Use of vocalic cues to consonant voicing and native language background: the influence of experimental design

For native speakers of English and several other languages, preceding vocalic duration and F1 offset frequency are two of the cues that convey the stop consonant voicing distinction in word-final position. For speakers learning English as a second language, there are indications that use of vocalic duration, but not F1 offset frequency, may be hindered by a lack of experience with phonemic (i.e., lexical) vowel length (the "phonemic vowel length account": Crowther & Mann, 1992). In this study, native speakers of Arabic, a language that includes a phonemic vowel length distinction, were tested for their use of vocalic duration and F1 offset in production and perception of the English consonant-vowel-consonant forms pod and pot. The phonemic vowel length hypothesis predicts that Arabic speakers should use vocalic duration extensively in production and perception. On the contrary, Experiment 1 revealed that, consistent with Flege and Port's (1981) findings, they produced only slightly (but significantly) longer vocalic segments in their pod tokens. It further indicated that their productions showed a significant variation in F1 offset as a function of final stop voicing. Perceptual sensitivity to vocalic duration and F1 offset as voicing cues was tested in two experiments. In Experiment 2, we employed a factorial combination of these two cues and a finely spaced vocalic duration continuum. Arabic speakers did not appear to be very sensitive to vocalic duration, but they were about as sensitive as native English speakers to F1 offset frequency. In Experiment 3, we employed a one-dimensional continuum of more widely spaced stimuli that varied only vocalic duration. Arabic speakers showed native-English-like sensitivity to vocalic duration. An explanation based on the perceptual anchor theory of context coding (Braida et al., 1984; Macmillan, 1987; Macmillan, Braida, & Goldberg, 1987) and phoneme perception theory (Schouten & Van Hessen, 1992) is offered to reconcile the apparently contradictory perceptual findings. The explanation does not attribute native-English-like voicing perception to the Arabic subjects. The findings in this study call for a modification of the phonemic vowel length hypothesis.