Auditory facilitation: procedural or sensory effect?

Abstract

A few studies have reported that, under certain conditions, thresholds following exposure to a sound may be lower than those measured without prior stimulation. For example, Rubin [J. Acoust. Soc. Am. 32, 670-681 (1960)] found a 7-dB negative shift in threshold, for a 20-ms tone presented 160 ms after termination of a low-level cue tone. This "auditory facilitation" was obtained with an up-and-down psychophysical method. In the present study, auditory facilitation was reexamined using an adaptive, two-interval, two-alternative-forced-choice (2I, 2AFC) procedure. Thresholds were measured for 20-ms tones at 1 and 5 kHz, preceded by a 15-dB SL 80-ms cue tone of the same frequency. In addition, thresholds were measured with the cue absent. The results show that thresholds can be lower in the presence of the cue than in its absence, but the effect averages 0.5 dB or less and seems to be independent of cue-signal delay between 80 and 640 ms. Because this finding contrasts with the 7-dB facilitation, which Rubin obtained using an up-and-down method, part of his experiment was replicated and the results were essentially the same as his. The failure to find a pronounced facilitation effect with a 2I, 2AFC procedure indicates that the poststimulatory lowering of threshold found by Rubin primarily resulted from biases and criterion shifts.