This study compares phonetic implementation of the stop voicing contrast produced in Arabic by Saudi Arabians and by both Americans and Saudis in English. The English stops produced by Saudis manifested temporal acoustic correlates of stop voicing (VOT, stop closure duration, and vowel duration) similar to those found in Arabic stops. Despite such phonetic interference from Arabic to English, however, American listeners generally had little difficulty identifying the English stops produced by the Saudis, with the exception of /p/. This phoneme, which is absent in Arabic, was frequently produced with glottal pulsing during the stop closure interval. The timing of /p/, however, suggests that the Saudis did grasp the phonological nature of /p/ (i.e., that the contrast between /p—b/ is analogous to that between /t—d/ and /k—g/) but were unable to control all the articulatory dimensions by which this sound is produced.

The evidence for isochrony of stress timing is weak at best for ordinary prose, but this does not mean that the timing of stresses is always unaffected by global constraints. We asked subjects to continually repeat the phrase Take a pack of cards and to temporally align the words take and cards with an auditorily presented stimulus consisting of just the words take and cards repeated several times. The phase of the cards stimulus relative to a reference cycle defined by the take-take interval was varied over the range 0.3-0.65 in eight equal-sized phase steps. The distribution of actually produced phases for the vowel onset of the syllable cards, however, was strongly trimodal. Subjects showed a powerful preference for phases close to 0.5, and somewhat weaker preferences for phases near 0.36 and 0.6. These values are close to (although systematically different from) 0.33 and 0.66 predicted by a simple harmonic model for stress timing. The observed distribution had this form whether the subjects were speaking along with the stimulus, or trying to maintain the prescribed timing after cessation of the stimulus. Furthermore, the observed phase was influenced by the phase produced on previous trials, suggesting dynamic control with hysteresis between competing stable patterns of timing. These results demonstrate strong rhythmic constraints on the timing of stresses within a phrase, where the domain of 'phrase' in this artificial speaking task is simply the repeated text. The rhythmic constraints are similar to those observed for limb movements. Modeling these constraints should provide insight into the form of a general dynamic control regime for global speech timing, and may allow improved characterization of 'natural' timing patterns in English speech.

Several experiments investigate voicing judgments in minimal pairs like rabid-rapid when the duration of the first vowel and the medial stop are varied factorially and other cues for voicing remain ambiguous. In Experiments 1 and 2, in which synthetic labial and velar-stop voicing pairs are investigated, the perceptual boundary along a continuum of silent consonant durations varies in constant proportion to increases in the duration of the preceding vocalic interval.In Experiment 3, it is shown that speaking tempo external to the test word has far smaller effects on a closure duration boundary for voicing than does the tempo within the test word. Experiment 4 shows that, even within the word, it is primarily the preceding vowel that accounts for changes in the consonant duration effects. Furthermore, in Experiments 3 and 4, the effects of timing outside the vowel-consonant interval are independent of the duration of that interval itself. These findings suggest that consonant/vowel ratio serves as a primary acoustic cue for English voicing in syllable-final position and imply that this ratio possibly is directly extracted from the speech signal.Twenty-five years ago, Denes (1955) reported an interesting phenomenon regarding the perception of phonological voicing by English listeners. He found that a voiceless final fricative in a synthetically constructed monosyllable could be heard as having either the plus or minus value of the English voicing feature, depending on the relative duration of the vowel and final fricative itself for words like his and hiss.

Chomsky and Halle (1968) and many formal linguists rely on the notion of a universally available phonetic space defined in discrete time. This assumption plays a central role in phonological theory. Discreteness at the phonetic level guarantees the discreteness of all other levels of language. But decades of phonetics research demonstrate that there exists no universal inventory of phonetic objects. We discuss three kinds of evidence: first, phonologies differ incommensurably. Second, some phonetic characteristics of languages depend on intrinsically temporal patterns, and, third, some linguistic sound categories within a language are different from each other despite a high degree of overlap that precludes distinctness. Linguistics has mistakenly presumed that speech can always be spelled with letter-like tokens. A variety of implications of these conclusions for research in phonology are discussed.*

This study attempts to determine the ways in which linguistic timing factors combine with each other in the production of English and specifically, to test and explore aspects of the timing model of Klatt [J. Acoust. Soc. Am. 59, 1208-1221 (1976)]. In two experiments the tensity feature of a sentence stressed vowel and the voicing of the following stop were changed along with a variable that alters the length of the VB syllable. The duration of both the vowel, V, and the following stop closure, C were measured. In the first experiment either one or two unstressed syllables are added to the word and in the second speaking tempo is changed. The significant results of both experiments are accounted for with a formal timing model that separately specifies (1) the Vm + C duration (where Vm = mean duration across the two vowels /i/ and /I/) depending on tempo or word length, (2) the ratio Vm/C depending on the voicing of the stop (/b/ or /p/), and (3) as a final ordered step, a rule that adjusts the vowel length by a constant ratio depending on the identity of the vowel. This integrated model provides for (1) the "incompressiblity" effects, (2) prosodic properties, and (3) the constant V/C ratios for values of the voicing feature found in perception experiments.