Lateral occipito-temporal cortex involvement in haptic object recognition: evidence against mere visual imagery

摘要

Lateral occipito-temporal cortex (LOTC) participates in haptic object recognition but its role is controversial. We used fMRI to test whether or not its role is limited to visual imagery of object shape. Participants palpated recognizable objects using the right hand, with the hand positioned either to the right or left of the body midline. Position of fixation was varied across blocks, so that gaze direction was either straight ahead, to the left or to the right of body midline; palpated objects were always occluded from view. Our results showed that left LOTC was activated more strongly than right LOTC, even when participants palpated objects on the left side of the body, which suggests that LOTC represents objects with respect to the hand rather than side of body. LOTC activation was nevertheless modulated by side of palpation. Additionally, LOTC responses were modulated by gaze directiona??the strongest activation was observed when the location of the object was consistent with the direction of gaze (but not visible), although LOTC lateralization did not depend on the visual field location of the object. In contrast, activation in early visual cortex was best predicted by the visual field location of the palpated object (even though the object was hidden from view). Finally, somatosensory cortex and LOTC showed somewhat similar fMRI responses. If LOTC involvement in haptic object recognition reflects visual imagery, then LOTC lateralization should parallel that of early visual cortex. On the contrary, our findings suggest that LOTC encodes haptic shape cues in a hand-centered rather than body-centered coordinate frame, and thus LOTC activation during haptic object recognition is not indicative of potentially epiphenomenal visual imagery.