When Leopards Lose Their Spots: Knowledge of Visual Properties in Category-specific Deficits for Living Things

Abstract

Several cases of category-specific semantic deficits for living things have now been reported, most of whom have a greater difficulty with knowledg e of visual properties of living things than with non-visual properties. This has motivated two different kinds of account of category-specific deficits for living things. One account is that the impairment for living things arises as a result of general damage to visual properties, and so it predicts that impairment for visual properties of living things will be accompanied by some degree of impairment for visual properties of other categories. The second account posits explicit category-based organisation of semantic memory, such that visual properties of living and non-living things are stored separately, and so can be independently impaired. We investigated the semantic impairment of a patient SE, who had received a diagnosis of herpes simplex encephalitis several years previously, resulting in a mild category-specific semantic deficit for living things. Both off-line and on-line tasks revealed that SE had a highly selective impairment for the visual properties of living things, with no sign of problems for the visual properties of non-living things. This raises a challenge for models in which category-specific deficits emerge as a result of a general deficit determined by some other factor. We suggest one way in which these models may account for the data by encoding inter-relations between the function and form of objects in semantic memory.

Conceptual Structure and the Structure of Concepts: A Distributed Account of Category-Specific Deficits

“…Detailed investigations of patterns of impaired and preserved semantic knowledge demonstrated by such patients provide invaluable insights into the way in which semantic information is stored and accessed. One especially important source of data comes from patients with what appear to be ''category-specific deficits''; selective impairments restricted to specific domains or categories of semantic knowledge (e.g., de Renzi & Lucchelli, 1994;Farah, McMullen, & Meyer, 1991;Hart & Gordon, 1992;Hillis & Caramazza, 1991;Moss, Tyler, & Jennings, 1997;Sacchett & Humphreys, 1992;Sartori & Job, 1988;Warrington & McCarthy, 1983;1987;Warrington & Shallice, 1984; for a review see Saffran & Schwartz, 1992). The most frequently observed pattern is that knowledge of living things is impaired with knowledge of artifacts relatively preserved, although the reverse pattern has occasionally been reported (Hillis & Caramazza, 1991;Sacchett & Humphreys, 1992;Warrington & McCarthy, 1983, 1987.…”

The fur of the crocodile and the mooing sheep: A study of a patient with a category-specific impairment for biological things

“…Similarly, in comparison to artefacts, he was still impaired on highly typical biological items corresponding to frequent, early acquired words. Thus, the impact of factors like familiarity, typicality, and word frequency, although significant, cannot fully account for ER's impairment.As in many previous similar case studies (Basso, Capitani, & Laiacona, 1988;Breedin, Saffran, & Coslett, 1992;Damasio, 1990; De Renzi & Luchelli, 1994;Forde et al, 1997;Hillis & Caramazza, 1991;Moss, Tyler, & Jennings, 1997;Sheridan & Humphreys, 1993;Silveri & Gainotti, 1988;Swales & Johnson, 1992;Warrington & Shallice, 1984), ER's impairment for biological things was not absolute. Indeed, he was able to recognise or name some of the line drawings and pictures of animals, fruits, vegetables, and food items, and, for unrecognised items, he displayed preserved information about superordinate category.…”

“…Among his errors preserving superordinate information, although non-recognition was more frequent than misrecognition for biological items, the reverse occurred for artefacts. In addition, human figures and body parts yielded perfect scores (e.g., Hart & Gordon, 1992;Hillis & Caramazza, 1991;Moss et al, 1997).…”

“…For example, it is not obvious how the sensory/functional theory would make sense of some attested patterns of associations and dissociations of category-specific deficits, i.e., of a truly selective deficit for the visual properties of biological things unaccompanied by any degree of impairment for those of nonbiological things , or of a selective deficit for the nonvisual, associative knowledge of biological things (Laws et al, 1995; but see Moss et al, 1997). Caramazza and Shelton (1998) listed additional arguments against the sensory/functional hypothesis.…”

“…Among his errors preserving superordinate information, although non-recognition was more frequent than misrecognition for biological items, the reverse occurred for artefacts. In addition, human figures and body parts yielded perfect scores (e.g., Hart & Gordon, 1992;Hillis & Caramazza, 1991;Moss et al, 1997).Finally, ER's impairment was not limited to lexical access, given that it remained when descriptions suggesting object recognition were taken into account. However, in order to assess more precisely the patient's ability to access semantic information from visual information in the absence of name production requirement, we presented him with word-drawing matching and semantic association tasks.…”