fMRI-derived cortical maps for haptic shape, texture, and hardness.

We used functional magnetic resonance imaging (fMRI) to investigate the neural substrates involved in haptic processing of texture, shape, and hardness. Subjects performed haptic classification tasks on a set of 27 silicone objects having parametrically defined shape, texture, and hardness. The objects were ellipsoids of revolution in which the ratio of the long to the short axis was varied, producing three different shapes. Three surface textures and three hardness levels were used. In three separate experiments, the same subjects classified each object along the three levels of one of the object properties (shape, texture, or hardness). Texture, shape, and hardness processing led to contralateral activation in the postcentral gyrus (PCG). A common region located within relatively posterior portions of the PCG was observed during shape and texture identification whereas a separate and more anterior region was activated during the hardness identification task. The hardness identification task also produced bilateral activation within the parietal operculum.