Lecturer's
Précis - Garrett (1990)
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First published online 14:30 BST 17th October 2002,
Copyright Derek J. Smith (Chartered Engineer). This version [2.0 - copyright] 09:00 BST 9th July
2018.
Although this paper is reasonably self-contained, it is best read as a subordinate file to our e-paper on "Speech Errors and Speech Production Models". An earlier version of this material appeared in Smith (1997; Chapter 6). It is repeated here with a colour-coded graphic and supported with hyperlinks. |
Garrett's
(1990) Model of Sentence Production
The University of Arizona's
Merrill F.
Garrett based his model of speech production on the sort of evidence
provided by speech error studies. He believes that a speaker's communicative
intention - the message - is input to a post-semantic speech production
system. Conventionally enough, he describes the first stage of this process as
obtaining some sort of word meaning record which does not yet include
information as to the final word form. He then concentrates upon the operations
which convert such messages into instructions capable (a) of initiating lexical
retrieval, and (b) of guiding the articulatory system. Errors can occur at
either stage: at the first stage they will be meaning-related, whilst at the
second stage they will be form-related.
Like the transcoding modellers, Garrett supports his theorising
with a dataflow diagram (DFD). There were several early attempts at such models
(eg. Garrett, 1975, 1980, 1982, 1984), but a more
up-to-date version is provided by Garrett (1990), in which he settles on a
five-level model of processing. There is one semantic level, namely the message
level, and four post-semantic levels, namely the functional, positional,
phonetic, and motor levels. These levels are described in the
caption box below:
Garrett's Speech Production Model: This model is a DFD with additional annotation, and
Garrett's explicit assumption is that "a speaker's particular
communicative intention [acts] as the input to the production system; we will
refer to that input as a message and the processes associated with it
as the Message level" (Garrett, 1990, p158; italics original).
Here are the processing levels identified: THE SEMANTIC LEVEL (THE COMPREHENSION
SYSTEM) Message Level
(M): This is the top level of
sentence construction, which Garrett groups together as "Inferential
Processes" [topmost mauve box]. This is the level at which the mind
somehow makes up its mind what it wants to say. It is the level of meaning,
and whenever an act of willed and meaningful communication is decided upon, a
suitably coded message, M, is passed downwards for
further action. THE POST-SEMANTIC LEVELS (THE PRODUCTION
SYSTEM) Functional
Level (F): This is where the
"phonologically uninterpreted" syntactic
relationship between words is determined. There are two sub-processes, lexical
selection and functional structuring, both colour-coded mid-blue. This level processes more than one, but probably
only two, phrases at a time (because word exchanges occur between adjacent
clauses, but rarely involve elements of non-adjacent clauses), and when
processing has been completed a functional level representation, F,
is passed down to the next level for further action. Positional
Level (P): This is where the surface
form of the sentence starts to appear, and matters of morphology, syntax, and
word order are sorted out. There are three sub-processes, word form
retrieval, positional planning, and node information, all
colour-coded light-blue. Garrett justifies this level being separate from the
functional level by referring to the phenomenon of accommodation in speech
errors. Thus if the message "a language acquisition device" were to
be articulated as "an anguage lacquisition device", the fact that the morpheme
"an" has replaced "a" correctly (but stupidly) indicates
that the allocation of "a" and "an" is normally made at a
later stage in production than word-building (morphology) or phrase-building
(syntax). The positional level is in fact the first of two levels at which
the final sound structure of the sentence starts to be determined. This level
deals with surface syntax, prosody, and abstract segmental and lexical
structure. It is seen as processing only one phrase at a time (which has
as-yet-unexplored implications for the feedback structure used), and when
processing has been completed a positional level representation, P,
is passed down to the next level for further action. Phonetic
Level: This is the second sound
structure level, and has been colour-coded lime. It deals with detailed
phonetic properties. Motor Level: This is the level of initiating actual muscular
activity, and has been colour-coded light lime. It is the level where the functional
motor systems communicate with the anatomical motor systems. Stripped of its annotation, the model
closely follows Lordat's (1943) "boxology" (Lecours, Nespoulos, and Pioger (1987).
Garrett's M-level is equivalent to Lordat's Stage
1, and Garrett's F, P, and Motor levels are Lordat's
Stages 2 to 4. Note the two major instances of parallel processing.
The first is where the message M simultaneously initiates both
word selection processes (upper left fork) and sentence structuring processes
(upper right fork). The second is where the functional level representation F
simultaneously initiates word form retrieval processes (lower left fork) and
clause structuring processes (lower right fork). If this diagram fails to load automatically,
it may be accessed separately at |
Developed from a black and white original in Garrett (1990:164), but with the Motor level, the italicised notes, and the colour coding added. This version Copyright © 2002, Derek J. Smith. |
That is the end of our
commentary. Now do the following exercise .....
Exercise to Consolidate Garrett (1990) suggests
that "the production system uses the comprehension system to monitor its
own products. We do listen to what we say ourselves, and we do this not only
to adjust the form of our utterance more closely to our communicative
objectives but also to monitor for error in the operation of the systems that
generate spoken form." (p166). However, the diagram includes none of the
feedback pathways by which this might take place. So ..... 1. Take a spare copy of the
Garrett model, and mark out all the feedback loops and servomechanisms you
can identify. 2. Mark the processing
carried out in parallel. 3. Dot in all possible additional feedforward and feedback loops (ie. those Garrett has omitted). |
For instructions on how to
build technically elegant DFDs, see our e-paper on
"How to Draw Cognitive Diagrams" or Smith
(1997; Chapter 3).
References
Garrett,
M.F. (1975). The analysis of sentence production. In
Bower, G.H. (Ed.), The Psychology of
Learning and Motivation (Volume 9). New York: Academic Press.
Garrett,
M.F. (1980). Levels of processing in sentence production. In
Butterworth, B. (Ed.), Language Production (Volume 1). Orlando,
FL: Academic Press.
Garrett,
M.F. (1982). Production of speech: Observations from normal and pathological
language use. In Ellis, A.W. (Ed.), Normality and
Pathology in Cognitive Functions. London: Academic Press.
Garrett,
M.F. (1984). The organisation of processing structure
for language production: Applications to aphasic speech. In
Caplan, D., Lecours, A.R., and Smith, A. (Eds.), Biological
Perspectives on Language. Cambridge, MA: MIT Press.
Garrett,
M.F. (1990) Sentence processing. In Osherson,
D.N. and Lasnik, H. (Eds.). An Invitation
to Cognitive Science (Volume 1): Language. Cambridge MA: MIT Press.
Lecours, A.R., Nespoulos, J.L., and Pioger, D.
(1987). Jacques Lordat, or the birth of cognitive neuropsychology. In Keller, E.
and Gopnik, M. (Eds.), Motor and Sensory Processes
in Language. Hillsdale, NJ: Erlbaum.
Smith,
D.J. (1997). Human Information Processing.
Cardiff: UWIC. [ISBN: 1900666081]