Journal of cognitive neuroscience
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Abstract We have previously reported that a patient (DF) with visual form agnosia shows accurate guidance of hand and finger movements with respect to the size, orientation, and shape of the objects to which her movements are directed. Despite this, she is unable to indicate any knowledge about these object properties. In the present study, we investigated the extent to which DF is able to use visual shape or pattern to guide her hand movements. ⋯ Little evidence was found for an ability to use contour boundaries defined by Gestalt principles of grouping (good continuation or similarity) or "nonaccidental" image properties (colinearity) to guide her movements. We have argued elsewhere that the dorsal visual pathway from occipital to parietal cortex may underlie these preserved visuomotor skills in DF. If so, the limitations in her ability to use different kinds of "pattern" information to guide her hand rotation suggest that such information may need to be transmitted from the ventral visual stream to these parietal areas to enable the full range of prehensive acts in the intact individual.
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A spurious category-specific visual agnosia for living things in normal human and nonhuman primates.
Abstract Patients with visual associative agnosia have a particular difficulty in identifying visually presented living things (plants and animals) as opposed to nonliving things. It has been claimed that this effect cannot be explained by differences in the inherent visual discriminability of living and nonliving things. To test this claim further, we performed two experiments with normal subjects. ⋯ They made many more errors in discriminating among living things than nonliving things. Agnosic patients' responses to the same line drawings were made available to us for correlative analysis with the subjects' responses to these drawings in Experiments 1 and 2. We conclude that a category-specific visual agnosia for living things can arise as a consequence of a modality-specific but not category-specific impairment in visual representation, since living things are more similar to each other visually than nonliving things are.