Intermodal selective attention: evidence for processing in tonotopic auditory fields.

Auditory event-related brain potentials (ERPs) were recorded for 250- and 4,000-Hz tone bursts in an intermodal selective attention task. Tonotopic changes were evident in the scalp distribution of the rising phase of the auditory N1 (mean peak latency 116 ms); the N1 was more frontally distributed following the 4,000-Hz than following the 250-Hz tone bursts, and it included a contralateral P90 component that was absent following 250-Hz tones. ERPs related to intermodal selective attention were isolated as negative and positive auditory difference waves (Ndas and Pdas). Neither the Nda nor the Pda showed changes in distribution with tone frequency, but both showed Ear x Frequency changes in distribution. ERPs for deviant tones included mismatch negativities (MMNs) and, in attend auditory conditions, N2b and P3 components. These components did not change in scalp distribution with tone frequency. One possible explanation is that tonotopic displacements of ERP distributions on the scalp surface depend on angular displacements in generator fields on gyral convexities. The results are consistent with the possibility that auditory processing radiates outward with increasing latency from tonotopic fields on Heschl's gyri to more gyrus-free regions of the planun temporale and anterior superior temporal plane.