Effects of stimulus naturalness and contralateral interferers on lexical bias in consonant identification

Abstract

Lexical bias is the tendency to perceive an ambiguous speech sound as a phoneme completing a word; more ambiguity typically causes greater reliance on lexical knowledge. A speech sound ambiguous between /g/ and /k/ is more likely to be perceived as /g/ before /ɪft/ and as /k/ before /ɪs/. The magnitude of this difference—the Ganong shift—increases when high cognitive load limits available processing resources. The effects of stimulus naturalness and informational masking on Ganong shifts and reaction times were explored. Tokens between /gɪ/ and /kɪ/ were generated using morphing software, from which two continua were created (“giss”–“kiss” and “gift”–“kift”). In experiment 1, Ganong shifts were considerably larger for sine- than noise-vocoded versions of these continua, presumably because the spectral sparsity and unnatural timbre of the former increased cognitive load. In experiment 2, noise-vocoded stimuli were presented alone or accompanied by contralateral interferers with constant within-band amplitude envelope, or within-band envelope variation that was the same or different across bands. The latter, with its implied spectro-temporal variation, was predicted to cause the greatest cognitive load. Reaction-time measures matched this prediction; Ganong shifts showed some evidence of greater lexical bias for frequency-varying interferers, but were influenced by context effects and diminished over time.