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.)