JW is a relatively young man, in his early forties, who, despite many preserved cognitive abilities, fails to recognize many common objects. In August 1992, JW suffered a severe cardiac event while exercising and was subsequently anoxic. A computed tomography (CT) scan revealed multiple hypodensities in both occipital lobes with minor hypodensities in his right parietal lobe. Although JW has normal visual acuity as well as intact color and motion perception, Behrmann and colleagues have shown that he recognizes approximately 20% of black-and-white line drawings and a slightly higher percentage of color pictures. He is almost totally unable to recognize photographs of famous people. He is poor at copying simple line drawings presented to him (Fig. 1), at matching rectangles and squares of various dimensions, at simple shape detection (e.g., deciding that an "X" is present among a background of visual noise), and even at detecting symmetry in a visual image. Despite these impairments, he is able to recognize objects well from tactile/haptic input and from definitions that are read to him. These findings suggest that his long-term knowledge of objects is preserved. This is further confirmed by his ability to generate visual images in his ''mind's eye'' and to describe those in detail. Needless to say, this impairment significantly limits his ability to interact with objects and his world. Whereas JW was the owner of a hardware computer company (and had a master's degree in computer science), currently he works as a volunteer and provides instruction on computer use to people who are blind.
CK, like JW, is impaired at recognizing objects and has been studied extensively by Behrmann, Moscov-itch, and Winocur. CK sustained brain damage in a motor vehicle accident in 1988; he was struck on the head by the side mirror of a truck while he was jogging. Except for a hint of bilateral thinning in the occipito-temporal region, no obvious circumscribed lesion is revealed on magnetic resonance imaging (MRI) or CT scan. This may not be surprising given that his lesion was sustained via a closed head injury which often results in shearing of axons or more microscopic neuronal damage. Despite his deficits, CK functions well in his life; he has a responsible managerial job and makes use of sophisticated technology that allows him to translate written text into auditory output.
When asked to identify line drawings, CK misre-cognized a candle as a salt shaker, a tennis racquet as a fencer's mask, and a dart as a feather duster, presumably because of the feathers on the end (Fig. 2). As
JW's Copy Figure 1
Patient JW's copies of simple line drawings.
illustrated by these examples, CK, like JW, is clearly not blind. However, despite his intact visual acuity, he fails to recognize even familiar and common visually presented objects. This deficit holds irrespective of whether the objects are drawn in black-and-white on a piece of paper or whether they are shown in slides or even as real three-dimensional objects, although the addition of information such as color and surface texture does assist recognition to some extent.
CK, like JW, can also use tactile/haptic information to recognize objects; he was perfectly able to recognize a padlock and a paper clip by touch alone. CK can also provide detailed definitions for an object whose name is presented to him verbally; for example, he defined a pipe as ''a long cylindrical hollow object to convey liquid or gas'' and a card of matches as ''a cardboard container containing long sticks or matches which are struck against cordite.'' These definitions clearly demonstrate that his deficit is not attributable to a failure to name objects nor a loss of semantic knowledge.
CK is unable to read and, although he writes flawlessly, he cannot read his own writing presented to him at a later point in time. CK's hobbies have also
been affected; he is no longer able to design complex configurations of his large plastic soldier collection or visually differentiate airplanes, a domain in which he had rather extensive knowledge premorbidly.
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