Rate encoding of binaurally alternating low-frequency tone bursts in macaque A1

Abstract

Integration of sequential components is an essential feature of auditory scene analysis. Humans consistently underestimate by 35–50% the frequency (F) of click trains, when the component clicks alternate between ears, and F exceeds 10 Hz [Axelrod et al., J. Acoust. Soc. Am. 43, 51–55 (1968)]. This suggests a boundary for integration of sequential components. Multiunit Activity (MUA) and current source density (CSD) in A1 of the awake monkey were used to explore neural correlates of this illusion. Phase-locked responses of cortical neuronal ensembles correlate with the perceptions of human listeners [Soc. Neurosci. Abstr. 22:637.18 (1996)]. Above 10 Hz, inhibition in thalamorecipient layers suppressed the response to each ipsilateral click in the train, in regions of high best frequency (BF). Here these observations are extended to low BF sites, which respond poorly to clicks. Responses to 25-ms low-frequency alternating tone bursts exhibit a boundary above 10 Hz, in agreement with click train data. The consistency of this physiologic boundary across the tonotopic map of A1 may represent an important neural substrate for assigning individual components to perceptual streams. [Work supported by DC00657 and the Institute for Music and Neurologic Function of Beth Abraham Hospital.]