Abstract
Differences in ear of presentation and level do not prevent effective integration of concurrent speech cues such as formant frequencies. For example, presenting the higher formants of a consonant-vowel syllable in the opposite ear to the first formant protects them from upward spread of masking, allowing them to remain effective speech cues even after substantial attenuation. This study used three-formant (F1+F2+F3) 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. F2C was created by inverting the F2 frequency contour and using the F2 amplitude contour without attenuation. In experiment 1, F2C was always absent and intelligibility was unaffected until F2 attenuation exceeded 30 dB; F2 still provided useful information at 48-dB attenuation. In experiment 2, attenuating F2 by 24 dB caused considerable loss of intelligibility when F2C was present, but had no effect in its absence. Factors likely to contribute to this interaction include informational masking from F2C acting to swamp the acoustic-phonetic information carried by F2, and interaural inhibition from F2C acting to reduce the effective level of F2.
Highlights
Listeners are capable of combining the acoustic-phonetic information carried by formants with different excitation source properties, such as differences in fundamental frequency (F0; e.g., Cutting, 1976) or stimuli for which some formants are rendered as buzz-excited resonances and others as sine-wave analogues (Roberts et al, 2015; Summers et al, 2016)
Rand (1974) attributed this outcome to dichotic release of the higher formants from energetic masking by the more intense F1. These findings suggest that when energetic masking is limited or prevented—whether by within-ear spectral distance or presentation to opposite ears—the tendency to combine acoustic-phonetic information across formants over a wide range of levels may be a general characteristic of speech perception, at least when there is only one message present
In experiment 1, and the study reported by Rand (1974), optimal performance required the listener to integrate across ears the acoustic-phonetic information carried by all the formants presented
Summary
Rand (1974) attributed this outcome to dichotic release of the higher formants from energetic masking by the more intense F1 These findings suggest that when energetic masking is limited or prevented—whether by within-ear spectral distance or presentation to opposite ears—the tendency to combine acoustic-phonetic information across formants over a wide range of levels may be a general characteristic of speech perception, at least when there is only one message present. The generality of this suggestion is explored in the current study by addressing two important questions arising from limitations of previous research on the effects of changes in relative formant amplitude on speech perception.
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