اختلال در تصاویر چهره کمتر از ادراک صورت در پروزوپاگنوزیا اولیه

Abstract There have been a number of reports of preserved face imagery in prosopagnosia. We put this issue to experimental test by comparing the performance of MJH, a 34-year-old prosopagnosic since the age of 5, to controls on tasks where the participants had to judge faces of current celebrities, either in terms of overall similarity (Of Bette Midler, Hillary Clinton, and Diane Sawyer, whose face looks least like the other two?) or on individual features (Is Ronald Reagan’s nose pointy?). For each task, a performance measure reflecting the degree of agreement of each participant with the average of the others (not including MJH) was calculated. On the imagery versions of these tasks, MJH was within the lower range of the controls for the agreement measure (though significantly below the mean of the controls). When the same tasks were performed from pictures, agreement among the controls markedly increased whereas MJH’s performance was virtually unaffected, placing him well below the range of the controls. This pattern was also apparent with a test of facial features of emotion (Are the eyes wrinkled when someone is surprised?). On three non-face imagery tasks assessing color (What color is a football?), relative lengths of animal’s tails (Is a bear’s tail long in proportion to its body?), and mental size comparisons (What is bigger, a camel or a zebra?), MJH was within or close to the lower end of the normal range. As most of the celebrities became famous after the onset of MJH’s prosopagnosia, our confirmation of the reports of less impaired face imagery in some prosopagnosics cannot be attributed to pre-lesion storage. We speculate that face recognition, in contrast to object recognition, relies more heavily on a representation that descibes the initial spatial filter values so the metrics of the facial surface can be specified. If prosopagnosia is regarded as a form of simultanagnosia in which some of these filter values cannot be registered on any one encounter with a face, then multiple opportunities for repeated storage may partially compensate for the degraded representation on that single encounter. Imagery may allow access to this more complete representation.

Introduction Evidence from different domains of investigation suggests that visual imagery and visual perception share representations and processes (see [26] for a review). In the neuropsychological domain, cases of patients showing parallel impairments in imagery and perception have been considered as evidence that these activities share neural structures. However, dissociated impairments have also been reported, with individuals manifesting impaired perception with intact imagery [4] and [5] or vice versa [29] and [38]. Such observations have led some authors [5], [18], [26] and [27] to propose that although imagery and perception activate the same store of representations, they can differ in terms of processes. Parallel deficits in imagery and perception would result from impaired shared processes, such as those involved in accessing previously stored material. In contrast, isolated imagery deficits would result from impairment of processes specific to the imagery activity (such as the image generation processes) and isolated perceptual deficits would result from impairment of processes specific to the perceptual activity (such as edge detection and feature grouping). Imagery in individuals with a perceptual deficit could still be manifested by using visual representations processed and stored before the lesion occurred. In the face recognition domain, a few cases of preserved face imagery in prosopagnosia have been reported [3] and [15]. As expected from the standard account, these individuals could only imagine faces of persons learned before the lesion. Two broad types of prosopagnosia are usually distinguished: apperceptive (or perceptual) and associative (or mnesic) prosopagnosia [16]. Apperceptive prosopagnosia is defined by a perceptual deficit affecting the visual processing of faces. In associative prosopagnosia the deficit is at the memory level: faces can be correctly processed but associated information (personality, name, etc.) can no longer be retrieved. As Young et al. [43] suggest, only patients with apperceptive agnosia may show preserved face imagery. Patients with associative prosopagnosia could not access visual representations of faces from names. In this study, we report the case of an apperceptive prosopagnosic patient, MJH, whose pattern of performance—less impaired imagery, relative to his perceptual recognition, of faces acquired after the onset of his prosopagnosia—is not readily, prima facia, reconciled with the standard accounts of the relation between perception and imagery. We do, however, offer a speculation as to how these results might be accommodated by a general model of face representation.

14. Conclusions To conclude, we reported the case of a prosopagnosic who has some imagery for faces that he has difficulty perceiving. These are faces that he would not have learned prior to his lesion. This a priori paradoxical pattern of results is explained in the context of a new account of prosopagnosia in which only subsets of Gabor jets can be represented during perception. We propose that these partial percepts can be improved in memory through the error correction afforded through repeated exposures to the face. This improved memorial representation would allow a prosopagnosic patient to visualize faces encountered after the onset of the lesion.