The Journal of the Acoustical Society of America vol:135 issue:4 pages:2412
Amplitude modulation is a common feature of natural sounds and an important cue in audition. Modulation supports perceptual segregation of "objects" in complex acoustic scenes, and provides information for speech understanding and pitch perception. Previous work in our laboratory showed increased modulation gain without change in temporal modulation transfer function (tMTF) bandwidth in auditory-nerve fiber responses to sinusoidal amplitude-modulated (SAM) tones measured in chinchillas with noise-induced hearing loss (HL), compared to normal-hearing (NH) controls. The ventral cochlear nucleus (VCN) provides significant input-output transformations with respect to amplitude-modulation representation, with enhanced spike synchrony to the amplitude envelope in several distinct cell types. We recorded spike times in response to SAM tones with modulation depths between 3% and 100% from all major VCN unit types in anesthetized NH and HL chinchillas. HL animals were previously exposed to 116 dBSPL 500 Hz-centered octave-band Gaussian noise. Spike times were analyzed in terms of synchrony to the amplitude envelope, tMTFs were calculated, and a signal-detection theoretic analysis was used to compute modulation-detection and discrimination thresholds. Results will be related to human perceptual studies, which have shown better modulation-detection thresholds in HL. [Work supported by an Action on Hearing Loss Fulbright Commission scholarship (M.S.), and NIH grant R01-DC009838.].