successful speech production, in other words, is a constant battle against error, and those errors can pop up anywhere. The phrases we then use to interrupt and correct ourselves (phrases such as "sorry", "I mean", "let me put that another way", etc.) are known generically as "editing expressions" (Hockett, 1967). Levelt (1989) summarised the issue thus .....
"The
major feature of editor theories [of monitoring] is that production results are
fed back through a device that is external to the production system.
Such a device is called an editor or a monitor. This device can
be distributed in the sense that it can check in-between results at different
levels of processing. The editor may, for instance, monitor the construction of
the preverbal message, the appropriateness of lexical access, the
well-formedness of syntax, or the flawlessness of phonological-form access. There
is, so to speak, a watchful little homonculus
connected to each processor." (Levelt, 1989,
pp467-468; italics original; bold emphasis added)
In this section, we look at how feedback and editing have been studied objectively .....
5.1 Early
Studies
Lee (1951) pioneered a technique of replaying a person's speech to that person's own ears, subject to a variable time delay. Here is how he profiles his method .....
"In
order to produce delayed speech feedback, it is necessary to return the
speaker's speech to his own ears approximately one quarter second after he has spoken.
This is best accomplished by means of a magnetic tape [machine]. The subject
reads a moderately difficult text into the recording microphone with the
playback gain control to the telephone headset turned off, and a normal reading
pattern is established. The playback gain to the earphones is then advanced
until the subject's speech is disturbed." (Lee, 1951, p53)
Using this experimental set-up, Lee found that there were two types of common effect. Subjects either (a) slowed down and raised their voices, or else (b) began to speak haltingly, repeating syllables in a form of "artificial stutter". The same phenomenon emerged with skilled tympanists reading a drum-beat, and for the key presses of skilled Morse Code operators. Lee gives the following specific examples .....
aluminum..... degrades to aluminum-num.....
ten-nine-eight-seven....
degrades to ten-nine-nine-eight-seven.....
Lee interpreted these findings as evidence of a multiple loop control hierarchy, with four levels of feedback, as follows .....
The "Thought Loop":
The top control level releases individual thoughts for action, and then
monitors that action for successful progress and completion. The highest level
feedback loop then monitors the output for what would nowadays be termed its pragmatic
appropriacy [strictly speaking, its "perlocutionary
effect"].
The "Word Loop":
The second highest loop monitors speech production for word selection accuracy.
The "Voice Loop":
The third highest loop monitors speech production at whole-syllable level for
morphological accuracy.
The Articulating Loop":
Finally, the lowest loop monitors speech
production checking that the right phonemes
have been used within each syllable.
It is confusion at the hand-over between the second and the third level which presumably causes the aluminum-num syllable repetition. There were no single-phoneme repetitions. Here is Lee's own conclusion .....
"The
satisfaction at each stage by a monitoring system is required; otherwise the
machine halts, repeats, or repeats corrected. Repetition of sentences and words
is volitional for emphasis, increased clarity, or correction of gross errors.
Repetition of syllables is probably involuntary, or reflex, and it is at this
stage that artificial stutter is manifested. Repetition of phonemes has
not been artificially induced by delayed speech feedback in [our] observation
....." (Lee, 1951, p54)
So compelling were these early studies, that Mysak (1966) explicitly put cybernetics and speech pathology in bed together in his book "Speech Pathology and Feedback Theory".
5.2 Editing and
Editing Expressions
Motley, Camden, and Baars (1982) argued the existence of a function of "prearticulatory editing", as follows .....
"Editing
has been described as a phase of speech production which occurs after the
phonological phase (ie. after
the impending message has evolved its phonological representation) but before
the articulatory phase, and which operates to test or check the linguistic
integrity of the incoming phoneme strings. The edit presumably approves for
subsequent articulation those phoneme strings which are linguistically
appropriate; but vetoes and attempts to replace those which are linguistically
anomalous, thus preventing their articulation." (Motley, Camden, and Baars, 1982, p578)
Motley et al then carried out a dozen or so studies in the late 1970s and early 1980s on cleverly induced Spoonerisms. They called their method SLIP - for "Spoonerisms of Laboratory-Induced Predisposition", explaining it as follows .....
"Subjects
are instructed to read silently a series of tachistoscopically-presented
word pairs, speaking aloud certain cued 'target' pairs. Unbeknownst to the
subject, these target word pairs are immediately preceded in the series by
'interference' pairs designed to phonologically resemble the spoonerised version of the intended target. For example,
the subject might read silently the interference items barred dorm and bought
dog immediately before seeing and attempting to articulate the target darn
bore. About 30% of subjects' attempted target utterances result in a
spoonerism - barn door in this example. Our most typical design has been
to compare the frequency of anomalous versus legitimate error utterances;
anomaly being defined according to various linguistic and quasi-linguistic
criteria." (Motley, Camden, and Baars, 1982,
p579; italics original)
They then compared what they call the "slip-rate differential" between "legitimate" Spoonerisms and "anomalous" ones .....
"Our
most typical result is that legitimate errors far outnumber anomalous ones. For
example, a lexically legitimate SLIP spoonerisms like darn boor > barn
door will occur much more frequently than a similar but lexically anomalous
one like dart board > bart
doard. [//] This slip-rate differential [has]
been the primary form of evidence for prearticulatory
editing. That is to say, the above example [.....] can be taken as evidence
that when the SLIP subject constructs a lexically legitimate phoneme string,
the string is allowed to be output; whereas when the subject constructs
lexically anomalous potential output, it is vetoed (by the edit), and its
articulation is disallowed." (Motley, Camden, and Baars,
1982, p579; italics original)
As to the underlying neural mechanisms, Crosson (1985) offers a view of speech production involving Broca's area, Wernicke's area, and various substructures of the thalamus and basal ganglia, all interlinked by circulating and re-circulating white matter tracts, and delivering both semantic and phonological monitoring. For details, see the separate paper, Crosson (1985).
|
Exercise 5 -
Improving the Diagrams Levelt's model has lost Butterworth's two-part higher functions system, so it fails to separate semantics and pragmatics. It has also lost Garrett's sentence type and clause structure frames, does not deal at all well with parallel processing [we criticise merely the diagram here, which does not reflect the full richness of the Levelt School's broader theory], and has only one "up arrow" when there are potentially many. Use your diagramming skills to produce a bigger, better, model [in other words, add in Levelt's "watchful little homonculus", if you can, and wherever you can]. |
6 -
Pathological States Attributable to Defective Biological Control Systems
Now the reason box-and-arrow models are so important to clinicians is that there a number of very well known communication pathologies - not least, stuttering, dyspraxia, and dyslexia - which are actually cybernetic problems at heart. We have already covered stammering in Section 5.1, so here are some of the others .....
6.1 Dyslexia
Resulting from Poor Head/Eye Muscle Control
Dyslexia is an inability to process visually presented text efficiently. Whilst this is at first sight a perceptual problem, the very complexity of the oculomotor control system makes it a motor problem as well. You cannot read if you cannot control the movement of your eyes. When reading this text, for example, your eyes will be fixating after every eight characters (about every one and a half words) (Rayner and Pollatsek, 1989), and many authorities (typically Pavlidis, 1981/1985) believe that developmental dyslexia can be explained by defects in sequencing these fixations for maximum information uptake. Developmental dyslexics do appear to have eye movement patterns which differ from those of normal readers (Rayner and Pollatsek, 1989). However, this factor per se has not been strongly confirmed. Indeed, Rayner and Pollatsek place greater store in Stein and Fowler's (1982, 1984) findings of "vergence control" problems in dyslexics. Vergence movements are those which keep both eyes pointing at the same centre of attention. In normal readers, the two eyes move "conjugately", that is to say, they track at the same speed and in the same direction. Stein and Fowler's data suggests that about one in six cases of developmental dyslexia can improve reading performance with treatment of this problem in isolation.
As to the cybernetics of eye control, the oculomotor control system serves a variety of biologically essential behaviours such as food search and predator avoidance (Galiana, 1990). It therefore needs to be every bit as functionally sophisticated as the skeletomuscular system it is helping to guide. This functionality is provided by having a complex of feedforward, predictive, and feedback control loops at work. To start with, there are mechanisms controlling the automatic focussing of the lens, binocular vergence, and the automatic stopping down of pupillary aperture. There are then additional mechanisms to control the automatic positioning of the eye relative to the head as the head moves relative to both the body and the external world. These latter mechanisms place heavy information processing demands on the vestibular system, the system which processes the information provided by the semicircular canals of the inner ear (the "labyrinth"), the body's balance detectors. Information from the semicircular canals travels to the brainstem down the vestibular branch of the vestibulocochlear nerve (CN VIII). Here it links in via the vestibular nuclei of the lower pons to the cerebellum and a host of other components of the extrapyramidal system. Good reviews of this subject area can be found in Peterson and Richmond (1988), Galiana (1990), and Berthoz, Graf, and Vidal (1992).
6.2
Parkinsonism
The motor disorders which characterise Parkinson's disease are conventionally attributed to disorders of muscle control circuitry. Wiener himself likened Parkinsonian tremor to the oscillations of under-"damped" control loops (Wiener, 1950), Flowers (1978) blames lack of prediction, Harrington and Haaland (1991) blame "central processing deficits", and Dinnerstein, Frigyesi, and Lowenthal (1962) blame slower than normal proprioceptive feedback for a variety of the standard Parkinsonian symptoms, such as rigidity, slowness, and lack of coordination.
6.3 Learning
Difficulties
Many categories of learning difficulty present with an inability (amongst other things) to communicate effectively at a pragmatic level. This can be alleviated to a greater or lesser extent by training at what Williamson (1992) describes as "backchannel" skills. These include a wide variety of both vocal and nonvocal responses, such as nods, shakes, grunts, facial expressions, etc., whose function is to feed back to a speaker the extent to which his/her utterances are being understood. [This, by definition, must be working to Lee's highest level feedback loop - the "thought" loop.]
6.4 Anomia
Anomia is an inability to find the name-word for something which is otherwise perfectly well understood. It is a very common clinical sign, and can arise from a variety of disease processes, both focal and diffuse, although it is particularly associated with injuries to the angular gyrus (Marshall, 1980). In its simplest form, anomia presents as difficulty with confrontational naming tasks, although the ability to describe a concept tangentially in the hope that this will compensate for the absence of its proper name is frequently preserved. Thus a patient might say "you cut your food with it" if s/he could not access the word "knife". This stratagem is known as circumlocution. It is even possible for the lost target word to be included in the circumlocution even though it had been unavailable in isolation, as with "I'd use it to comb my hair" as a substitution for the word "comb" (Benson, 1979). Marshall (1980, p62) passes on a nice example of word finding difficulties in a patient describing a picture .....
"'That's
the ..... you know, the ..... very
much like they got on the ..... on something very
much. I don't say that it's the proper one but it's like er
er .....
I can't say it but I can just ..... yes,
that could be it, could be a bit like that, yes. [etc.]
(Marshall, 1977)."
As far as the explanatory models are concerned, we are fortunate that they were originally drawn up with anomia in mind. Driven by the mass of clinical data accumulated since the 1860's, all modern models consistently separate ideation from word selection, that is to say, they separate the semantic system from the output lexicons [this being the crucial difference between the linguistic and psycholinguistic usage of the word lexicon]. Gnosis is what the semantic system does, and naming is what the speech output lexicon does. Morton himself relates anomic aphasia to problems moving outwards from the semantic system to the output lexicon, just as did the nineteenth century diagram makers before him. He then contrasts this with optic aphasia where there are problems moving inwards towards the semantic system from the visual input lexicons (Morton, 1985).
But anomic aphasia is not the only condition in which word finding difficulty is found. Benson (1979) distinguishes no less than nine subtypes, of which the following five are to some extent aphasic .....
(a) Word Production
Anomia: This is a confrontational
naming defect, but one which is resolvable upon phonemic cueing
(or "prompting"). If the patient is given the first letter of the
target word, the whole word suddenly becomes available. Patients can appear to
"know" the target name, but either cannot initiate its production at
all, or else produce a neologism instead. (This is therefore a condition
analogous to the "tip of the tongue" phenomenon discussed in Section
1.3 above.)
(b) Word Selection
Anomia: This is another
confrontational naming defect, but this time it is not usually resolvable by
cueing. Gnosis is intact (because patients can immediately point to the object
in question if told its name), and conversational speech is otherwise fluent
and effortless.
(c) Semantic Anomia: This is an inability to use an object's name as a
mental symbol. It is superficially similar to (b), but patients cannot point to
the object in question if told its name.
(d) Category-Specific
Anomia: This is an anomia for a
particular conceptual class of objects. It is quite rare, nevertheless it has
prompted authors such as Baron (1976) and Allport
(1985) to describe the semantic lexicon as having various regions (or
"zones", or "domains", etc.), each dealing with a particular
class of attributes. Thus an object's pictorial attributes, colour attributes,
positional attributes, "eye-head-body movement" attributes, and even
smell and taste attributes, are regarded as being stored in separate parts of
one large distributed engram system.
(e) Modality-Specific
Anomia: This is an anomia for objects
presented in one modality but not another (visual, for example, but not
auditory). However, it is probably best treated as an optic (or auditory)
aphasia, rather than as an anomia as such.
6.5 Agrammatism
This term derives from Kussmaul (1877) and refers to a Broca's-type aphasic condition characterised by sentence foreshortening and word morphology problems. The foreshortening is not haphazard, however, for it involves omitting many/all of a sentence's function words (articles, conjunctions, pronouns, prepositions, and auxiliary verbs) and inflectional word endings (-s, -ed, -ing). The end result is what is known as telegraphic speech, a word sequence built up mainly of nouns, but broken up by the occasional verb and qualifier (Goodglass and Menn, 1985). The conjunction "and" is often spared, although this may evidence a repair strategy more than a true cognitive ability. Here are some examples .....
"First
morning, drink coffee, and sweep and go field, afternoon such a pill, one and
go field ....." (Heilbronner,
1906, cited in McCarthy and Warrington, 1990.)
"Cinderella
... poor ... um 'dopted her ... scrubbed floor, um,
tidy ... poor, um ... 'dopted ... Si-sisters and
mother ... ball. Ball, prince, um, shoe ...[prompt to
continue] Scrubbed and uh washed and uh ... tidy, uh, sisters and mother,
prince, no, prince, yes. Cinderella hooked prince. (laughs).
Um, um shoe, um, twelve o'clock, ball /pInaSt/,
finished." (Schwartz, Linebarger,
and Saffran, 1985, p84; Patient "ME".)
Further examples in McCarthy and
Warrington (1985).
As far as the underlying anatomy is concerned
McCarthy and Warrington (1990, p185) conclude that "the [Broca's symptom complex] is often associated with
relatively widespread lesions affecting both anterior language areas (frontal
lobe), deeper structures (insula), as well as anterior temporal lobe
damage", and as far as the underlying processing is concerned Kolk, Van Grunsven, and Keyser
(1985) and Caplan (1985) have explicitly linked agrammatic
conditions to Garrett's model (which, it will be recalled, was originally
developed from speech error data from normal subjects). They conclude
that internal language is inherently telegraphic at the best of times, at least
at all stages prior to Garrett's functional stage.
A similar line of argument has been developed more recently by Grodzinsky (1990), who has approached agrammatism as a linguist. He describes surface speech as lacking both non-lexical terminals and governed prepositions. Indeed, in stark contrast to the anomias, the only thing agrammatic patients are left with is a naming ability! However, it is unlikely that a final answer will be possible until more is known about normal speech production, that is to say, until we have better speech production models to work with. (And, specifically, models which can link the hard facts of linguistic theory to the more advanced theories of semantic memory structure.)
|
Exercise 6 - Agrammatism Simulated 1 Rewrite the preceding paragraph to exclude all articles, conjunctions, pronouns, prepositions, and auxiliary verbs, and all noun- and verb-root endings. Read the residual text out loud. |
6.6 Jargon
Aphasia
The term "jargon aphasia" derives from Alajouanine, Sabouraud, and Ribaucourt (1952), and is "a rare and spectacular manifestation of an aphasic condition" (Butterworth, 1985, p61). By contrast with agrammatism, the phonology and prosody of the host language are retained, as are many of the rules of morphology (the nonsense is often appropriately matched for number, case, and gender). In addition, the patient is often blissfully unaware of the impairment. Three different syndromes have been identified (Butterworth, 1985) .....
(a) Semantic Jargon: This is where "the words employed, although real,
are semantically inappropriate, sometimes to the extent of seeming stripped of
their normal meaning" (Butterworth, 1985, p63). Here is a specimen: "Experimenter:
What does 'strike while the iron is hot' mean? Patient: Better to be
good and to Post Office and to Pillar Box and to distribution to mail and
survey and headmaster. Southern Railways very good and London
and Scotland" (Kinsbourne and Warrington, 1963;
Patient "EF", cited in Buckingham, 1985).
(b) Neologistic
Jargon: This is where speech includes
made-up words - words not found in the dictionary. Butterworth (1979) reports
that neologisms were used as nouns (61%), verbs (20%), or adjectives (15%) -
the categories known as content words, where each word must be chosen from a
large number of options. Neologisms were rare in function word context (4% in
total). Here is a specimen: "A man is asked the question, 'Who is running
the store now?' He replies, 'I don't know. Yes the bick,
uh, yes I would say that the mick daysys nosis or chpickters. Course, I
have also missed on the carfter teck.
Do you know what that is? I've, uh, token to ingish.
They have been toast sosilly. They'd
have been put to myafa and made palis
and, uh, myadakal senda
you. That is me alordisdus. That makes anacronous senda'"
(Buckingham and Kertesz, 1976, cited in Marshall,
1980, p62).
(c) Phonemic Jargon: This is where speech degenerates into a succession of
meaningless sounds, so that it becomes impossible to identify word boundaries.
Some phonotactic rules remain obeyed, as with the
clusters "tr", "nkr",
"str", and "mbr"
in the following specimen: "When asked to read the sentence It shall be
in the power of the College to examine or not examine any licentiate,
previously to his admission to a fellowship, as they shall think fit, he
produced the following: A the be what in the temother
of the trothotodoo to majorum
or that emidrate ein einkrastrai mestreit to ketra totombreidei to ra fromtreido as that kekritest." (Perecman
and Brown, 1981, p178; italics original.)
|
Exercise 7 - The
Three Jargon Types Simulated 1
Rewrite the next paragraph, replacing every second noun by a semantically
random word or short phrase (picked from a dictionary "with a
pin"). Read the resulting "semantic jargon" out loud. 2
Repeat (1), but this time replacing every fourth word with a made-up
(nonsense) word. Read the resulting "neologistic
jargon" out loud. 3 Just read the following "phonemic jargon" out loud "temother of the trothotodoo to majorum or that emidrate ". |
As far as the underlying anatomy is concerned, Kertesz (1981) reviewed ten cases of neologistic jargon in detail and found a significant pattern to the underlying lesions. He concluded that "the most consistently affected regions are the supramarginal gyrus, the posterior parietal operculum, the inferior parietal lobule, the first portion of the first temporal gyrus, the posterior temporal operculum (planum temporale), and the angular gyrus" (Kertesz, 1981, p100).
6.7 Dyspraxia
of Speech
Given our earlier definition of praxis, it follows that the essence of a dyspraxia has to be an impaired ability to initiate voluntary movements - an inability to move the tongue to lick the lips when commanded, for example.
ASIDE - PRAXIS VS REFLEX: It
is important to realise that the defect is solely one of initiating the
movement, and that the muscles and motor systems themselves are intact. If the
initiation is reflex or unwilled in any way - licking honey from the lips,
perhaps - the information comes across the standard A-shaped processing
hierarchy rather than down it, and the movement can be performed perfectly well!
Dyspraxic defects were first formally described by the German aphasiologist Liepmann (1900, 1905), and his explanation stuck closely to the speech production stages paradigm we saw so much of in Sections 3 and 4 above. Patients who cannot mentally conceive of having the required movement are deemed to have an ideational apraxia ('ideatorische apraxie'), patients who can have the idea, but not communicate that idea to the appropriate motor systems, are deemed to have an ideokinetic apraxia ('ideo-kinetische apraxie'), and patients whose motor systems cannot cope properly with the instructions sent to them are deemed to have a kinetic apraxia ('kinetische apraxie'). Subsequently, the German psychiatrist Kleist (1912) described the deficit of constructional apraxia, in which the ability to organise actions in space is affected. He regarded this as yet another disconnection syndrome, this time of the ability to transmit information between the processes of spatial analysis and those of voluntary action. A vivid description of dyspraxic speech is given by Darley, Aronson, and Brown .....
"As
they speak, they struggle to position their articulators correctly. They
visibly and audibly grope as they struggle to produce correct articulatory
postures and to accomplish a sequence of these postures in forming words. Their
articulation is frequently off target. They often recognise that they are off
target and effortfully try to correct the error.
Their errors recur, nonetheless, but they are not always the same; the errors
on a series of trials are highly variable. As patients struggle to avoid
articulatory error by careful programming of muscle movements, they slow down,
space their words and syllables evenly, and stress them equally. Thus the
prosody of their speech is altered as well as their articulation."
(Darley, Aronson, and Brown, 1975, p250)
Phoneme substitutions, additions, repetitions, and prolongations are common. Thus .....
"I
am looking an a drawring or a-a pec-picture of
what is apparently a tor-nuh-ner-nor-tornatiuhd blew-brewing in the c-countryside. This is
having an nuh-nuhmediate and
frightening ef-f-ff-fuh-feck on a fairm famerly num-ber-ing - - - six uh
humans and af-ff-sss-uh-sh-suh-sorted
farm uh animals. There are quick-uh-ly going into a-a sss-sor-sormb uh cellar with
fright in their ar-uh-eyes and in their every -
movement. (Darley, Aronson, and Brown, 1975, p250.
Underlines indicate errors and hyphens indicate hesitation.)
In the language of control theory, the suspicion is that a major feedforward mechanism is failing. Indeed, this underlies the distinction between planning and executive apraxias adopted by such authorities as Michael Crary of the University of Florida Health Science Centre, Gainesville. (Crary, 1993, with due acknowledgement to an earlier paper by Roy, 1978). The Roy-Crary scheme identifies four subtypes of the disorder .....
(a) Primary Planning
Dyspraxia: This is a high level
planning defect, and is usually associated with frontal lobe pathology.
(b) Secondary Planning
Dyspraxia: This is a lower level
planning defect - a defect of spatial organisation, perhaps, rather than an
inability to think ahead in its broadest sense. It is usually associated with
parietal-occipital pathology.
(c) Unit Dyspraxia: This is a defect which affects one particularly muscle
system more than the remainder.
(d) Executive Dyspraxia:
This is an inability to execute
movements which have successfully passed the planning stage. It is usually
associated with premotor area pathology. According to Roy: "..... although
the patient is able to plan the motor activity as the frontal areas are intact
and the pathways from the frontal to the premotor area are undisturbed, he is
unable to execute the movement sequence properly due to damage to the area
responsible for outputting the planned motor sequence" (Roy, 1978, p197).
Also from the University of Florida, Rothi and Heilman (1996) bring the story full circle by explicitly cross-mapping Liepmann's early descriptions onto a modern cognitive neuropsychological model (not dissimilar to our old friend, the PALPA model). The meaning of actions - that is to say, their utility to the organism in drawing up its plans - is seen as being mediated by a central "action semantics" store, whilst the supporting physical attributes are mediated by a secondary array of "action lexicons". It is a significant vindication of the transcoding school to find that their models - derived as they were from dyslexias and the like - can be applied just as effectively to human movement in its broadest form!
6.8 Dysarthria
of Speech
Before proceeding, students should refresh their memories
concerning the essentials of the motor system [revise it now].
Brainstem and cranial nerve anatomy [revise it now] is
particularly important, as is the differential layout of the pyramidal and
extrapyramidal systems!
Dysarthria of speech is the name given to speech difficulties arising from problems controlling the musculature involved. Some idea of the precision required can be gained from the fact that the tongue and lip movements in normal speech need to be coordinated to within 1/100th of a second and made to an accuracy of 1 mm (Netsell, 1986). So what happens when this accuracy of placing and timing starts to fall away? Well to start with .....
"In
dysarthria one finds evidence of slowness, weakness, incoordination, or change
of tone of the speech musculature. [All] basic motor processes - respiration,
phonation, resonance, articulation, and prosody - are variably involved. [The]
most characteristic error made by dysarthric patients
is imprecise production of consonants, usually in the form of distortions and
omissions." (Darley, Aronson, and Brown, 1975, p251.)
The situation is seriously complicated, however, because the motor mechanisms mentioned above (respiration, phonation, resonance, articulation, and prosody) are controlled by a minutely intricate arrangement of both spinal and cranial nerves. There are, as a result, several clinically distinct subtypes of dysarthria. Darley, Aronson, and Brown identify no less than six, as now described .....
(a) Flaccid Dysarthria: This type of dysarthria arises from damage at the
level of the lower motor neuron. Two clusters of lower motor neurons are
significant. Firstly, there are spinal nerve outflows from both thoracic
and lumbar regions. These innervate abdominal and intercostal muscles,
including the diaphragm, and thereby control the respiratory aspect of
phonation. Secondly, there are cranial nerve outflows from the lower
pons and the medulla. Of these, CN V (trigeminal), CN VII (facial), CN X (vagus), and CN XII (hypoglossal) have sensory and motor
functions in pharynx and jaw. Clinically, the salient features are muscle
weakness and hypotonia, and reduced or absent stretch
reflexes. The condition is found in the various subtypes of bulbar palsy
(depending on which of the cranial nerves is damaged). Speech presents as
"slow, hypernasal, and breathy, with reduced
loudness and reduced pitch variability" (Netsell,
1986, p41).
(b) Spastic Dysarthria: This type of dysarthria arises from damage at the
level of the upper motor neuron. As a result, lateralised lesions to
corticospinal tracts will present as contralateral defects, whilst those to
corticobulbar tracts (not fully decussating) will present as milder bilateral
weaknesses of tongue, lips, or face. The condition is found in what is known as
pseudobulbar palsy (bilateral corticobulbar damage at the level of the
upper motor neuron) and spastic hemiplegia. Speech presents as slow,
indistinct, and effortful, as though produced against resistance. The
descriptions "rasping" and "dragging" may also be
encountered.
(c) Ataxic Dysarthria: This type of dysarthria arises from damage to the
cerebellar system, most frequently bilaterally. The condition is found in, for
example, Friedreich's ataxia. The salient features are inaccuracy and
clumsiness of articulation, alternating with some staccato speech periods and
unexpected changes of pitch.
(d) Hypokinetic
Dysarthria: This type of dysarthria
arises from damage to the extrapyramidal system, thus implicating structures
such as the basal ganglia. Clinically, the salient features are slowness of
movement, limited range, rigidity, and tremor at rest. The condition is found
in Parkinson's disease and some Huntington's disease. Speech is
soft due to poor coordination of respiration and phonation, and wavering due to
inefficient vocal fold "hunting". When laryngeal closure eventually
fails totally, then all voicing is lost and only whispering is possible.
(e) Hyperkinetic
Dysarthria: This type of dysarthria
also arises from damage to the extrapyramidal system, but with a different set
of salient features, namely jerks, tics, chorea, ballism,
and athetosis. The condition is found in some Huntington's
disease, Tourette's syndrome, and Sydenham's chorea (more
commonly known as St Vitus' dance). Speech presents as hesitant and
randomly discontinuous due to disruption of orderly phonation.
(f) Mixed Dysarthrias: This
type of dysarthria arises from multifocal or diffuse lesions, that is to say,
those which damage more than one part of the motor system. The condition is
found in multiple sclerosis, and the symptoms are highly varied as a
result of the multifocal nature of the underlying pathology.
7 - Remarks
Finally, it is worth looking again at the speech
models identified in Section 4 in the light of the speech production defects
listed above. The anomias seem to be defects at or
around linguistic control level, either with having an idea in the first place,
or else with extracting an item from the semantic lexicon with which to express
that idea. The agrammatisms seem to be defects at or
around the lexical assembly area: the small clause as it is produced by
the linguistic controller is assumed to be inherently telegraphic at the best
of times, but in this particular type of defect is then denied further
expansion by defective morphological and syntactic assembly processes. The
jargons are defects across a somewhat broader spectrum: in all three subtypes,
it is as if (a) ideation itself is impaired, or (b) the linguistic controller
and sentence assembly processes are so impaired as to make it seem as though
ideation is impaired. The dyspraxias, too, can show
themselves at a number of levels along the planning-execution dimension, from
ideation at the top to phonetic planning at the bottom. And the dysarthrias are defects in execution, in either its
feedforward or feedback aspects. Note how difficult it is to locate the
defect accurately in most cases.
