Effect of relative amplitude of frication on perception of place of articulation.

The amplitude of frication relative to vowel onset amplitude in the F3 and F5 formant frequency regions was manipulated for the synthetic fricative contrasts /s/-/integral of/ and /s/-/theta/, respectively. The influence of this relative amplitude manipulation on listeners' perception of place of articulation was tested by (1) varying the duration of frication from 30 to 140 ms, (2) pairing the frication noise with different vowels /i a u/, (3) placing formant transitions in conflict with relative amplitude, and (4) holding relative amplitude constant within a continuum while varying formant transitions and the amplitudes of spectral regions where relative amplitude was not manipulated. To determine if listeners were using absolute spectral cues or relative amplitude comparisons between frication and vowel for fricative identification, the frication and vowel were separated by (1) presenting the frication in isolation, and (2) inserting a gap of silence between the frication and vowel. The results showed that relative amplitude was perceived across vowel context and frication duration, and overrode context-dependent formant transition cues. The findings for temporal separations between the frication and vowel suggest that short-term memory processes may dominate the mediation of the relative-amplitude comparison. However, the overall results indicate that relative amplitude is only a component of spectral prominence, which is comprised of a primary frication spectral peak and a secondary frication/vowel peak comparison.