Attention affects the organization of auditory input associated with the mismatch negativity system

The mismatch negativity (MMN), a component of event-related potentials (ERP), was used to investigate the effect of attention on auditory stream segregation. Subjects were presented with sequences of alternating high and low tones that occurred at a constant rate, which they ignored. When subjects ignored the stimuli, the three-tone standard and deviant sequences contained within the high- and low-pitched tones did not emerge and no MMNs were obtained. Subjects were then instructed to attend to the high-pitched tones of the stimulus sequences and detect the within-stream deviants. When subjects selectively attended the high-pitched tones, MMNs were obtained to the deviants within both the attended and unattended streams. These results indicate that attention can produce segregation such that the sequences of low- and high-pitched tones are available to the automatic deviance detection system that underlies the generation of the MMN. Selective attention can alter the organization of sensory input in the early stages of acoustic processing.