Preserved visual imagery and categorization in a case of associative visual agnosia.

A patient with associative visual agnosia secondary to a penetrating bitemporooccipital lesion remained able to draw complex objects from memory but could not subsequently recognize his sketches. His retained ability to copy and draw briefly exposed objects indicates that this is not a problem of visual perception. On tasks of categorization, mental imagery, drawing, and object decision, he demonstrates many instances of preserved visual semantic memories and imagery despite a sense of unfamiliarity with the visual stimuli. We infer a preserved ability to derive internal visual images from semantic memory. Cues may help him visualize the named object, which then serves as a model for comparison with the actual stimulus. However, his adequate visual perception and mental visual imagery, even when assisted by cues, are still insufficient to correct fully his difficulty in recognizing objects. Unique to his case is an inability to match the representation of stimulus objects with his intact internal image of the same object. Deficient lateral inhibition between neural representations of similar objects may be responsible.