Selective attention and the auditory vertex potential. II. Effects of signal intensity and masking noise

Abstract

A randomized sequence of tone bursts was delivered to subjects at short inter-stimulus intervals (mean ISI of 333 msec), with the tones originating from one of three spatially and frequency-specific channels. The subject's task was to count the tones in one of the three channels at a time, ignoring the other two, and press a button after each tenth tone. In different conditions, tones were given at high (60 dB SL) and low (20 dB SL) intensities and with or without a background white noise to mask the tones. The N 1 component of the auditory vertex potential was found to be larger in response to attended-channel tones than in relation to unattended tones. This selective enhancement of N 1 was minimal for loud tones presented without noise and increased markedly for the lower tone intensity and in noise-added conditions. The selectivity of attention as measured physiologically in this multichannel listening task was thus greater when tones were faint and/or difficult to detect.