ASA 125th Meeting Ottawa 1993 May

4pPP4. Spectro-temporal enhancement measured by loudness matching.

Deborah A. Fantini

Dept. of Psychol., Essex Univ., Colchester CO4 3SQ, UK

Quentin Summerfield

Alan R. Palmer

MRC Inst. of Hear. Res., University Park, Nottingham NG7 2RD, UK

If one member of a series of equal-amplitude harmonics starts a few hundred milliseconds after the others, it may be ``enhanced'' and stand out perceptually. Viemeister and Bacon [J. Acoust. Soc. Am. 71, 1502--1507 (1982)] demonstrated that components produce more forward masking when enhanced than when present in a harmonic series without enhancement. Thus, enhancement appears to involve an increase in the internal level of a component. The present study was conducted to determine whether this result is also found in a loudness-matching task. Stimuli were derived from a harmonic series with a fundamental of 200 Hz. A 500-ms adaptor consisted of the series without the 1.8-, 2.0-, and 2.2-kHz components. A 100-ms standard included the 2-kHz component. Subjects heard the standard in the left ear followed by an identical 100-ms sound (the ``comparison'') in the right ear. They matched the loudness first of the background components and then of the 2-kHz component between the comparison and the standard. Preceding the standard by the adaptor reduced the loudness of the background components by 2 dB and raised the loudness of the 2-kHz component by 5 to 15 dB relative to the background components. Thus, loudness matching, like forward masking, demonstrates that enhancement increases the internal level of a component, but shows also that the levels of the background components are reduced.