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Abstract:
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 largely unknown. We addressed this question
in a combined fMRI and MEG study that made use of the high spatial resolution
of fMRI and the temporal resolution of MEG. 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 in each trial. To ensure
comparability between fMRI and MEG results, subjects participated in both parts of
the study. The fMRI results for 11 subjects 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 dierences in latencies
for the dierent ISIs across visual areas ranging between 70 and 160 ms. These
ndings 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 dierent temporal processing properties.
