Novel hypotheses from a neuropsychological case study: is the visual ventral cortex critical for both category-generic and category-specific form perception?

Editor's Note: These short, critical reviews of recent papers in the Journal, written exclusively by graduate students or postdoctoral fellows, are intended to summarize the important findings of the paper and provide additional insight and commentary. For more information on the format and purpose of the Journal Club, please see Review of Karnath et al. In 1991, Milner et al. described a neuro-logical patient, D.F., who was able to calibrate precise movements toward objects but unable to perceive their visual forms. Despite being able to discriminate basic visual properties (e.g., color, intensity), she was impaired in perceiving geometric shape information and, as a consequence, also in object apperception (perceiving the structure of three-dimensional objects). This deficit is often termed visual form agnosia, to distinguish it from cases of impaired object apperception with intact shape perception (Milner et al., 1991). The observation of D.F. inspired the hugely influential " dual stream " model of visual cognition, which postulates independence between processing for perception in a " ventral " pathway and processing for action in a " dorsal " pathway. The dual stream model is also supported by further neuro-logical phenomena: in blindsight, the ven-tral stream is damaged at V1, causing a lack of conscious visual perception, yet patients show residual abilities for visually guided action ; in optic ataxia, the dorsal stream is damaged at the posterior parietal cortex, impairing visually guided action, yet visual perception is spared. The focus of D.F.'s cortical damage in the lateral occipital complex (LOC) of the ventral stream, bilaterally (see James et al., 2003), has led to the inference that the LOC is necessary for visual form perception. Furthermore, this conclusion is consistent with a wealth of more recent functional imaging studies of visual form perception in healthy subjects (Grill-Spector et al., 2001). However, Karnath et al. (2009) present an additional neurolog-ical case, patient J.S., with a behavioral profile similar to that of D.F. but with an intact LOC and damage to the nearby ventromedial occipitotemporal area bilaterally. This damaged area overlaps substantively with the visual ventral cortex (VVC), a region commonly associated with the apperception of particular categories of visual objects such as faces, places, and words (Haxby et al., 2001). In contrast, the LOC is implicated in visual form analysis at a category-independent stage of processing (Grill-Spector et al., 2001). Despite the known involvement of the VVC in object apperception, it is conceivable …