Limits on phonetic integration in duplex perception

Abstract

The telling fact about duplex perception is that listeners integrate into a unitary phonetic percept signals that are coherent from a phonetic point of view, even though the signals are, on purely auditory grounds, separate sources. Here we explore the limits on the integration of a sinusoidal consonant cue (the F3 transition for [da] vs. [ga]) with the resonances of the remainder of the syllable. Perceiving duplexly, listeners hear the whistle of the sinusoid, but also the [da] and [ga] for which the sinusoid provides the critical information. In the first experiment, phonetic integration was significantly reduced, but not to zero, by a precursor that extended the transition cue forward in time so that it started 50 msec before the cue. The effect was the same above and below the duplexity threshold (the intensity of sinusoid in the combined pattern at which the whistle was just barely audible). In the second experiment, integration was reduced once again by the precursor, and also, but only below the duplexity threshold, by harmonics of the cues that were simultaneous with it. The third experiment showed that the simultaneous harmonics reduced phonetic integration only by serving as distractors while also permitting the conclusion that the precursor produced its effects by making the cue part of a coherent and competing auditory pattern, and so "capturing" it. The fourth experiment supported this interpretation by showing that for some subjects the amount of capture was reduced when the capturing tone was itself captured by being made part of a tonal complex. The results support the assumption that the independent phonetic system will integrate across disparate sources according to the cohesive power of that system as measured against the evidence for separate sources.