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Abstract:
Previously (CNS, 1999) we reported that familiarity of
naturalistic sounds affected their electrophysiological correlates.
Novel sounds produced more negative waveforms than sounds rated as
familiar. Repetitions of both types of stimuli over a long delay
(100-110 items) resulted in a repetition effect consisting of more
positive waveforms beginning at about 450 milliseconds, but these
effects were attenuated for unfamiliar sounds. The current
experiment attempts to better characterize the repetition effects
for naturalistic sounds. 32-channels of event related potentials
(ERPs) were recorded while items were repeated at short (1-4 items)
and intermediate (40-70 items) lags, and subjects classified sounds
as familiar or unfamiliar. Repetition effects were observed at both
types of lags, but repetitions of unfamiliar items produced more
negative waveforms than repetitions of familiar items, even at the
short lags. For both familiar and unfamiliar sounds, repetition
effects appeared at all sites for the short lag but only at the
more posterior sites for the intermediate lag. For the unfamiliar
sounds this difference was most pronounced, with repetitions at
long lags actually producing more negative waveforms than their
first presentations. Results suggest that when delays are
substantial, repetitions only activate a posterior priming
mechanism. However, repetitions at shorter delays result in more
global priming effects. Familiar and unfamiliar items differ in
their degree of priming, but do not show evidence for qualitatively
different types of priming.
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