Across-ear integration of acoustic-phonetic information under competitive conditions: Effects of attenuation increase in the presence of an extraneous formant

Abstract

Previous research using consonant-vowel syllables where one ear receives the first formant (F1) and the other receives the second and third has shown that dichotic release from masking allows F2 + F3 to remain effective speech cues even after substantial attenuation. This study used three-formant analogues of natural sentences and extended the approach to include competitive conditions. Target formants were presented dichotically (F1 + F3; F2), either alone or accompanied by an extraneous competitor for F2 (i.e., F1±F2C + F3; F2) that listeners must reject to optimize recognition. In experiment 1, F2C was absent and F2 was attenuated in 6-dB steps (range: -6-48 dB). Intelligibility was unaffected until attenuation >30 dB; F2 still provided useful information at 48-dB attenuation. In experiment 2, F2 was attenuated in 12-dB steps (range: 0-36 dB). F2C was created by inverting the F2 frequency contour and using the F2 amplitude contour without attenuation. When F2C was present, 12-dB attenuation was sufficient to cause some loss of intelligibility; the effect was large when attenuation ≥24 dB. This interaction suggests that some mandatory across-ear spectral integration occurs, such that informational masking arising from F2C rapidly swamps the acoustic-phonetic information carried by F2 as its relative level is attenuated. [Work supported by ESRC.]