Event-related potentials and selective attention to auditory stimuli varying in pitch and localization.

Event-related potentials were recorded from subjects performing a discrimination task which required selective attention to one of (or divided attention to both of) two classes of tone pips imaged to arrive over two independent sound sources varying systematically in pitch and spatial localization. In selective attention N1 amplitude was larger and P2 amplitude was inversely smaller to the attended tones than to the unattended tones; P2 latency was prolonged to the attended tones; in divided attention, both N1 and P2 amplitudes and P2 latency were intermediate between selective attention and inattention. These attention effects upon both N1 and P2 components were interpreted to be due to a growth of a negative shift superimposed on those evoked components, rather than a modification of each component itself. This endogenous negativity was also considered to reflect the allocation of attentional capacity for discrimination processing whether tones coming from the attended source were 'signal' or not.