Studies using event-related potentials (ERPs) have shown that affectively arousing stimuli enhance attention and perception. In addition, simple neutral stimuli, when paired with emotionally engaging unconditioned stimuli (i.e., the CS+) in classical conditioning paradigms, were found to evoke increased sensory responses as learning progresses, compared to responses elicited by the same stimuli not paired with a noxious stimulus (CS-). To date the detailed trial-to-trial temporal dynamics of this sensory facilitation process is not known. Signal averaging required for the ERP analysis eliminates trial-to-trial information of temporal cortical dynamics. In the current study, a novel single-trial analysis method called Analysis of Single-trial ERP and Ongoing activity (ASEO) was adopted to study the detailed electrocortical dynamics of sensory processing during classical aversive conditioning. Focusing on the P1 component of the ERP evoked by simple grating patterns serving as CS+ and CS-, we found that over a session of conditioning trials, there were three phases of P1 amplitude changes for both CS+ and CS-: (1) an initial decrease phase, (2) a subsequent increase phase, and (3) a final habituating phase. Tests on the rates of P1 amplitude changes in each of the three phases between CS+ and CS- conditions revealed differential effects of CS+ and CS- for all three phases. No such effects were found for a session of control trials where the same grating patterns were paired with checkerboards. We interpret these results as providing evidence supporting the view that emotional experience can modulate early visual processing and dynamics of perceptual learning.
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