The role of envelope fluctuations in an apparent demonstration of suppression in simultaneous masking

Beverly A. Wright*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

6 Scopus citations

Abstract

Fasti and Bechly [J. Acoust. Soc. Am. 74, 754-757 (1983)] reported that the threshold of a brief 900-Hz signal simultaneously masked by a band of noise, 100 Hz wide, centered at 1000 Hz, was reduced by approximately 8 dB by the addition of an 1150-Hz tone having a level of 20 dB above that of the narrow-band masker. They concluded that this decrease in threshold was a demonstration of suppression in simultaneous masking. Here it is argued that Fasti and Bechly's results simply reflect the poorer detectability of signals masked by higher-frequency fluctuating maskers (their narrow-band masker) than by relatively flat-envelope maskers (their composite narrow-band plus tonal masker). The results of three experiments support the masker-envelope explanation. In the first experiment, as in the report of Fasti and Bechly, the masker centered at 1000 Hz (Ml) was a narrow-band noise and the masker centered at 1150 Hz (M2) was a tone. Fasti and Bechly's result was replicated. However, thresholds obtained when Ml was presented alone (the Ml-only condition) were more affected by the starting level of the signal within each adaptive track than were thresholds obtained when Ml and M2 were presented together (the Ml + M2 condition). This result paralleled a previous report that starting level influenced performance more with fluctuating than with flat-envelope maskers. For the four of seven subjects who showed learning, there was also more improvement in the Ml-only than in the Ml + M2 condition. In the second experiment, Ml was a tone and M2 was a narrow-band noise. Thresholds were higher in the Ml + M2 than in the Ml-only condition, presumably due to the increased masker fluctuations in the Ml + M2 condition. Finally, in the third experiment, there was little or no difference in threshold in the Ml-only and Ml + M2 conditions for the majority of subjects when Ml and M2 were both tones. Caution is advised in interpreting a release from masking as suppression. The failure to demonstrate suppression in simultaneous masking for the majority of subjects, using an off-frequency signal and stimuli relatively free of the confounding influence of envelope fluctuations, is in contrast to a prediction that suppression in simultaneous masking should be revealed if the masker and signal have different frequencies and thus are not equally influenced by the suppression effect.

Original languageEnglish (US)
Pages (from-to)3436-3442
Number of pages7
JournalJournal of the Acoustical Society of America
Volume91
Issue number6
DOIs
StatePublished - Jan 1 1992

ASJC Scopus subject areas

  • Acoustics and Ultrasonics
  • Arts and Humanities (miscellaneous)

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