The physiological mechanisms for encoding high-frequency spectral information at high levels.

High frequency spectral notches generated by the filtering action of the pinna are important cues for sound localization. Phase locking is absent in the response of auditory nerve fibers for frequencies above approximately 4 kHz. Therefore, high-frequency spectral notches must be encoded in the rate response of auditory nerve fibers. However, the rate-response representation of these notches degrades for high stimulus levels. This has been attributed to two factors: a) basilar-membrane filters get broader at high levels; and b) most nerve fibers have a narrow dynamic range.This yields some doubts as to whether spectral notches are perceived at high levels (e.g. Lopez-Poveda, 1996). The purpose of our work is to investigate the extent to which this true.

Selected publications:

Lopez-Poveda, EA, and Meddis, R.  (1996).  «A physical model of sound diffraction and reflections in the human concha,» J. Acoust. Soc. Am. 100, 3248-3259.

Alves-Pinto, A., and Lopez-Poveda, E.A. (2005). «Detection of high-frequency spectral notches as a function of level,» J. Acoust. Soc. Am. 118, 2458-2469.

Alves-Pinto, A., Lopez-Poveda, E.A., and Palmer, A. R. (2005). «Auditory nerve encoding of high-frequency spectral information,» in IWINAC 2005, J. Mira and J.R. Alvarez (Eds.), Lecture Notes in Computer Science 3561, 223-232.

Lopez-Poveda EA, Alves-Pinto A, Palmer AR. (2007) «Psychophysical and physiological assessment of the representation of high-frecuency spectral notches in the auditory nerve,» in Hearing: From Sensory Processing to Perception, edited by B Kollmeier, G Klump, V Hohmann, U Langemann, M Mauermann, S Uppenkamp, J Verhey.  Springer-Verlag, Heidelberg. pp. 51-59.