Dorsal and Ventral Cortical Pathways for Visuo-haptic Shape Integration Revealed Using fMRI

Visual object recognition is pervasive and central to many aspects of human functioning. In adults, it seems effortless and nearly automatic. Despite the ease with which we perceive and identify objects, however, computer simulations of object recognition have been largely unsuccessful at mimicking human recognition. Simulations can succeed in constrained environments, but cannot match the flexibility of the human system. One reason machine vision may have had limited success outside of highly constrained contexts is that visual recognition is an extremely difficult computational problem (Lennie, 1998). Another reason, however, may be that computational approaches have largely restricted themselves to modeling the visual system in isolation from other sensory and motor systems, whereas human visual recognition is embedded in interactions between multiple sensory systems (Clark, 1997; de Sa and Ballard, 1998). Although research of multisensory phenomena has a long history (Molyneux, 1688), research into the neural mechanisms of sensory processes in humans and other primates has been dominated in recent years by investigations of unisensory visual function. This has led to a relative paucity of empirical data from – and theoretical treatment of – other sensory systems and, perhaps most importantly, interactions between multiple sensory systems. Our goals in this chapter are twofold. First, we describe an influential theoretical perspective on the organization of the cortical visual system, the two visual streams theory, and apply that perspective to interactions between visual and haptic object shape processing. Second, using a new methodology, we assess neuronal convergence of visual and haptic inputs in regions considered part of those two separable pathways.