Lecturer's Précis - Warrington and
McCarthy (1987)
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First published online 09:00 GMT 11th February 2004, Copyright Derek J.
Smith (Chartered Engineer). This version
[HT.1 - transfer of copyright] dated 12:00 13th January 2010
Warrington and
McCarthy (1987) on "Categories of Knowledge"
Warrington and McCarthy (1987) report clinical case study material on YOT, a 50-year-old right-handed female, who suffered a stroke in August 1984 which blocked her left middle cerebral artery. Initially she suffered a global aphasia [glossary], but as this started to resolve it left a curious category-specific impairment [glossary], "namely the preservation of animals, foods, and flower names" (p1275).
Now it happens that relatively "pure" impairments such as this are rare in the literature. Nielson (1958) found only 15 prior reports, six of patients with a selective knowledge of living things, and nine of patients with a selective knowledge of man-made objects. Moreover, Warrington and McCarthy had themselves reported on an earlier patient, VER, in whom the "verbal knowledge of common objects" (Warrington and McCarthy, 1983, p1278) had been impaired but the knowledge of animals, foods, and flower names preserved. They were accordingly keen to investigate what might prove to be a "double dissociation" [glossary], and YOT's deficit was therefore explored in detail, using a number of specially designed tests as follows .....
Experiment 1 - Animals, Flowers , and Objects: An array of pictorial stimuli was prepared,
consisting of five flower, five animal, and five object pictures. Correct
identification was scored using a matching-to-sample technique [glossary], by having YOT select her answer manually from a
desktop array of alternative pictures, rather than verbally. The actual test
items were .....
nettles, buttercup, thistle, rose, daffodil
tiger, camel, monkey, giraffe, zebra
scissors, steps, fork, mop, hammer
Correct
responses were obtained on 86% of the flowers and animals, compared to only 67%
on the objects (p<0.01).
Experiment 2 - Foods, Animals, and Objects; Slow or Fast Response: Using now three blocks of five pictures in each
category (rather than a single block of five as above), and replacing flowers
by foods (eg. sprouts, beans, milk, etc.), the test was repeated for
both two-second and five-second response-stimulus intervals (RSI). All three
categories performed at about 90% or better in the five-second condition, as
did food and animals in the two-second condition. However, performance with
objects in the two-second condition ran at only 60%. In other words, "there
was no category effect whatsoever with the slower RSI" (p1279). Warrington
and McCarthy therefore suspected that YOT had difficulty "accessing
semantic information rather than in the absolute loss or degradation of the
semantic representation per se" (p1280) [hence the descriptor "access
dysphasia" in their 1983 paper].
Experiment 3 - Foods, Manipulable Objects, and Large Man-Made Objects: This experiment introduced picture sets for two
fundamental categories of object, namely small manipulable objects (eg. chair,
cup, belt, shoe) and large man-made objects (eg. ship, train, pier,
windmill). Correct response selection was 83% on foods and 78% on large
objects, but only 58% on smaller objects.
Experiment 4 - "Fine-Grain" Category Specificity: It had already been noted that YOT was able to match
printed words to their pictorial equivalents, so this experiment set out to
test her ability to match spoken words to their printed equivalents. Stimulus
sets were prepared for 16 knowledge sub-categories. YOT's performance was
"remarkably satisfactory" (80% or better) for animals, occupations,
vegetables, and fabrics, intermediate (60% to 79%) for types of accommodation,
fruit, clothing, transport, and colours, and poor (59% or worse) for flowers,
geographical features, kitchen utensils, weather, office stationery, furniture
(22%), and parts of the body (19%).
ASIDE: Kay, Ellis, and Coltheart's (1992) PALPA diagram was not, of course, available in 1987, and so
Warrington and McCarthy were unable in this write-up to track the corresponding
cognitive processing against that diagram. It is, however, highly informative
to do so in retrospect [and readers unfamiliar with the diagram in question
should print themselves off a copy and follow with their fingers the routes now
discussed]. The point is that the act of matching a spoken word to its printed
equivalent requires the coordinated activity of many cognitive subprocesses. To
begin with, the spoken word must pass through the upper left processing
quadrant, passing through AUDITORY PHONOLOGICAL ANALYSIS to the PHONOLOGICAL
INPUT BUFFER, from where it is matched against the contents of the PHONOLOGICAL
INPUT LEXICON [glossary]
before being passed to the SEMANTIC SYSTEM for interpretation. It is
then necessary to scan the array of possible printed words, passing each one
through the upper right processing quadrant until one is found which activates
the same lexical and semantic entries as the target word had done. This is a
complex piece of processing, and offers many points where categorial coding
might be implicated.
Experiment 5 - Category Specificity for Proper Nouns: This experiment was designed to test YOT's
comprehension for subcategories of proper nouns. Stimulus sets were prepared
for 12 subcategorical knowledge areas. Results showed "remarkable
preservation" for the comprehension of famous people (100%), countries
(88%), and cities (88%), intermediate performance for sports (77%) and emotions
(61%), and poor performance for units of time (50%), parts of a house (44%),
girls' names (38%), musical instruments (33%), academic subjects (27%),
surnames (22%), and boys' names (17%, the chance level). As to why this should
be, McCarthy and Warrington suggest that the critical variable is whether the
target name has or does not have a unique referent [ie. there is only one
"Winston Churchill" but there are many "Davids"]. This
particular pattern of impairment had not, to the authors' knowledge, been
observed previously.
Experiment 6 - The Effects of Semantic Similarity: This experiment set out to test YOT's ability to
process semantic similarity. Stimulus sets were prepared for six of YOT's impaired
categories (namely office stationery, household items, clothes, kitchen
utensils, furniture, and parts of the body) and six of the preserved ones
(namely countries, famous people, famous buildings, occupations, transport, and
geographical features). Within each set, there were six stimulus items, and
these were arranged either as semantically "close" or semantically
"distant". For the semantically close condition, all six items in the
test array were from the same category, and for the semantically distant
condition, all six items were from different categories. These stimuli were
then presented in spoken word or written word form for a picture-matching
response. Results for the spoken word presentation condition showed performance
"at ceiling" for the preserved categories, with only a small effect
of semantic distance (close = 92%, distant = 97%; not significant). For the
impaired category, however, the distance effect was more pronounced (close =
47%, distant = 79%; p<0.05).
Warrington and McCarthy summarise the issues as follows .....
"In
this series of experiments we have documented the residual comprehension
abilities of a patient YOT who had a severe global aphasia such that her
capacity for comprehension and production of propositional speech appeared to
be virtually absent. Nevertheless, using matching to sample techniques [glossary],
we were able to document islands of preserved comprehension." (Warrington
and McCarthy, 1987, p1286)
..... and concluded that YOT's basic problem was accessing semantic material, not its unavailability per se. Thus .....
"We
have characterised an access deficit in terms of inconsistency in the
availability of a particular representation over time. It differs from a degradation
deficit in which the central representation itself appears to be damaged."
(Warrington and McCarthy, 1987, p1286; italics original.)
References
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