COCHLEAR MECHANISMS OF FREQUENCY AND INTENSITY CODING - II - DYNAMIC-RANGE AND THE CODE FOR LOUDNESS

Our preceding paper described SPL-dependenl changes in the shape of tr ansfer functions recorded from inner and outer hair cells as well as s upporting cells in the 500-2500 Hz regions of the Mongolian gerbil coc hlea. As SPL was increased, large shifts were observed in the peak of the transfer function. A strongly compressive nonlinearity was also ob served at CF. This paper examines the data from the perspective of int ensity coding in the auditory periphery. Based on the data, we offer a new explanation for the mechanisms underlying the different dynamic r anges of low and high threshold auditory neurons. We also find that, f or pure tone stimuli, the growth of excitation at the characteristic p lace saturates rapidly, and cannot encode the wide dynamic range of lo udness. The data are analyzed to explore other excitation pattern cand idates for loudness coding. The growth of the peak of the IHC transfer function, as well as the growth of the response area, have been found to be linearly related to loudness growth over most of its dynamic ra nge. Implications of the data for auditory intensity coding are discus sed. (C) 1998 Published by Elsevier Science B.V. All rights reserved.