Three experiments tested the hypothesis that vowels play a disproportionate role in hearing talker identity, while consonants are more important in perceiving word meaning. In each study, listeners heard 128 stimuli consisting of two different words. Stimuli were balanced for same/different meaning, same/different talker, and male/female talker. The first word in each was intact, while the second was either intact (Experiment 1), or had vowels ("Consonants-Only") or consonants wels-Only") replaced by silence (Experiments 2, 3). Different listeners performed a same/ different judgment of either talker identity (Talker) or word meaning (Meaning). Baseline testing in Experiment 1 showed above-chance performance in both, with greater accuracy for Meaning. In Experiment 2, Talker identity was more accurately judged from Vowels-Only stimuli, with modestly better overall Meaning performance with Consonants-Only stimuli. However, performance with vowel-initial Vowels-Only stimuli in particular was most accurate of all. Editing Vowels-Only stimuli further in Experiment 3 had no effect on Talker discrimination, while dramatically reducing accuracy in the Meaning condition, including both vowel-initial and consonant-initial Vowels-Only stimuli. Overall, results confirmed a priori predictions, but are largely inconsistent with recent tests of vowels and consonants in sentence comprehension. These discrepancies and possible implications for the evolutionary origins of speech are discussed.

It has been proposed that infant-directed speech (IDS) increases the discriminability of phonetic categories by exaggerating the acoustic differences between phonetic units (Kuhl et al., 1997, Science). However, reports show conflicting results on whether this principle holds for consonants. The current study measured English /p/ /b/ /t/ /d/ in both IDS and adult-directed speech (ADS) from connected speech in 27 mothers addressing their 11-month-old infants. Findings supported the exaggeration hypothesis. The mean VOT of /p/ was longer in IDS than ADS, and approached significance for /t/. The mean VOT difference between /p/ and /b/ was greater in IDS than in ADS. Similarly, when phonemes were grouped into voiceless and voiced categories, the difference between categories was significantly greater in IDS than ADS. We will discuss ways to measure AD-ID differences. [Work supported by NIH HD37954.]

No abstract

Perceptual experiments tested whether consonants and vowels differentially contribute to phonetic versus indexical cueing in speech. In 2 experiments, 62 total participants each heard 128 American–English word pairs recorded by 8 male and 8 female talkers. Half the pairs were synonyms, while half were nonsynonyms. Further, half the pairs were words from the same talker, and half from different, same-sex talkers. The first word heard was unaltered, while the second was edited by setting either all vowels (‘‘Consonants-Only’’) or all consonants (‘‘Vowels-Only’’) to silence. Each participant responded to half Consonants-Only and half Vowels-Only trials, always hearing the unaltered word once and the edited word twice. In experiment 1, participants judged whether the two words had the same or different meanings. Participants in experiment 2 indicated whether the word pairs were from the same or different talkers. Performance was measured as latencies and d values, and indicated significantly greater sensitivity to phonetic content when consonants rather than vowels were heard, but the converse when talker identity was judged. These outcomes suggest important functional differences in the roles played by consonants and vowels in normative speech.