Using Acoustic Measurement as an Estimate of Vowel Intelligibility PSLLT 2021 June 18-19 Mahdi Duris Background • Intelligibility measurements of L2 speech involve 2 factors: the speaker and the listener • Listener’s judgments of intelligibility by way of ratings • In English segmentals: vowels are the nucleus (Fogerty & Humes, 2012) • Furthermore, vowel height (F1) carries 80% of the energy in a vowel (Ladefoged & Johnson, 2015) • Estimating vowel intelligibility using acoustic phonetic measurements has been successfully done by Koffi (2021) for L2 intelligibility (12,000 tokens across 7 different L2s) • Acoustic thresholds that consider the Critical Band Theory (CBT), Just Noticeable Differences (JND) and Relative Functional Load (RFL) to posit the Acoustic Masking and Intelligibility (AMI) theory • AMI theory states that “ segments that are acoustically close may mask each other with only minimal risk to intelligibility, unless their relative functional loads indicate otherwise.” (p. 55) • Phoneticians can measure vowel intelligibility instrumentally ≠listener ratings • L1 phonological background of L2 speakers is taken into account Current Gap • Focus on native listener ratings for intelligibility = lack of L2 speaker independent learning • Most technology assisted tools designed to improve intelligibility do not give direct feedback to speakers in consideration of their L1 phonological background • Feedback by an ideal-IPA for the segment, coded with ARPABET. No threshold considerations or pedagogical solutions • Koffi’s AMI theory enables phoneticians to assess vowel intelligibility while considering the speakers L1 inventory of vowels and not requiring the judgements of native listeners. To demonstrate the use of acoustic measurements as an estimate of vowel intelligibility, 32 advanced L1 Arabic speakers of English provided the data to respond to the following: 1. What are the L2 vowel characteristics of the participants? • This considers their L1 vowel inventory and provides a clear picture of potential problematic vowels 2. How similar or different are these vowels compared with General American English vowels? • Some vowels may be less problematic than others when considering intelligibility 3. Do the differences in F1 interfere with intelligibility? Introduction Participants • 32 Saudi EFL adult teachers (23 females, 9 males) • Mean age: 33 years old (ranging from 19 years to 53 years old) Stimuli • Modified read speech from the George Mason Speech Accent Archive: Please call Stella… Data Analysis • Each vowel analyzed was manually extracted from 3 different words using PRAAT • 7392 tokens (11 vowels x 3 repetitions x 32 participants x 7 correlates) in total were measured with only F1 and F2 used for this study (2,112 tokens) Table 1 Vowel sound names from the read speech. Thresholds • CBT: 60 Hz (F1) is a robust criterion for distinguishing between perceptually similar vowels (Labov et al., 2013). • JND: If the distance between 2 vowels for F1 is ≤60 Hz = masking is likely. Complete masking occurs when the acoustic distance is £ 20 Hz (Koffi, 2021:75) • RFL: The higher the RFL = the greater the likelihood of unintelligibility. • Internal masking: how a speaker distinguishes between the frequencies of their own vowels • External masking: how a speaker distinguishes between the frequencies of their vowel compared to the vowels of another speaker (speaker vs listener) Table 2 Intelligibility Assessment Matrix (Koffi, 2021:75) Methodology L2 Vowel Characteristics for female participants Figure 2 Vowel characteristics of female participants (internal vs external masking) Table 3 Acoustic Masking and Intelligibility assessment for female participants Summary: For female participants, only one pair of vowels are problematic when considering internal masking ([ɪ] vs. [e]). For external masking, two pairs of vowels are problematic ([i] vs. [ɪ] and [ɪ] vs. [e]) L2 Vowel Characteristics for male participants Figure 3 Vowel c