Abstract
Knowledge of an object's material composition (i.e., what it is made of) alters how we interact with that object. Seeing the bright glint or hearing the metallic crinkle of a foil plate for example, confers information about that plate before we have even touched it. In a previous study (Cant & Goodale, 2007) it was shown that visually attending to an object's material properties as opposed to its shape or color, elicited greater hemodynamic activity in ventral occipitotemporal regions. In the present fMRI study, we investigated whether such areas are also sensitive to material properties of objects derived from sound only. Participants first completed a passive adaptation visual paradigm in which the material composition, shape or color of objects was manipulated in different blocks. In a separate series of blocks, participants were randomly presented with two-second normalized sound clips and asked to categorize them as either Material (crumpling styrofoam, plastic, tinfoil or paper), Noise (scrambled versions of each of the material sounds), or Human sounds (coughing, yawning, snoring or throat clearing). Replicating results from Cant & Goodale (2007), the visual task revealed a prominent area in the right parahippocampal region that was most selective for material as compared to shape or color properties. Although functional analyses of the auditory data within this visual material region did not reveal any discernable auditory modulation, expanding the region to include all of parahippocampal cortex revealed an area immediately adjacent to the visual material region that was highly selective for Material sounds as compared to Noise or Human sounds. Our findings point to an important multimodal role for the parahippocampal region in the analysis of material properties, and are in keeping with the notion that the medial aspect of the ventral pathway is specialized for processing the surface properties of objects.
Canadian Institutes of Health Research