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Abstract:
The second presentation of a visual stimulus produces less
activity in ventral occipito-temporal cortex (BA 19/37) compared
with initial viewing. Examining the effect of multiple
presentations with fMRI provides additional insight into this
priming phenomenon. Ten participants observed pictures of objects
during fMRI of occipital and temporal regions (1.5T Siemens Vision,
16-24x4mm axial slices, TR=2.0s). Each of 4-5 scanning runs
included 30 trials (ISI=12s) containing 4 targets and 6 run-unique
non-target stimuli presented 1-8 times in a simple target-detection
task (respond via button press: yes to the target object, no
otherwise). The stimulus-evoked response was estimated for all
non-target trials using individually assessed hemodynamic response
profiles (separate run, 5x4mm slices, TR=0.75s). Increased activity
was observed throughout occipital and ventral temporal visual
areas. On stimulus-repetition trials, reductions in activity were
evident across ventral occipito-temporal cortical areas. The
relationship between the evoked response and repetitions was fit
for linear and exponential functions. The exponential model fit
better in many areas, but additional areas exhibited a linear
decline in responses over 8 stimulus repetitions, possibly
reflecting different effects of priming within components of the
visual system. While interpretation of this quantitative technique
depends on the linear relationship between neural activity and
fMRI, the specific forms of the repetition/response curve provide
strong constraints for the development of neurally plausible
computational models of priming.
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