Psychometric amplitude-modulation detection thresholds in chinchillas before and after moderate noise exposure

Abstract

Recent findings from animal studies suggest that moderate-level acoustic overexposure can produce permanent cochlear synaptopathy while not significantly affecting hearing thresholds in quiet. It has been hypothesized that this hidden hearing loss may underlie difficulties some listeners have in noisy situations even with normal audiograms. However, this hypothesis has not been tested directly due to difficulties measuring behavior in animal models for which cochlear synaptopathy has been demonstrated, and the inability to measure cochlear synaptopathy directly in humans. We recently established a mammalian model (chinchilla) that has corresponding neural and behavioral amplitude-modulation (AM) detection thresholds in line with human behavioral thresholds, and which shows cochlear synaptopathy following moderate noise exposure. Here, behavioral AM-detection thresholds were measured in six chinchillas, before and after noise exposure, using the method of constant stimuli. Animals were trained to discriminate a sinusoidal AM (SAM) tone (4-kHz carrier) from a pure tone, in the presence of a notched-noise masker. Behavioral thresholds before noise exposure were consistent across individual animals and were in the range from -25 to -15 dB. Preliminary data collected following noise exposure do not show a substantial effect on AM-detection thresholds in this simple task. [Work supported by NIH grant R01-DC009838.]