ASA 130th Meeting - St. Louis, MO - 1995 Nov 27 .. Dec 01

2aSC4. Categorization of stop consonants in /sCs/ context.

Michael Kiefte

Terrance M. Neary

Dept. of Ling., Univ. of Alberta, Edmonton, AB T6H 4N1, Canada

To study the effects of silence duration and frication frequency on the perception of stop consonants in /sCs/ context, a two-dimensional continuum of stimuli ranging through /f(inverted vee)s/, /f(inverted vee)sts/, /f(inverted vee)sps/ and /f(inverted vee)sks/ was synthesized. Silence inserted within the /s/ frication ranged from 0--120 ms in 13 steps of 10 ms, while the frication center frequency immediately surrounding the gap varied from 1500--4500 Hz in nine linearly spaced steps. Stimuli with a 0 ms gap had no change in overall amplitude near the insertion target, while stimuli in which frication frequency was held at 4500 Hz (that of /s/) had no change in spectral shape. Fifteen subjects were asked to categorize the stimuli as either fuss, fus-s, fusts, fusps or fusks. Subjects were told to respond with fus-s when a specific consonant was not perceived, even though two /s/ sounds could clearly be distinguished. Results from a logistic regression showed that both gap duration and the frication frequency immediately surrounding have a significant effect on categorizations of the three stop consonants (p<0.0005). However, the linearity constraint imposed by a standard logistic regression appears to be too strong. Two other possibilities---quadratic categorical boundaries and hierarchical decision processes---are discussed as alternatives. [Work supported by SSHRC.]