Frequency Discrimination in Noise

Abstract

Frequency DLs were obtained near masked threshold (1–15 dB SL) at 250, 1000, and 4000 Hz. Three spectrum levels (31.5, 51.5, and 71.5 dB) were used. An adaptive sequential procedure based on 4IFC was used in estimating ΔF. Also, two signal modes were used. In one, the pulsed tone presented during the “signal interval” was frequency modulated. In the other, the pulsed tone presented during the “signal interval” was a steady, but different, frequency. Characteristic improvement was seen at all frequencies when ΔF was plotted as a function of sensation level. At 4000 Hz, however, a significant “noise-level” effect was noted, in which discrimination at the 51.5-dB spectrum level (band level of 86 dB) was poorer than that for 31.5 and 71.5 dB. This “noise-level” effect was essentially the same for both modes of signal presentation. While this effect is difficult to explain in psychophysical terms, the literature on physiological acoustics offers some promise of accounting for it.