Loudness adaptation and excitation patterns: effects of frequency and level.

Simple loudness adaptation for pure tones was measured at frequencies from 0.125 to 16 kHz and at sensation levels from 5 to 60 dB. Sixteen young listeners with normal hearing participated in four experiments. Most of the loudness measurements were obtained by the method of successive magnitude estimation; some were also obtained by loudness matching. The two indices of loudness adaptation gave similar results. At all frequencies, loudness adaptation increased as sensation level decreased. After 6 min, average loudness declined at most frequencies by about 20% at 40-dB sensation level (SL) and by between 70% and almost 100% at 5-dB SL. Adaptation also increased with increasing frequency, and was especially marked at 16 kHz, where loudness declined more than 60% at a sensation level as high as 40 dB. Most of the adaptation occurred usually within the first 3 min of exposure, but loudness continued to diminish at a slower rate up to around 6 min. The dependence of loudness adaptation on frequency and level can be largely accounted for by the restricted-excitation-pattern hypothesis. Adaptation is assumed to take place when excitation is restricted to a narrow region of the cochlea. This hypothesis is supported by a quantitative analysis based on excitation patterns derived from measurements of masking.