FAILURE OF OBJECT RECOGNITION DUE TO A BREAKDOWN OF FIGURE GROUND DISCRIMINATION IN A PATIENT WITH NORMAL ACUITY

We report the case of a 71-year-old woman with partial cortical blindness attributable to cortical degeneration. Her visual acuity and colour perception were satisfactory but she was almost totally unable to recognize objects or people by sight. Investigations revealed a hitherto unreported dissociation between relatively well preserved shape discrimination and gravely impaired figure-ground discrimination. Thus, she was able to discriminate between a square and an oblong matched for total surface but she was unable to detect a simple shape against a pattern background. In a series of experiments it was shown that she could identify single printed capital letters of the alphabet relatively satisfactorily. She had no difficulty in identifying single, simple geometric shapes. By contrast, she was unable to discriminate configurations of two or three overlapping or concentric, simple, shapes. Strikingly she appeared to be "blind" to subjective contours and she was unable to perceive visual illusions normally. These deficits are interpreted to reflect a failure to achieve primitive organization of visual information rather than higher level perceptual impairments. The results are discussed in the context of physiological and computational models of early visual information processing.