The instruction to refrain from blinking affects auditory P3 and N1 amplitudes

Often subjects have been instructed to refrain from blinking lest their evoked EEG potentials should be distorted. We studied whether these very instructions have any impact on P3 amplitude. Two tones were presented in random order, and subjects had to count the high-pitched tones. Half the subjects were instructed not to blink, whereas this instruction was ommitted for the other subjects. Target tones evoked larger P3s than non-targets in the latter group but not in the former, in particular not in those subjects that actually blinked rarely. The groups also differed in their N1 amplitudes. These findings might be relevant to P3 studies working with patients and controls: the harder some frequently blinking subjects try to refrain from blinking, the smaller might become their P3 amplitudes. Omitting the instruction and using off-line blink subtraction procedures seems a viable alternative. This study was actually motivated by discrepant findings on the effects of the preceding tone sequence on P3. These discrepancies could be largely resolved by the instructional variable, in conjunction with different tone intensities. It is suggested that subjects who are discouraged from blinking try to protect themselves against the arousing effects of stimuli.