Differential effects of speaker and vowel variability on fricative perception

Previous research has shown that listeners' identifications of synthetic fricative noises are influenced by both rounding on an adjacent vowel and by the sex of the speaker who produced the adjacent vowel. In each case, contextual information which indicates a longer vocal tract during the production of the fricative (vowel rounding, or male speaker) results in fewer "sh" responses to the items in an [s] to [integral of] continuum (i.e., listeners expect generally lower vocal tract resonances from longer vocal tracts). The experiments reported here indicate that these superficially similar perceptual effects interact differently with manipulations of presentation type (blocked vs. randomized) and the interstimulus interval. When tokens produced by different speakers were presented blocked by speaker, the perceptual effect of speaker differences was reduced, and the degree of reduction depended on interstimulus interval. However, neither of these manipulations had an impact on the perceptual effect of vowel rounding.