ASA 129th Meeting - Washington, DC - 1995 May 30 .. Jun 06
5pSC26. Psychophysical procedure and the perceptual magnet effect:
Comparisons of fixed and roving AX discrimination of /i/.
Patricia K. Kuhl
Dept. of Speech and Hear. Sci., WJ-10, Univ. of Washington, Seattle, WA
Recent experiments by Iverson and Kuhl [ 553--562 (1995)] have
demonstrated that the perception of /i/ is influenced by category goodness.
Listeners exhibit a perceptual magnet effect characterized by high sensitivity
to acoustic differences near poor exemplars of /i/ and low sensitivity near
excellent exemplars of /i/. The present study examines whether this effect is
influenced by psychophysical procedures. Listeners were asked to discriminate
pairs of stimuli from an /i/ to /e/ continuum, and the task was varied in two
ways: (1) Each block of trials had either one pair of tokens (fixed
discrimination) or pairs of tokens from the entire stimulus range (roving
discrimination), and (2) the acoustic difference between each pair of tokens
was either 30 or 60 mels. The results demonstrated that the peak in
discrimination at the /i/-/e/ boundary diminished with fixed discrimination
tasks and 30-mel differences between tokens, supporting previous findings
[Macmillan et al., 1262--1280 (1988)]. However, the magnitude of the
perceptual magnet effect seemed less influenced by these manipulations. The
results suggest that distortions of sensitivity at boundaries and within
phonetic categories may arise from different mental processes.