An fMRI investigation of visual, tactile and visuo-tactile “what” and “where” dissociations

Visual information about the shape and location of objects is processed with different but interrelated pathways. Considerably less is understood about the existence of similar pathways in the tactile domain and how the tactile and visual domains converge to form a coherent multisensory percept. The present fMRI study was conducted to determine how the tactile and visual modalities interact during both shape ("what") and location ("where") tasks. In the visual-visual condition, the "what" task activated a large number of brain areas not observed in the "where" task including hippocampus, fusiform and lingual gyrus, middle and inferior frontal gyri. No additional brain areas were stimulated in the "where" than "what" tasks suggesting that "where" tasks recruit a subset of those brain areas involved in matching information relating to identity. In contrast, activity during the tactile-tactile condition differed according to task. Activity during the "what" task was greater in the right superior temporal gyrus, and during the "where" task in the left inferior parietal lobule. Brain areas activated during visuo-tactile object recognition included areas previously implicated in visuo-tactile object matching tasks. These areas were not similarly active during the visuo-tactile "where" task suggesting they may be specific for crossmodal object recognition.