Temporal properties of shape processing across visual areas: A combined fMRI and MEG study

Recent studies have shown that global information about shapes is processed in both early ventral (i.e. V1, V2, Vp, V4) and higher occipitotemporal visual areas (i.e. Lateral Occipital Complex-LOC). However, the temporal properties of shape processing across visual areas in the human brain are not known. We addressed this question in a combined fMRI and MEG study that made use of the complimentary spatial and temporal resolution of the two techniques. We used an event-related adaptation paradigm in which lower neural responses are observed for two identical than two different consecutively-presented stimuli. The stimuli were closed contours that consisted of collinear Gabor elements. We manipulated the interstimulus interval (ISI: 100 vs. 400 msec) between the two consecutively-presented stimuli. The fMRI results showed adaptation for both the short and the long ISI in the LOC but only for the short ISI in early visual areas. The MEG data showed similar patterns of response amplitude to the fMRI data and differences in latencies for the different ISIs across visual areas. These findings suggest sustained shape processing in higher visual areas compared to more transient visual analysis in early visual areas. Further studies test the analysis of local vs. global shape features across areas with different temporal processing properties.