An adaptive procedure for estimating phoneme-boundaries: Application to selective adaptation for speech

Abstract

Previous studies have estimated the boundary between two phoneme categories from identification data. This procedure is time consuming, especially in studies of selective adaptation where it is necessary to test identification twice, before and during adaptation. We developed a simple up-down adaptive procedure to estimate the phoneme boundary. The stimulus to be presented on a given trial is determined from the Ss' past responses. Two stimulus continua were synthesized; A voicing continuum (13 stimuli changing from /ba/ to /pa/) and a place continuum (13 stimuli changing from /ba/ to /da/ and /ga/. Ss were given an identification test with each set of stimuli. A logistic curve was fit to the obtained identification function of each subject. Next, phoneme boundaries were directly estimated with the adaptive procedure. The 50% points on the curves from the identification procedure were highly correlated with the 50% points estimated by the adaptive procedure. Phoneme boundaries were also measured before and during selective adaptation (using all endpoint stimuli as adaptors in separate sessions). Boundary shifts were obtained in the expected directions and magnitudes. The adaptive procedure is fast and exhibits high test-retest reliability. [Work supported by NIH.]