Influence of duty cycle and off time of comparison-tone pulse trains on the measurement of perstimulatory loudness adaptation

An experiment was conducted to determine if duty cycle and off time of tone pulses presented to the comparison ear influence adaptation measured at the opposite (test) ear. Eight subjects were adapted for 5 min to a 1-kHz pure tone at 60 dB SPL. Using a tracking procedure, adaptation was measured under five comparison-signal conditions, each comprised of 1-kHz pulse trains having different on/off times. The on/off times (in milliseconds) were: 200/800 (20% duty cycle); 500/500, 200/200, and 800/800 (50% duty cycle); and 800/200 (80% duty cycle). Adaptation was found to increase as the duty cycle of the comparison tones increased from 20% to 80%. This was evident even when attempts were made to account for the extent to which pulse trains are perceived as softer than continuous signals at the same level (the so-called LOT effect). For the 50%-duty-cycle conditions, similar amounts of adaptation were measured whether the on/off times of the signals were 200, 500, or 800 msec.