Small pitch separation and the selective-attention effect on the ERP

In conditions demanding selective attention, the stimuli to be attended elicit an event-related brain potential (ERP) component called the processing negativity (PN). However, some previous results might be interpreted as suggesting that even the stimuli to be ignored elicit some PN, at least if they physically resemble those to be attended. This 'generalization' of PN was studied by presenting three equiprobable tones differing in pitch in random order, one of the tones at a time being the target to be counted. The small pitch separation between the three tones was of different magnitude in different blocks. A PN was observed in the ERPs to the counted stimuli but was even elicited, though with a smaller amplitude, by the nontargets, at least by those which physically resembled the targets. The latter, 'generalized' PN was larger in amplitude with a smaller pitch separation between the nontarget and target stimulus. These results support the interpretation that PN reflects a cerebral matching process between the sensory input and a voluntarily maintained neuronal representation of the stimulus to be attended, the 'attentional trace'. Moreover, these results indicate rather high discrimination accuracy of this stimulus-selection mechanism underlying PN.