Results from research on slow cortical potentials, especially CNV research, suggest that attention may be increased with increased cortical negative shifts. The present study investigates the relationship between performance in a signal detection task and slow cortical potentials. Cortical shifts were varied by means of a biofeedback procedure. 22 subjects received continuous visual feedback or their slow cortical potentials (SCP) during intervals of 6 sec, 11 yoked control subjects received "false feedback" of the SCP of a matched experimental partner. Minimal changes of the feedback stimulus presented for 100 msec at different times during the feedback interval served as signals to be detected. The experiment consisted of 240 trials. Experimental subjects learned to shift their cortical level towards more or less negativity or positivity depending on the frequency of a signal tone. Mean differences were, however, small (5 >iV) compared to previous results on self-regulation of SCP. All subjects showed a P300 if a signal was detected correctly, whereas no positive wave occurred if "false alarms" were made. Experimental subjects showed a highly significant inverted U-shaped relationship between SCP-shift and signal detection performance, i.e., were better during small negative shifts than during strong negative or small positive shifts. No relationship was found in yoked control subjects who also showed no variation of SCP. Furthermore, yoked control subjects showed a performance decrement compared to experimental subjects. It is suggested that a shifting of cortical potentials facilitates attentional processes. The lack of a systematic variation of SCP in yoked control subjects also may be responsible for the lack of relationship between SCP and signal detection performance in yoked control subjects.
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