Binaural effects in center-frequency modulation detection interference forvowel formants

The detection of slow (5 Hz) center-frequency modulations of formants (sign als) can be impaired by the simultaneous presentation of off-frequency modu lated formants (maskers) to the same ear [J. Lyzenga and R. P. Carlyon, J. Acoust. Sec. Am. 105, 2792-2806 (1999)]. In the present study we examine th is "formant-frequency modulation detection interference (FMDI)" for various binaural masker presentation schemes. Signals and maskers were formantlike complex tones, centered around 1500 and 3000 Hz, respectively. Fundamental s of 80 and 240 Hz were used. The signals were presented to the right ear. The maskers were presented either to the right, the left, or to both cars, and they were either unmodulated or modulated at a slow rate (10 Hz). They had the same fundamental as the signals. Hardly any interference was found for the unmodulated maskers. For modulated maskers, the amount of FMDI depe nded strongly on the binaural masker presentation scheme. Substantial inter ference was found for the ipsilateral maskers. Interference was smaller for the contralateral maskers. In both cases the FMDI increased with increasin g masker level. Substantial interference was also found for the binaural ma skers. Imposing different interaural time and level differences (ITDs and I LDs) on maskers and signals did not affect FMDI. The same was true fur the ITD condition when the maskers had different fundamentals than the signals, though FMDI was slightly smaller here. The amount of interference for the binaural maskers was roughly equal to that of the corresponding monaural ma sker with the largest effect. The data could not be described accurately us ing a model based on the loudness of the maskers. On the other hand, they w ere well described by a model in which the amount of FMDI was predicted fro m a "weighted combination" of the monaural masker levels. (C) 2000 Acoustic al Society of America. [S0001-4966(00)03508-6].