Comodulation masking release for elderly listeners with relatively normal audiograms

Abstract

Thresholds for the detection of a 1.0-kHz pure tone were measured in modulated and unmodulated noise for a group of nine elderly listeners, aged 62-83, with normal or near-normal audiograms, and a reference group of seven younger normal-hearing listeners. The masker was either a band of noise 128 Hz wide [approximately one equivalent rectangular bandwidth (ERB) centered at 1.0 kHz], or a band of noise 1505 Hz wide (approximately five ERBs above and five ERBs below 1.0 kHz). The noise was either unmodulated or was square-wave modulated at rates of 10, 20, 30, 40, and 50 Hz. A measure of comodulation masking release (CMR) was derived from the masking data. Because wider filters have been found to be associated with reduced CMR, auditory filter shapes were also estimated for the elderly listeners. The filters were found to be normal at the center frequencies of 800, 1000, and 2000 Hz ruling out possible confounding effects of impaired auditory filters on CMR. Masked detection thresholds were generally significantly higher for the elderly as compared to the younger listeners for both unmodulated and modulated noise. Thresholds were lower in modulated as compared to unmodulated noise masking for both elderly and young listeners. For both groups of listeners and for both narrow- and wideband masking, detection thresholds continued to increase as modulation rates were increased. CMR was not different for the elderly and young listeners and it was similarly decreased, for both groups, at higher rates of modulation.