SPATIOTEMPORAL ENCODING OF SOUND LEVEL - MODELS FOR NORMAL ENCODING AND RECRUITMENT OF LOUDNESS

This study explores the hypothesis that sound level is encoded in the spatiotemporal response patterns of auditory nerve (AN) fibers. The te mporal properties of AN fiber responses depend upon sound level due to nonlinearities in the auditory periphery. In particular, the compress ive nonlinearity of the inner ear introduces systematic changes in the timing of the responses of AN fibers as a function of level. Changes in single fiber responses that depend upon both sound level and charac teristic frequency (CF) result in systematic changes in the spatiotemp oral response patterns across populations of AN fibers. This study inv estigates the changes in the spatiotemporal response patterns as a fun ction of level using a computational model for responses of low-freque ncy AN fibers. A mechanism that could extract information encoded in t his form is coincidence detection across AN fibers of different CFs. T his study shows that this mechanism could play a role in encoding of s ound level for simple and complex stimuli. The model demonstrates that this encoding scheme would be influenced by auditory pathology that a ffects the peripheral compressive nonlinearity in a way that is consis tent with the phenomenon of recruitment of loudness, which often accom panies sensorineural hearing loss.