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Abstract:
This study investigated the extent to which complexity,
contextual deviance, and probability of appearence of visual
stimuli influence the N200 (peak negative wave 2--325 msec). 24
subjects participated in 3 event-related potential tasks. Each had
a repetitive background stimulus, an infrequent target stimulus,
and infrequent deviant stimuli. In Task A, all stimuli were simple
geometric figures. In Task B, all stimuli were unusual complex line
drawings and in Task C, background and target stimuli were complex,
while the deviant stimuli were simple geometric figures. Between
and within task analyses allowed us to address the impact of
complexity, deviance and infrequency, whil controlling for the
other factors. N2 amplitude was extremely sensitive to stimulus
complexity (e.g. N2 amplitude for Tasks B and C > Task; complet
deviants > simplet deviants (Task B vs. A, C); complex
backgrounds > simple backgrounds (Tasks B,C vs.A); complex
backgrounds > simple deviants (Task C)). Frequency of stimulus
presentation had little impact on N2 amplitude (e.g., infrequent
targets = frequent backgrounds (Task B); infrequent deviants or
targets = frequent backgrounds (Task A)). Contextual deviance also
had limited influence over N2 amplitude (seen only with complex
deviants > complex backgrounds at anterior, midline sites (Task
B)). We concluded that the visual N200 strongly indexes stimulus
complexity and unlike the visual P300 is realtivey insensitive to
stimulus probability and contextual deviance.
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