Object adaptation in the lateral occipital complex: shape or semantics?

Unrestricted Changing object category from a cup to a violin produces a large release from adaptation in LOC (Grill-Spector, Kourtzi, & Kanwisher, 2001). However, without a principled way of measuring physical similarity, this effect could be due to either semantic or physical variations. In an fMRI-adaptation experiment, subjects viewed a sequence of two objects and judged whether the stimuli were identical in shape. Different-shaped stimuli could be from the same or different basic level classes, e.g., a poodle and a bulldog (Within class) vs. a poodle and a cat (Across class). The physical similarities of the stimulus pairs in the Within and Across conditions were equated with the Gabor-jet system (Lades et al., 1993), a model of simple cell similarity. BOLD responses in LOC for the Within and Across conditions were equivalent, and higher than that of the identical condition, suggesting that LOC is sensitive to shape rather than basic-level semantics.