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Abstract:
Abstract: Huettel and McCarthy (1999) showed that the
amplitude and latency of the hemodynamic response evoked by the
second of a pair of visual stimuli depended upon the duration of
the intra-pair interval (S1-S2 IPI). At 1sec IPI, the S2 response
amplitude was only 55% of the single-stimulus response; while the
S2 amplitude at 6sec IPI had recovered to 90%. These findings were
obtained in cortex adjacent to the calcarine sulcus using
full-field checkerboard stimuli; the current studies investigated
whether the rate of recovery varies across brain regions using more
complex visual stimuli. We presented faces either singly or in
pairs (IPIs of 1sec or 6sec). Coronal echo-planar fMRI slices
sampled the linear extent of the fusiform gyrus. The hemodynamic
response in the fusiform to S2 was attenuated in amplitude and
increased in latency at 1sec IPI, but recovered to near the
single-stimulus response by 6sec. However, anterior regions of the
fusiform exhibited less recovery than posterior regions. A control
experiment established that these anterior regions contained
proportionally more voxels that responded selectively to faces but
not to objects. Recovery in medial calcarine areas did not depend
on location of the activation. These results document a refractory
period in the hemodynamic response in both striate and
extra-striate cortex, although the characteristics of the
refractory period differ across brain regions.
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