Intensity discrimination of frozen and random noise bands

Abstract

This experiment examines how stimulus bandwidth and variability affect the difference limen, DL ( = 10*log[(I + ΔI)/I]), for a change in intensity. DLs were measured at 30, 60, and 90 dB SPL for a 3‐kHz tone and for nine noise bands with bandwidths ranging from 50 Hz to 12 kHz, using an adaptive two‐interval forced‐choice procedure. Results for three normal listeners show that the DLs are the same for frozen and random noise, except for the narrowest noise bands with steep skirts. For 50‐Hz bands, DLs for frozen noise decrease from about 3.5 to 1.2 dB as level increases from 30 to 90 dB, similar to DLs for the tone, but for random noise they are roughly constant, between 3 and 4 dB. Bandwidth has essentially no effect on the DLs at 90 dB, but at the lower levels the DLs decrease as bandwidth increases. An anomalous result is that the DLs are larger at 60 dB than at 30 dB for all bandwidths tested. The interaction of bandwidth and level is consistent with the excitation pattern model, but the effect of lev...