The enhancement effect is consistently shown when simultaneously masked stimuli are preceded by the masker alone, with a reduction in the amount of masking relative to when that precursor is absent. One explanation for this effect proposed by Viemeister and Bacon (1982). J. Acoust. Soc. Am. 71, 1502-1507 is the adaptation of inhibition, which predicts that an enhanced component (the target) will be effectively more intense within the auditory system than one that has not been enhanced. Forward masking studies have indicated this effect of increased gain; however, other explanations of the enhancement effect have also been suggested. In order to provide an alternative measure of the amount of effective gain for an enhanced target, a subjective binaural centering task was used in which listeners matched the intensities of enhanced and unenhanced 2-kHz tones presented to opposite ears to produce a centered stimulus. The results showed that the enhancement effect produces an effective 4-5 dB increase in the level of the enhanced target. The enhancement effect was also measured using other enhancement paradigms which yielded similar results over a range of levels for the target, supporting an account based on adaptation of inhibition.
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The authors would like to thank Dr. Christopher Plack, Dr. Quentin Summerfield, and an anonymous reviewer who provided helpful comments and suggestions for improving this manuscript. This work was supported by Research Grant No. R01 DC 00683 from the National Institute on Deafness and Communication Disorders, National Institutes of Health.
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