A dorsal visual route necessary for global form perception: evidence from neuropsychological fMRI.

Hierarchical models of visual processing assume that global pattern recognition is contingent on the progressive integration of local elements across larger spatial regions, operating from early through intermediate to higher-level cortical regions. Here, we present results from neuropsychological fMRI that refute such models. We report two patients, one with lesions to intermediate ventral regions and the other with damage around the intraparietal sulcus (IPS).

Deficits in visual search for conjunctions of motion and form after parietal damage but with spared hMT+/V5.

It has been argued that area hMT+/V5 in humans acts as a motion filter, enabling targets defined by a conjunction of motion and form to be efficiently selected. We present data indicating that (a) damage to parietal cortex leads to a selective problem in processing motion-form conjunctions, and (b) that the presence of a structurally and functional intact hMT+/V5 is not sufficient for efficient search for motion-form conjunctions. We suggest that, in addition to motion-processing areas (e.

Attention and its coupling to action.

We discuss two commentaries that we have received on our target article (Humphreys et al., 2010). We elaborate on the evidence for action effects on extinction and discuss whether these effects occur pre or post the selection of a response.

Neuropsychological evidence for a dissociation in counting and subitizing.

There is a long and ongoing debate about whether subitizing and counting are separable processes. In the present paper we report a single case, MH, who presents with a dissociation in subitizing and counting. MH was spared in his ability to enumerate small numbers accurately along with a marked inability to count larger numbers.

Impaired grasping in a patient with optic ataxia: primary visuomotor deficit or secondary consequence of misreaching?

Optic ataxia is defined as a spatial impairment of visually guided reaching, but it is typically accompanied by other visuomotor difficulties, notably a failure to scale the handgrip appropriately while reaching to grasp an object. This impaired grasping might reflect a primary visuomotor deficit, or it might be a secondary effect arising from the spatial uncertainty associated with poor reaching. To distinguish between these possibilities, we used a new paradigm to tease apart the proximal and distal components of prehension movements.