This study employed behavioral and electrophysiological measures to examine selective listening of concurrent auditory stimuli. Stimuli consisted of four compound sounds, each created by mixing a pure tone with filtered noise bands at a signal-to-noise ratio of +15 dB. The pure tones and filtered noise bands each contained two levels of pitch. Two separate conditions were created; the background stimuli varied randomly or were held constant. In separate blocks, participants were asked to judge the pitch of tones or the pitch of filtered noise in the compound stimuli. Behavioral data consistently showed lower sensitivity and longer response times for classification of filtered noise when compared with classification of tones. However, differential effects were observed in the peak components of auditory event-related potentials (ERPs). Relative to tone classification, the P1 and N1 amplitudes were enhanced during the more difficult noise classification task in both test conditions, but the peak latencies were shorter for P1 and longer for N1 during noise classification. Moreover, a significant interaction between condition and task was seen for the P2. The results suggest that the essential ERP components for the same compound auditory stimuli are modulated by listeners' focus on specific aspects of information in the stimuli.
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We would like to thank Liz Tusler, Tess Koerner, Asher Miller, Kayla Kelsey, Jason Sumontha and Dr. Edward Carney for their assistance in data collection. Thanks to Dr. Robert D. Melara and two anonymous reviewers for providing invaluable suggestions to improve this manuscript. Rao gratefully acknowledges financial support from the American Speech-Language-Hearing Foundation and the University of Minnesota . Zhang acknowledges lab startup funds from the University of Minnesota, Brain Imaging Research Awards (2008 and 2009) from the College of Liberal Arts, and support from CLA Associate Dean, Dr. Jo-Ida Hansen.
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