Loudness adaptation: further studies with the tracking method

Abstract

An experiment was conducted to determine if the duty cycle and period of a train of tone pulses presented simultaneously to the comparison ear influence in any way the adaptation measured at the opposite (test) ear. Eight normal-hearing listeners were adapted for 5 min to a steady 1-kHz pure tone at 60 dB SPL. Using a tracking procedure, adaptation over the 5-min period was measured under each of five comparison-signal conditions, each comprised of pulse trains having different on/off ratios. The five on/off ratios (in milliseconds) were: 200/800 (20% duty cycle); 500/500, 200/200, and 800/800 (50% duty cycle); and 800/200 (80% duty cycle). Listeners received each condition ten times. The comparison signals had a frequency of 1000 Hz. There was a clear tendency for adaptation to increase as the duty cycle of the comparison tone increased from 20% to 80%. This was evident even when attempts were made to take into account the extent to which the pulse trains might have been perceived as less loud than continuous signals at the same level (the so-called LOT effect). For comparison tones with a constant (50%) duty cycle, the same amount of test-ear adaptation was measured whether the on-time of the signals was 200, 500, or 800 msec. [Work supported by the Research and Education Committee, Oklahoma City Veteran's Administration Hospital, under Project No. 20-69.]