This review surveys the recent literature on visuo-haptic convergence in the perception of object form, with particular reference to the lateral occipital complex (LOC) and the intraparietal sulcus (IPS) and discusses how visual imagery or multisensory representations might underlie this convergence. Drawing on a recent distinction between object- and spatially-based visual imagery, we propose a putative model in which LOtv, a subregion of LOC, contains a modality-independent representation of geometric shape that can be accessed either bottom-up from direct sensory inputs or top-down from frontoparietal regions. We suggest that such access is modulated by object familiarity: spatial imagery may be more important for unfamiliar objects and involve IPS foci in facilitating somatosensory inputs to the LOC; by contrast, object imagery may be more critical for familiar objects, being reflected in prefrontal drive to the LOC.

Neuroimaging techniques have provided ample evidence for multisensory integration in humans. However, it is not clear whether this integration occurs at the neuronal level or whether it reXects areal convergence without such integration. To examine this issue as regards visuo-tactile object integration we used the repetition suppression eVect, also known as the fMRI-based adaptation paradigm (fMR-A). Under some assumptions, fMR-A can tag speciWc neuronal populations within an area and investigate their characteristics. This technique has been used extensively in unisensory studies. Here we applied it for the Wrst time to study multisensory integration and identiWed a network of occipital (LOtv and calcarine sulcus), parietal (aIPS), and prefrontal (precentral sulcus and the insula) areas all showing a clear crossmodal repetition suppression eVect. These results provide a crucial Wrst insight into the neuronal basis of visuo-haptic integration of objects in humans and highlight the power of using fMR-A to study multisensory integration using non-invasinve neuroimaging techniques.

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