Seeing the eyes in acquired prosopagnosia.

Case reports have suggested that perception of the eye region may be impaired more than that of other facial regions in acquired prosopagnosia. However, it is unclear how frequently this occurs, whether such impairments are specific to a certain anatomic subtype of prosopagnosia, and whether these impairments are related to changes in the scanning of faces. We studied a large cohort of 11 subjects with this rare disorder, who had a variety of occipitotemporal or anterior temporal lesions, both unilateral and bilateral. Lesions were characterized by functional and structural imaging. Subjects performed a perceptual discrimination test in which they had to discriminate changes in feature position, shape, or external contour. Test conditions were manipulated to stress focused or divided attention across the whole face. In a second experiment we recorded eye movements while subjects performed a face memory task. We found that greater impairment for eye processing was more typical of subjects with occipitotemporal lesions than those with anterior temporal lesions. This eye selectivity was evident for both eye position and shape, with no evidence of an upper/lower difference for external contour. A greater impairment for eye processing was more apparent under attentionally more demanding conditions. Despite these perceptual deficits, most subjects showed a normal tendency to scan the eyes more than the mouth. We conclude that occipitotemporal lesions are associated with a partially selective processing loss for eye information and that this deficit may be linked to loss of the right fusiform face area, which has been shown to have activity patterns that emphasize the eye region.

Voice Recognition in Face-Blind Patients.

Right or bilateral anterior temporal damage can impair face recognition, but whether this is an associative variant of prosopagnosia or part of a multimodal disorder of person recognition is an unsettled question, with implications for cognitive and neuroanatomic models of person recognition. We assessed voice perception and short-term recognition of recently heard voices in 10 subjects with impaired face recognition acquired after cerebral lesions. All 4 subjects with apperceptive prosopagnosia due to lesions limited to fusiform cortex had intact voice discrimination and recognition. One subject with bilateral fusiform and anterior temporal lesions had a combined apperceptive prosopagnosia and apperceptive phonagnosia, the first such described case. Deficits indicating a multimodal syndrome of person recognition were found only in 2 subjects with bilateral anterior temporal lesions. All 3 subjects with right anterior temporal lesions had normal voice perception and recognition, 2 of whom performed normally on perceptual discrimination of faces. This confirms that such lesions can cause a modality-specific associative prosopagnosia.

Word and text processing in acquired prosopagnosia.

OBJECTIVE: A novel hypothesis of object recognition asserts that multiple regions are engaged in processing an object type, and that cerebral regions participate in processing multiple types of objects. In particular, for high-level expert processing, it proposes shared rather than dedicated resources for word and face perception, and predicts that prosopagnosic subjects would have minor deficits in visual word processing, and alexic subjects would have subtle impairments in face perception. In this study, we evaluated whether prosopagnosic subjects had deficits in processing either the word content or the style of visual text. METHODS: Eleven prosopagnosic subjects, 6 with unilateral right lesions and 5 with bilateral lesions, participated. In the first study, we evaluated their word length effect in reading single words. In the second study, we assessed their time and accuracy for sorting text by word content independent of style, and for sorting text by handwriting or font style independent of word content. RESULTS: Only subjects with bilateral lesions showed mildly elevated word length effects. Subjects were not slowed in sorting text by word content, but were nearly uniformly impaired in accuracy for sorting text by style. INTERPRETATION: Our results show that prosopagnosic subjects are impaired not only in face recognition but also in perceiving stylistic aspects of text. This supports a modified version of the many-to-many hypothesis that incorporates hemispheric specialization for processing different aspects of visual text.

Learning to read upside-down: a study of perceptual expertise and its acquisition.

Reading is an expert visual and ocular motor function, learned mainly in a single orientation. Characterizing the features of this expertise can be accomplished by contrasts between reading of normal and inverted text, in which perceptual but not linguistic factors are altered. Our goal was to examine this inversion effect in healthy subjects reading text, to derive behavioral and ocular motor markers of perceptual expertise in reading, and to study these parameters before and after training with inverted reading. Seven subjects engaged in a 10-week program of 30 half-hour sessions of reading inverted text. Before and after training, we assessed reading of upright and inverted single words for response time and word-length effects, as well as reading of paragraphs for time required, accuracy, and ocular motor parameters. Before training, inverted reading was characterized by long reading times and large word-length effects, with eye movements showing more and longer fixations, more and smaller forward saccades, and more regressive saccades. Training partially reversed many of these effects in single word and text reading, with the best gains occurring in reading aloud time and proportion of regressive saccades and the least change in forward saccade amplitude. We conclude that reading speed and ocular motor parameters can serve as markers of perceptual expertise during reading and that training with inverted text over 10 weeks results in significant gains of reading expertise in this unfamiliar orientation. This approach may be useful in the rehabilitation of patients with hemianopic dyslexia.