The effects of between-source discriminability on attended and unattended auditory ERPs


  • This research was supported by an Australian Research Council Grant (A78615709) and a Macquarie University Research Grant.

  • We thank Allison Fox, Alan Taylor, and Brent Curtis for their technical assistance. A preliminary report of these data was presented at EPIC IX, Noordwijk, The Netherlands, May 1989.

Address requests for reprints to: Patricia T. Michie, School of Behavioural Sciences, Macquarie University, New South Wales, Australia 2109.


Event-related potentials (ERPs) for tone pips from attended and unattended sources, which varied on discriminability, were compared with ERPs for the same stimuli recorded during performance of a visual task. This comparison revealed that Nd, the negative shift of attended relative to unattended ERPs, consisted of three components: a negativity in the attended ERP from 100 to 270 ms, a positivity in the unattended ERP from 170 ms to the end of the epoch, and a second negativity in the attended ERP from 270 to 700 ms. In general, the later onset of early Nd with more difficult between-source discriminations could be attributed to the later onset of the positivity in unattended ERPs. A number of hypotheses were advanced for the origin of the unattended positivity: the suppression of the later of two negative components in the 100–220-ms range, an enhanced P2 component, an endogenous positivity, or the resolution of a protracted negativity elicited by preceding attended stimuli.