Seeing Shapes and Hearing Textures: Two Neural Categories of Touch

Touching for shape recognition has been shown to activate occipital areas in addition to somatosensory areas. In this study we asked if this combination of somatosensory and other sensory processing areas also exist in other kinds of touch recognition. In particular, does touch for texture roughness matching activate other sensory processing areas apart from somatosensory areas? We addressed this question with functional magnetic resonance imaging (fMRI) using wooden abstract stimulus objects whose shape or texture were to be identified. The participants judged if pairs of objects had the same shape or the same texture. We found that the activated brain areas for texture and shape matching have similar underlying structures, a combination of the primary motor area and somatosensory areas. Areas associated with object-shape processing were activated between stimuli during shape matching and not texture roughness matching, while auditory areas were activated during encoding of texture and not for shape stimuli. Matching of textures also involves left BA47, an area associated with retrieval of relational information. We suggest that texture roughness is recognized in a framework of ordering. Left-lateralized activations favoring texture might reflect semantic processing associated with grading roughness quantitatively, as opposed to the more qualitative distinctions between shapes.