Abstract
In two experiments, we investigated the neural substrates that underlie difficult haptic discrimination of 3-D within-class object stimuli using fMRI. The stimuli were clay facemasks made from molds of real people's faces. Subjects were trained to haptically identify 18 clay facemasks and 18 control objects in the absence of vision. In Experiment 1, subjects haptically explored and silently named 12 facemasks and 12 control objects in a block-design imaging experiment. A statistical parametric map (SPM) comparing facemasks and control objects found more activation in the left fusiform gyrus with facemasks. In Experiment 2, subjects performed a haptic old/new recognition memory test on 12 trained and 12 untrained facemasks in an event-related design. A SPM comparing familiar and unfamiliar facemasks found more activation in the left fusiform gyrus with familiar facemasks. Finding evidence for left fusiform gyrus activation with haptically explored facemasks was surprising, given the reliability of right fusiform gyrus activation with visually explored face stimuli. As previously documented, haptic exploration of complex stimuli requires greater integration of features over time, whereas visual exploration requires greater integration of features over space. Also previously documented is a general functional lateralization in which left hemisphere functions are more sequential and right hemisphere functions are more spatial. Thus, activation in the fusiform gyrus may reflect this general functional lateralization applied specifically to the integration of object features.
Supported by CIHR (SJL,PS), NSERC (SJL,PS) and NSERC-PGB (ARK)