The relation between gap detection, loudness, and loudness growth in noise-masked normal-hearing listeners

Gap detection was measured for 50 and 1000-Hz-wide noise markers arithmetically centered on 1000 Hz. The markers were presented in a lowpass background noise having a high-frequency cutoff of 2000 Hz. The pressure spectrum level of the background noise was either 0 or 40 dB/Hz. Gap detection was determined at sensation levels (SLs) of 10, 15, 20, and 30 dB in the 0-dB/Hz background, and at SLs of 10, 15, and 20 dB in the 40-dB/Hz background. Because loudness increased more steeply in the higher level noise background, the markers in the 40-dB/Hz background were at higher loudness (and at a steeper portion of the loudness growth function) than markers in the 0-dB/Hz background, for markers matched in terms of SL. The main goal of the experiment was to determine whether gap detection would be relatively poor at steep portions of the loudness growth function due to the gap being confused with ongoing random dips. Such confusion might be particularly great when the noise bandwidth was narrow (and therefore characterized by prominent fluctuation) and the growth of loudness was steep. Gap detection was poorer for the 50-Hz-wide marker than for the 1000-Hz-wide marker. For a given marker bandwidth at a given SL, gap detection was similar whether the marker was presented in the 0-dB/Hz noise or the 40-dB/Hz noise. Supplementary conditions indicated that (1) gap detection results for 50-Hz-wide markers presented at equal SL's were also similar between a 0-dB/Hz noise background and a 55-dB/Hz noise background, and that (2) gap detection for 50- and 1000-Hz-wide markers was poorer in a 40-dB/Hz background than in a 0-dB/Hz background when markers were matched for loudness. The results generally indicated similar gap detection thresholds for markers presented at similar SLs across a relatively wide range of background noise levels. Gap detection was related more closely to the marker-to-noise ratio than to the loudness relation between markers or the steepness of loudness growth.