Individual differences in, and a comparison of, identification and similarity judgments of context-conditioned /S/ and /?/ phonemes

Abstract

Speech segments strongly influence the perception of adjacent speech segments. Such context effects provide interesting evidence of the interaction of acoustic information in the perceptual system. Studies that have dealt with such phenomena have focused on the effect of context on the label assigned to a phoneme, so that little is known about the within-class perception of context-conditioned phonemes. In the present study, the effect of vowel context on the perception of synthetic /s/- and /?/-like frication noises was examined in two experiments. A two-alternative forced-choice identification task confirmed that identification of the fricative in a set of consonant-vowel syllables was influenced by the vowel context. In a second experiment, the perceptual similarity of pairs of fricatives whose identity was influenced by the vowel was estimated in a triadic comparison task. INDSCAL analyses provided three dimensions that could account for 80.9% of the observed variance. However, individuals differed greatly on the contribution of each dimension to their similarity judgments. For some listeners, judgments of perceptual similarity were strongly related to their identification judgments. For other listeners, similarity of the fricatives was related to the physical differences between the fricatives, regardless of whether the fricatives had been identified as the same consonant or not. These results indicate that listeners differ in their abilities to perceive differences between phonemes that have been assigned the same label.