Introduction

1. Listener’s variation in phoneme category boundary as a source of sound change: a case of /u/-fronting KATAOKA, Reiko (kataoka@berkeley.edu)Department of Linguistics, University of California at Berkeley, 1203 Dwinelle Hall, Berkeley, California 94720-2650 Material and Procedure (cont.) Analysis (cont.) Introduction Results (cont.) • THEORY: Sound change by hypo-correction (Ohala 1981) “Correction” “Hypo-correction” • “Correction” = Compensation for coarticulation (C for C) • “Hypo-correction” = Failure to compensate misperception • Source of hypo-correction: • Failure to detect context • Lack of experience for contextual variations (child, foreigner) • Findings from later studies suggest that there may be another source of ‘seeming’ hypo-correction. That is variation in compensation. E.g. 1) Variable nasality judgment (Beddor and Krakow, 1999) 2) Age group difference in C for C (Harrington et al., 2008) • A listener may reconstruct a pronunciation that differs from what the speaker assumes when the speech signal is more heavily coarticulated than what the listener would compensate for. • Thus, it follows that individuals would vary in the vowel they assume when learning a new word with a heavily coarticulated vowel if they have different ranges of compensation. The present study starts from this idea. • By using Fronters and Backers as groups, two-tailedt-test examined the group differences for: • 1) Perception category boundary,defined as 50% point on the probit function, in Fast, Medium, and Slow conditions; and • 2) Repetition category boundary, defined at a minimum of the first derivative of the cubic polynomial function (Figure 3). • Context effect (C for C) on vowel repetition was tested by Repeated Measure ANOVA on F2 of repeated vowels. • Stimuli: 10 equal-step /bip/-/bup/ and /dit/-/dut/ continua 1) Create a 10-step /i/-/u/ continuum (Figure 1). • Variable: F3 2969 Hz ----------- 2319 Hz (Δ=0.18 Bark) F2 2372 Hz ----------- 1200 Hz (Δ=0.50 Bark) • Vowel duration: 80, 100, & 120 ms (Fast, Medium, Slow) • Amplitude ramped first and last 15 ms • F0 contour: 120 Hz at onset  90 Hz at offset • 2) Add natural onset and coda burst to create /bVp/ and /dVt/ stimuli. (CVC duration: 170, 190, & 210 ms) • Procedure for perception tasks (2AFC) • no precursor: Stimulus presented in isolation (CVC = 190 ms) • w/precursor: Presented after “I guess the word is _____” • Three different speech rate (Fast,Medium, Slow) • Task: two-alternative forced-choice (/dit/ or /dut/; /bip/ or /bup/) • Block: 4 blocks (4 conditions) x 2 sub-blocks (2 contexts) • Trials: 10 tokens x 4 repetition = 40 trials for each sub-block • Procedure for production tasks (Vowel Repetition) • Stimuli used in ‘no precursor’ condition above were presented. • Task: Listen to the stimulus and immediately repeat the VOWEL. • Block: 3 blocks (3 contexts: Alveolar,Bilabial,Vowel alone) • Trials: 10 tokens x 4 repetition = 40 trials for each context • Subjects: Speakers of Am-Engl. (n=30: 18F, 12M; 19-49 yrs old) • C for C in Vowel Repetition Tasks • When ambiguous stimuli (#5 and #6) were repeated, the vowel repeated after /dVt/ stimuli had lower F2 than the vowel repeated after /bVp/ stimuli, but the differences were not significant ([F=2.39 (1, 29); p= 0.13] for #5; [F=1.24 (1, 29); p=0.27] for #6) Figure 3. Illustration of category boundary determined from the cubic polynomial function. The data are F2 of repeated vowels from /dVt/ and /bVp/ stimuli from all subjects. Figure 5. Distribution of F2 of repeated vowels, from /dVt/ stimuli and /bVp/ stimuli. Summary & Discussion • SUMMARY • The hypothesis (H1) that category boundary difference between the groups of subjects remains across different conditions was generally supported. These results confirm the robustness of category boundary in the listener’s perceptual space and systematic individual variations in category boundaries. • The hypotheses that perceptual C for C brings about context-induced variation in vowel imitation (H2) and that group difference in perceptual boundary transfers to the same difference in repetition boundary (H3) were not supported; however, the observed trends were consistent with the hypotheses. These results seem to suggest that the hypotheses may hold in different experimental conditions. • IMPLICATIONS • Listeners vary in terms of the ‘compensation grammar’ or the range of acoustic variation that the listeners compensate for coarticulation in a given context. • Speakers are capable of repeating (thus also learning) vowels into gradient categories. • From these, the following scenario is proposed as another case of ‘hypo-correction’: • Speaker produces ‘dude’ [dyd], assuming /dud/ • Listener A (Fronter) – hear it as [dyd], learn CVC as /dud/ • Listener B (Backer) – hear it as [dyd], learn CVC as /dyd/* • * (phoneme≠ a unit of lexical contrast, but a learnable sound category) Results . • Fronters vs. Backers: Vowel Category Boundary • Significant group difference was observed in five out of six planned comparisons, showing robustness of the boundary. • Fronters vs. Backers: Repetition Boundary • For /bVp/ stimuli, Fronter’s category boundary for repeated vowels was closer to /i/-end than Backer’s boundary, but the difference was not significant. Category boundaries for repeated vowels were comparable between the two groups for /dVt/ stimuli. Figure 4. Distribution of 50% response boundary by Fronters and Backerson a /dVt/ and a /bVp/ continuum in three test conditions---Fast, Medium, Slow, and no precursor condition, from which two groups were formed. Objective and Hypotheses • OBJECTIVE: By using an /i/-/u/ continuum, the study investigated: • Systematic individual variations in the /i/-/u/ boundary in perception tasks. • Relationships among vowel perception, C for C, and vowel repetition. • HYPOTHESES: • H1: A group of listeners (‘Fronters’) whose /i/-/u/ boundary is closer to /i/-end than the other group (‘Backers’) in one condition exhibits the same difference in other conditions as well. • H2: When an ambiguous vowel is heard for a repetition task, the repeated vowel would have lower F2 when heard in alveolar context than in bilabial context due to C for C. • H3: When an ambiguous vowel is repeated, the vowel repeated by the Fronters would have lower F2 than the vowels repeated by the Backers. Analysis • From the mean of 50% /i/-/u/ boundaries (determined by probit analysis of the responses in the 2AFC tasks in ‘no precursor’ condition) of the /dVt/ and /bVp/ continua, the subjects were classified into the following two groups: • Fronters – category boundary < 4.5 • Backers – category boundary > 4.5 Figure 2. The/u/-response functions of all subjects. Each line shows a single subject’s mean response to Alveolar (dVt) and Bilabial (bVp) stimuli (8 responses per stimulus). (n=30). Figure 5. Distribution of repetition boundary by Fronters and Backerson a /dVt/ and a /bVp/ continuum. Bibliography Materials and Methods Beddor, Patrice S., and Rene A. Krakow. 1999. Perception of coarticulatory nasalization by speakers of English and Thai: Evidence for partial compensation. Journal of the Acoustical Society of America 106(5):2868-2887. Harrington, J., Kleber, F., and Reubold, U. (2008). “Compensation for coarticulation, /u/-fronting, and sound change in standard southern British: An acoustic and perceptual study,” J. Acoust. Soc. Am. 123, 2825-2835. Ohala, J. J. (1981). “The listener as a source of sound change,” in Papers from Parasession on Language and Behavior, edited by C. S. Masek, R. A. Hendrick, and M. F. Miller (Chicago Linguistic Society, Chicago), pp. 178-203. • Figure 1. Spectrograms of a 10-step /i/ - /u/ continuum. Formant frequency (Hz) for the vowels are: F1=375, F2 & F3= variable, F4 = 3500, and F5 = 4500.