Auditory Masking and the Critical Band

TLDR

Masked audiograms were measured across bandwidth, level, and frequency of masking noise, and a reverse procedure used a movable narrow‑band signal amid masking tones to determine audiograms. The study found that bandwidth‑dependent changes in masked audiograms enabled measurement of critical bandwidth, while discontinuities at a transition level (~50 dB SL) in audiogram height, shape, and the appearance of a notch one critical bandwidth above a masking tone indicated the critical band and possibly the inner‑hair‑cell threshold.

Abstract

Masked audiograms were studied as a function of the bandwidth, level, and frequency of a masking noise. In a reverse procedure, audiograms were determined when a movable, narrow, and approximately rectangular band of noise was used as signal in the presence of one or more masking tones. In both cases changes in the masked audiograms as a function of bandwidth made it possible to measure critical bandwidth. When masked audiograms were studied as a function of level, discontinuous changes in their height and shape occurred when the masking stimulus reached a certain “transition” level. If masking noises of subcritical or critical width were used, the growth of masking with level contained a discontinuity at a level of the masking stimulus equal to about 50 db SL. An abrupt change in the shape of the masked audiograms occurred at the same level. The change of shape when a pure tone was the masking stimulus consisted in the appearance of a “notch” one critical bandwidth above the frequency of the masking tone. Findings associated with the bandwidth parameter suggest interpretations of the critical band and of masking. The changes occurring at the transition level may indicate the threshold of the inner haircells.