ABSTRACT
There is growing research interest in the neural mechanisms underlying the recognition of material categories and properties. This research field, however, is relatively recent and limited compared to investigations of the neural mechanisms underlying object and scene category recognition. Motion is particularly important for the perception of non-rigid materials, but the neural basis of non-rigid material motion remains unexplored. Using fMRI we investigated whether brain regions respond differentially to material motion versus other motions. Stimuli were dynamic dot animations that induce vivid percepts of various materials in motion, e.g. flapping cloth, liquid waves, wobbling jelly. Control stimuli were scrambled motion and rigid three-dimensional rotating dots. We used a block design and the general linear model to contrast conditions (whole brain analyses). Results showed that isolating material motion properties with dynamic dots (in contrast with other kinds of motion) activates a network of activity in both ventral and dorsal visual pathways, including areas normally associated with the processing of surface properties and shape, and extending to somatosensory and premotor cortices. We suggest that such a widespread preference for material motion is due to strong associations between stimulus properties: when you see the dots move in a specific pattern not only do you see material motion – you see a flexible, non-rigid shape, identify the object as a cloth flapping in the wind, get a clear sense of its weight under gravity, and feel as though you could reach out and touch it. These results are a first important step in mapping out the cortical architecture and dynamics in material related motion processing.
