On the Relation Between Intensity Discrimination and Adaptation

Abstract

Increment detection was measured at 10 dB and 50 dB SL as a function of the delay between the onset of a continuous pedestal and the onset of a 50-ms increment. The effect of the delay depended both on frequency content and level of the signal. For a 4-kHz tone, detection (d' from a single-interval yes-no procedure) improved rapidly from about 1 s to 5 s; improvement continued even beyond 10 s, more so at 50 than at 10 dB. For a 500-Hz tone, detection did not improve with delay at either level. A broadband noise (20 Hz to 15 kHz) behaved at 10 dB like a 500-Hz tone–no improvement in detection with delay–and at 50 dB like a 4-kHz tone–strong improvement. Loudness measurements show that the effect of pedestal duration on increment detection does not result from loudness adaptation. Nonetheless, it would seem that the improvement in detection stems from long-term neural adaptation.