D.F., a patient with severe visual form agnosia, has been the subject of extensive research during the past decade. The fact that she could process visual input accurately for the purposes of guiding action despite being unable to perform visual discriminations on the same visual input inspired a novel interpretation of the functions of the two main cortical visual pathways or 'streams'. Within this theoretical context, the authors proposed that D.F. had suffered severe bilateral damage to her occipitotemporal visual system (the 'ventral stream'), while retaining the use of her occipitoparietal visual system (the 'dorsal stream'). The present paper reports a direct test of this idea, which was initially derived from purely behavioural data, before the advent of modern functional neuroimaging. We used functional MRI to examine activation in her ventral and dorsal streams during object recognition and object-directed grasping tasks. We found that D.F. showed no difference in activation when presented with line drawings of common objects compared with scrambled line drawings in the lateral occipital cortex (LO) of the ventral stream, an area that responded differentially to these stimuli in healthy individuals. Moreover, high-resolution anatomical MRI showed that her lesion corresponded bilaterally with the location of LO in healthy participants. The lack of activation with line drawings in D.F. mirrors her poor performance in identifying the objects depicted in the drawings. With coloured and greyscale pictures, stimuli that she can identify more often, D.F. did show some ventral-stream activation. These activations were, however, more widely distributed than those seen in control participants and did not include LO. In contrast to the absent or abnormal activation observed during these perceptual tasks, D.F. showed robust activation in the expected dorsal stream regions during object grasping, despite considerable atrophy in some regions of the parietal lobes. In particular, an area in the anterior intraparietal sulcus was activated more for grasping an object than for just reaching to that object, for both D.F. and controls. In conclusion, we have been able to confirm directly that D.F.'s visual form agnosia is associated with extensive damage to the ventral stream, and that her spared visuomotor skills are associated with visual processing in the dorsal stream.

In humans and many other primates, the visual system plays the major role in object recognition. But objects can also be recognized through haptic exploration, which uses our sense of touch. Nonetheless, it has been argued that the haptic system makes use of 'visual' processing to construct a representation of the object. To investigate possible interactions between the visual and haptic systems, we used functional magnetic resonance imaging to measure the effects of cross-modal haptic-to-visual priming on brain activation. Subjects studied three-dimensional novel clay objects either visually or haptically before entering the scanner. During scanning, subjects viewed visually primed, haptically primed, and non-primed objects. They also haptically explored non-primed objects. Visual and haptic exploration of non-primed objects produced significant activation in several brain regions, and produced overlapping activation in the middle occipital area (MO). Viewing visually and haptically primed objects produced more activation than viewing non-primed objects in both area MO and the lateral occipital area (LO). In summary, haptic exploration of novel three-dimensional objects produced activation, not only in somatosensory cortex, but also in areas of the occipital cortex associated with visual processing. Furthermore, previous haptic experience with these objects enhanced activation in visual areas when these same objects were subsequently viewed. Taken together, these results suggest that the object-representation systems of the ventral visual pathway are exploited for haptic object perception.

. (2006) 'The fusiform face area is not su cient for face recognition : evidence from a patient with dense prosopagnosia and no occipital face area.', Neuropsychologia., 44 (4). pp. 594-609. Use policyThe full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-pro t purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.Please consult the full DRO policy for further details.

Using fMRI, we showed that an area in the ventral temporo-occipital cortex (area vTO), which is part of the human homolog of the ventral stream of visual processing, exhibited priming for both identical and depth-rotated images of objects. This pattern of activation in area vTO corresponded to performance in a behavioral matching task. An area in the caudal part of the intraparietal sulcus (area cIPS) also showed priming, but only with identical images of objects. This dorsal-stream area treated rotated images as new objects. The difference in the pattern of priming-related activation in the two areas may reflect the respective roles of the ventral and dorsal streams in object recognition and object-directed action.

No abstract