Slow negative shifts of the human event-related potential associated with selective information processing.

Event-related potentials (ERPs) to random sequences of tones delivered to the right and left ears were recorded during a pitch discrimination task which required subjects to attend selectively to one ear at a time and respond to occasional 'target' tones in that ear. The morphology of a long-lasting negative shift, arising before the N1 peak and locating over frontal region in ERPs to the attended 'standard' tones with reference to those of the unattended standards, was investigated under different stimulus conditions. When slight pitch changes of targets were presented in the first 40 msec portion of the 240 msec stimulus duration, the largest development of the attention-related negativity was observed earlier than when presented in the last portion of the duration. The results are interpreted as supporting the view that the negativity reflects further processing carried out on each relevant input after that input is identified.