Wideband suppression in cochlear nucleus: a role in grouping by common onset?

Bleeck, S., Ingam, N., Verhey, J. and Winter, I.M. (2005) Wideband suppression in cochlear nucleus: a role in grouping by common onset? 28th Annual MidWinter Research Meeting, Association for Research in Otolaryngology, New Orleans, USA. 22 Feb 2005.

Abstract

Sounds that start at the same time are judged as originating from the same source. Darwin and Sutherland (Q. J. Exp. Psychol 1984. 36A , 193-208) demonstrated the effect of onset asynchrony: the perception of the vowel /I/ changes to /e/ by manipulating the harmonics around F1. Extending the augmented component before the vowel reduced this change. The change could be restored by using a "captor" tone which was switched on with the asynchronous harmonic but off when the vowel started. We hypothesise that (i) the reduced effect of the asynchronous component occurs because it has adapted before the other components begin (ii) a "captor" tone that groups with the leading segment reduces the neural response to that segment by activating an across-frequency inhibition from a wideband inhibitor (iii) the reduction in neural response is effectively a release from adaptation; (iv) the offset of the captor terminates the inhibition and the response to the continuation of that component is now enhanced and (v) because the captor offset occurs at the same time as the other components begin, all partials effectively have a common onset time, and so group together. As a preliminary test of the above hypothesis we measured the responses of single units in the cochlear nucleus of anesthetized guinea pigs to two-tone complexes. One tone was placed at the unit's best frequency (BF) while the second tone Ð the "captor" Ð was positioned in the unit's inhibitory sidebands. The captor tone was always turned off before the termination of the BF tone. For 36 units (n = 65) an increase in response to the BF tone was observed at the termination of the captor tone. This effect was most prominent in units classified as chopper and primary-like with a notch. These results suggest that wideband inhibition/suppression may play a role in grouping by common onset.

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Contributors

Author: S. Bleeck

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