Temporal masking curves and recovery from adaptation in hearing‐impaired listeners

Abstract

Temporal masking curves, obtained from 12 normal‐hearing and 16 hearing‐impaired listeners using 200‐ms, 1000‐Hz pure‐tone maskers and 20‐ms, 1000‐Hz fixed‐level probe tones, were fit by an exponential function with a single level‐independent time constant. Normal‐hearing listeners' time constants ranged between 37–67 ms, with a mean of 50 ms. Hearing‐impaired listeners' time constants ranged between 58–114 ms and increased exponentially with hearing loss according to the function τ = 52e0.011(HL), when the slope (k) of the growth of masking was restricted to unity. When iterative fitting procedures included k as a free parameter, k values from normal‐hearing listeners varied around unity (mean = 1.03), while those from hearing‐impaired listeners were less (mean = 0.71). These data indicate that temporal resolution is poorer in hearing impaired listeners by factors as large as 2.3 for a hearing loss of 52 dB, but the major effect of hearing loss on the detectability of sequential signals is due to the sensitivity loss and to an exponential recovery process that is dependent upon sensory response not stimulus level. In impaired ears, sensitivity loss apparently reduces the sensory response to high‐level maskers so that the recovery process is slower, much like it is for low‐level maskers in normal‐hearing listeners. [Work supported by NINCDS.]