Compensation for coarticulation reflects gesture perception, not spectral contrast

Abstract

This article reports three experiments designed to explore the basis for speech perceivers' apparent compensations for coarticulation. In the first experiment, the stimuli were members of three /da/-to-/ga/ continua hybridized from natural speech. The monosyllables had originally been produced in disyllables /ada/ and /aga/ to make Continuum 1, /alda/ and /alga/ (Continuum 2), and /arda/ and /arga/ (Continuum 3). Members of the second and third continua were influenced by carryover coarticulation from the preceding /l/ or /r/ context. Listeners showed compensation for this carryover coarticulation in the absence of the precursor /al/ or /ar/ syllables. This rules out an account in which compensation for coarticulation reflects a spectral contrast effect exerted by a precursor syllable, as previously has been proposed by Lotto, Holt, and colleagues (e.g., Lotto, Kluender, & Holt, 1997; Lotto & Kluender, 1998). The second experiment showed an enhancing effect of the endpoint monosyllables in Experiment 1 on identifications of preceding natural hybrids along an /al/-to-/ar/ continuum. That is, coarticulatory /l/ and /r/ information in /da/ and /ga/ syllables led to increased judgments of /l/ and /r/, respectively, in the precursor /al/-to-/ar/ continuum members. This was opposite to the effect, in Experiment 3, of /da/ and /ga/ syllables on preceding tones synthesized to range in frequency from approximately the ending F3 of /ar/ to the ending F3 of /al/. The enhancing, not contrastive, effect in Experiment 2, juxtaposed to the contrastive effect in Experiment 3, further disconfirms the spectral contrast account of compensation for coarticulation. A review of the literature buttresses that conclusion and provides strong support for an account that invokes listeners' attention to information in speech for the occurrence of gestural overlap.