Ventral occipital lesions impair object recognition but not object‐directed grasping: an fMRI study

Abstract

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.

TMS can reveal contrasting functions of the dorsal and ventral visual processing streams

“…(Faillenot et al, 1997;James et al, 2003). These investigations indicate that object-oriented action and object recognition activate a common posterior parietal area.…”

Time course of the involvement of the ventral and dorsal visual processing streams in a visuospatial task

“…With respect to area V5, Schenk et al (2005) found that magnetic stimulation here can lengthen the execution of the action of catching a moving object. In contrast, a combined neuropsychological and fMRI study by James et al (2003) shows a clear dichotomy between the ventral and dorsal streams for object recognition and object directed grasping. Nevertheless, in normal human subjects a much more integrative approach may be involved in processing tasks like the present one, in which reciprocal interactions which involve earlier perceptual processes may be concerned either with perceptual issues or response issues in the task.…”

“…It is also possible that magnetically induced stimulation of both LO and PPC are impeding, and therefore slowing down, preparation for a motor response. The role of the dorsal stream in visuomotor transformations is clear from neuropsychological (James et al, 2003), functional imaging (Culham et al, 2006) and TMS (Ellison et al, 2003) studies. But this alone does not explain the involvement of PPC in the visuospatial task used in this study as PPC was not involved in a shape discrimination where the same visuomotor transformation was required in our previous paper (Ellison & Cowey 2006).…”

The fusiform face area is not sufficient for face recognition: Evidence from a patient with dense prosopagnosia and no occipital face area

“…Our research group had the opportunity to perform additional MRI and fMRI scans of D.F. in 2001 (Culham, 2004;James et al, 2003). An examination of the anatomical MRI images suggested three main lesions, one in the lateral occipital (LO) cortex of each hemisphere and one in the left hemisphere near the top of the parietooccipital sulcus.…”

“…An examination of the anatomical MRI images suggested three main lesions, one in the lateral occipital (LO) cortex of each hemisphere and one in the left hemisphere near the top of the parietooccipital sulcus. The location in stereotaxic space (Talairach & Tournoux, 1988) (James et al, 2003). Although D.F.…”