Feedback processing as parallel task in P300 conditioning

Previous reports on conditioning P300 amplitude indicated that downtraining produced a stronger effect than uptraining. This asymmetry can be due to t he effect of drain on processing resources of the brain produced by the att empts to use feedback information (parallel task effect). Such a drain shou ld reduce P300 amplitude regardless of the direction of training. The aim o f the experiment was to demonstrate this effect. Event related potentials ( ERPs) evoked by light stimuli in a standard odd-ball procedure were recorde d from Fz, Ct and Pt scalp sites. Subjects were instructed to enlarge or to reduce the P300 amplitude. The first 30 presentations of the target stimul us were analyzed during which the effect of learning should be negligible a nd processing of feedback information should be intensive. ERPs recorded du ring uptraining and downtraining were compared with the no-feedback recordi ngs. As predicted, downtraining significantly reduced the P300 amplitude ev en in the first session of learning. Unexpectedly, uptraining recordings di d not differ from no-feedback ERPs but differed significantly from downtrai ning waves. Such results support the prediction that feedback procedures in volve a number of processes that alter the P300 amplitude even before the e ffects of learning can be expected. But if the hypothesis of the parallel t ask is to be accepted there must be another instantaneous process that comp ensates for P300 amplitude reduction during uptraining.