Reference no: EM133196593

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Case Study of a Category-Specific Deficit - Fur of the Crocodile and the Mooing Sheep

An important question for knowledge representation is "How are concepts organized?" Collins & Quillian proposed that knowledge could be represented in a hierarchical semantic network. A number of case studies provide support for this notion when deficits are seen for items in one category but not for items in a different category. The following citation is the source for the case study discussed here.

Kolinsky, R., Fery, P., Messina, D., Peretz, I., Evinck, S., Ventura, P., & Morais, J. (2002).

The fur of the crocodile and the mooing sheep: A study of a patient with a category-specific impairment for biological things. Cognitive Neuropsychology, 19 (4), 301-342.

ER suffered from herpes encephalitis. This resulted in what appears to be anterograde amnesia (much of his autobiographical memory prior to the herpes encephalitis seems to be intact but he is unable to recall new information). In addition to the amnesia, ER apparently has a difficult time recognizing biological items but no problem with non-biological items.

Table 1: Summary of a few of the results from Kolinsky et al. (2002) article. Percent correct naming of different types of images across three categories for patient, "ER," compared to normal control subjects.

	CATEGORY
TYPE OF TASK	Animals	Fruit/Vegetables	Artifacts(non-biological)
Naming Line Drawings
ER	33%	30%	71%
Control Group	98%	97.5%	99%
Naming Photographs
ER	50%	39%	82%
Control Groups	98%	97%	99%

The results indicate a consistent deficit for biological items (animal and fruit/vegetable categories) across a number of different tasks. Performance on artifacts (non-biological [e.g., anchor, alarm clock]) was consistently higher than the other two categories. The one exception to the biological deficit is the ability to recognize various human figures/body parts.

Summary of the case study by Kolinsky et al. (2002):

"We have documented here the case of a patient (ER) who displayed a category-specific deficit in recognizing biological entities. This impairment occurred across a variety of tasks and modalities, including recognition from vision, verbal definition, naming upon definition, drawing from memory, and nonverbal sound recognition. It can be explained by neither a perceptual deficit nor a lexical access deficit." (p. 331)

Often when ER was presented with a number of different tasks dealing with biological items, he would simply respond that he does not know or does not remember. However, there are times in which his responses consisted of confabulation. Confabulation was evident for biological items for visual and functional probes. The follow quote is confabulation for biological items (the authors noted that he did not do this with the non-biological category).

"The crocodile was thought to have fur ... The elephant was admitted to have horns ... The ostrich was said to be smaller than a hen, and the rhinoceros smaller than a lion. The giraffe was supposed to have short legs and the deer a long tail." (pp. 329-330)

Confabulation was evident for responses to nonperceptual characteristics of biological items.

"The lion and the rhinoceros were said to be nondangerous, but the deer to be dangerous 'for small animals that it may kill.' The penguin was supposed to live in the forest, and the zebra in cold countries; the mushroom was believed to grow in dry places and to be juicy. The frog was supposed to crawl, the snail to move fast, and the duck not to fly." (p. 330)

Discussion questions/topics:

1. Explain the results on the table.
2. What do the results of this case study suggest about the organization of information in memory?
3. Why do you think ER confabulated for certain types of information?
4. What was the goal of the researches when they tested ER with a variety of tasks (e.g., line drawings, pointing). The same deficit seems to appear across a number of different tasks.
5. What is the relevance of the information obtained from the control group?