American English Diphthongs Research Articles

American English diphthong transitions and the acoustic vowel space: A pilot comparison of two tasks

The purpose of the present study is to evaluate the potential relationship(s) between diphthong transitions and the acoustic vowel space parameters in two speaking tasks. Diphthongs are associated with acoustic changes that reflect changes in vocal tract configurations, affording unique opportunities for investigating the articulatory-acoustic link. The acoustic vowel space, a representation of monophthong vowels in a two-dimensional plane defined by the first and second formant frequencies (F1 and F2), has been widely used to interpret articulatory-acoustic consequences and to index articulatory integrity. Nevertheless, limited is known as to how diphthongs and monophthong vowels account for the acoustic working space together [Lee et al., JASA 136(4), 1880–1894 (2014)]. To add to this inquiry, transitions of American English diphthongs /ei/, /ɑɪ/, /ɑʊ/, /oʊ/, and /ɔi/, defined by the primary F2 transition, are examined with respect to the quadrilateral vowel space anchored by /i/, /æ/, /ɑ/, and /u/. The speech sounds were obtained from four male speakers in two tasks, sentence reading and connected speech, that have been shown to elicit vowel space changes. It is hypothesized that greater diphthong transitions are associated with parameters corresponding to a larger vowel space. Findings will be discussed within the framework of the acoustic theory.

Intermittently tagged real-time MRI reveals internal tongue motion during speech production.

To demonstrate a tagging method compatible with RT-MRI for the study of speech production. Tagging is applied as a brief interruption to a continuous real-time spiral acquisition. Tagging can be initiated manually by the operator, cued to the speech stimulus, or be automatically applied with a fixed frequency. We use a standard 2D 1-3-3-1 binomial SPAtial Modulation of Magnetization (SPAMM) sequence with 1 cm spacing in both in-plane directions. Tag persistence in tongue muscle is simulated and validated in vivo. The ability to capture internal tongue deformations is tested during speech production of American English diphthongs in native speakers. We achieved an imaging window of 650-800 ms at 1.5T, with imaging signal to noise ratio ≥ 17 and tag contrast to noise ratio ≥ 5 in human tongue, providing 36 frames/s temporal resolution and 2 mm in-plane spatial resolution with real-time interactive acquisition and view-sharing reconstruction. The proposed method was able to capture tongue motion patterns and their relative timing with adequate spatiotemporal resolution during the production of American English diphthongs and consonants. Intermittent tagging during real-time MRI of speech production is able to reveal the internal deformations of the tongue. This capability will allow new investigations of valuable spatiotemporal information on the biomechanics of the lingual subsystems during speech without reliance on binning speech utterance repetition.

Creating a Pronunciation Profile of First‐Year Spanish Students

AbstractPrevious research has shown that improving pronunciation in the foreign language classroom is challenging, and there is often little time left over in a dense curriculum for pronunciation practice. In describing a pronunciation profile for all phonemes in Spanish, this study suggests that the principal challenge for native speakers of English who are learning Spanish may not be vowels, but the /r/ phonemes: the flap, the trill, and the cluster sound /tɾ/ pose the greatest challenges. Thus, if time is allocated to direct instruction in pronunciation, instructors and learners may focus on the pronunciation of Spanish language /r/ in its three forms, particularly since, when the /r/ phonemes are fronted in Spanish pronunciation, the following vowels are less likely to be pronounced as American English diphthongs. In addition, this study suggests that having students record themselves when reading aloud at multiple points during the course and then analyze and reflect on what they hear may result in pronunciation changes.

Developmental acoustic study of American English diphthongs.

Developmental trends of durational and spectral parameters of five American English diphthongs are investigated by age and gender. Specifically, diphthong durations, the fundamental frequency (F0), and the first three formant (F1, F2, F3) trajectories as well as formant transition rates are analyzed as a function of age, gender and diphthong type. In addition, the distance between diphthong onset and offset positions and those of nearby monophthongs in the formant space is computed and age-dependent trends are presented. Furthermore, a spectral transition mid-point is estimated for a given diphthong trajectory and normalized time durations from onsets to mid-points are analyzed as a function of age and diphthong type. Finally, diphthong classification results using formant-related parameters are reported. Results show the expected age-dependent reductions of diphthong duration, fundamental frequency, onset and offset formant values, and formant transition rate. More interestingly, it is evident that speakers adjust onset and offset positions of diphthongs with respect to monophthongs as a function of age. Normalized duration of the first demisyllable segment is found to be different among diphthongs and that younger children spend more time in the first segment. The implications for diphthong development and the onset-offset definition of diphthongs are discussed in detail.

Developmental aspects of American English diphthong trajectories in the formant space

Formant trajectories of five American English diphthongs embedded in the target words BAIT (/EY/), BITE (/AY/), POUT (/AW/), BOAT (/OU/), BOYS (/OY/) are investigated in the first two formant space as a function of age and gender. Age range considered is from 5 to 18 years. In this report, the focus is given on the differences in position between the start/end points of diphthongs and nine monophthongs. Averaged formant data across subjects in each age group are examined for this purpose. Two findings are worth mentioning. First, across all age groups, the start and end positions of diphthongs hardly match with the monophthongs that are typically used to transcribe the diphthongs across all age groups [cf. Holbrook and Fairbanks (1962)]. For instance, the start position of /EY/ is closer to /I/ than to /e/, and the end points of /EY, AY, OY/ are significantly different with respect to each other. Second, in addition to the larger size of vowel space, an overshoot trend toward the nominal end points of diphthongs is the most prominent developmental trend. That is, formant values of diphthongs produced by younger age children are closer to the nominal monophthongs used to transcribe the diphthongs.

An acoustical study of American English diphthongs.

English diphthongs are usually produced with more than one vocal tract shape. This study attempts to collect acoustical data of English diphthongs published by Hillenbrand et al. (1995) online and to examine acoustic features of the diphthongs for phoneticians and English teachers. 63 American males and females were chosen after excluding those subjects with different target vowels or ambiguous formant tracks. The author used PRAAT to obtain the acoustical data systematically at 11 equidistant timepoints over the diphthongal segment. Results show that the formant trajectories of the diphthongs produced by the American males and females appeared quite similar. When the female formant values were uniformly normalized to those of the males, almost a perfect collapse occurred. Second, the diphthongal movements on the vowel space appeared not linear due to the coarticulatory gesture for the following consonant. Third, the average duration of the diphthongs produced by the females was 1.156 times longer than that of the males while the pitch ratio between the two groups turned out to be 1.746 with a similar contour over measurement points. The author concludes that English diphthongs produced by various groups can be compared systematically when the acoustical values are obtained at proportional timepoints.

A study of articulatory kinematics of American English diphthongs.

Diphthongs are acoustically characterized by formant movements between initial and final vocalic segments [cf, Holbook and Fairbanks, J. Speech Hear. Res., (1962); Thomas Gay, J. Acoust. Soc. Am., (1968)]. It has been observed that the initial (onset) and final (offset) portions may not correspond to typical monophthongal vowels and that there exists more acoustic variability in the offset portions than in the onset portions. Spectral transition rates have been found to be different from diphthong to diphthong. In the current study, the articulatory properties of American English diphthongs are investigated in tandem with their acoustic properties. We collected both acoustic and articulatory data of five diphthongs and seven monophthongs in [b-t] context embedded in a carrier sentence using electromagnetic articulography. The data were recorded from two male and one female subjects, and each diphthong was repeated five times. The main analysis focus is on the kinematic characteristics of the three different tongue sensors (tongue tip, tongue dorsum, and tongue rear) in each diphthong production and the comparisons to monophthongs that are close to either the onset portion or the offset portion of the given diphthong. [Work supported by NIH.]

Quality of back vowels before /r/ in the American Inland North

Three American English diphthongs involving onsets in the back of the vowel space were investigated by means of acoustic measurements, discriminant analysis, and perceptual experiments. These diphthongs, termed DOOR/WAR, TOY, and STAR, were observed in the speech of ten young women residing in southern Michigan. The diphthongs were elicited in a variety of /b/-, /ɡ/-, and /h/-initial words (e.g. board, Boyd, and barred). Words with similar consonantal margins but different nuclei (e.g. bode, baud, and bod) were elicited, as well. The DOOR/WAR and TOY words were compared with bode and baud (and similar words with initial /ɡ/ and /h/), while the STAR words were compared with baud and bod (and similar words with initial /ɡ/ and /h/). All three methods of investigation showed that the initial part of the DOOR/WAR and TOY diphthongs more closely resembles that of bode than baud. On the other hand, the initial part of the STAR diphthong was shown to be intermediate between that of baud and that of bod.

Three approaches to the classification of American English diphthongs

Various investigations of diphthongs suggest that they can be effectively classified in terms of (1) the pattern of fundamental frequency and formants at the onset and offset of the production, (2) the onset formant pattern and the F 2 rate of transition or (3) the onset formant pattern and the direction of formant movement in an acoustic space. These three hypotheses were assessed in (a) a log F 1 × log F 2 space and (b) an “auditory–perceptual space” in which the dimensions are based on ratios between pairs of formants and between F 1 and a reference value related to the vowel’s average formant frequency. Values for relevant parameters were obtained for a corpus of 768 tokens of six American English diphthongs produced in two contexts ([b_d], [h_d]) at two tempos (slow, fast) with differing stress (stressed, unstressed). The hypotheses were evaluated in respect to classification performance using a statistical pattern recognition procedure. All three hypotheses produced correct classification of the corpus exceeding 90%, although highest correct classification was obtained by specification of onset and offset formant patterns (an average of 96%). Slightly higher percent correct classifications were obtained for each hypothesis when parameters are specified in the auditory–perceptual space rather than in the log F 1 × log F 2 space.

Acoustic correlates of American English diphthongs.

Various studies on diphthongs suggest that they can be effectively classified in terms of either (1) the pattern of the fundamental frequency and formants at the onset and offset of the production, (2) the onset pattern and the F2 rate of transition, or (3) the onset pattern and the direction of formant movement in an acoustic space [Nearey and Assmann, J. Acoust. Soc. Am. 80, 1297–1308 (1986)]. Extending earlier reports [Gottfried, J. Acoust. Soc. Am. 89, 1997 (1991)] these three hypotheses were assessed in (a) a log F1×log F2 space and (b) an auditory-perceptual space. Values for the relevant parameters were obtained for a corpus of 768 productions of American English diphthongs (6 diphthongs ×4 speakers ×2 tempos ×2 stress conditions ×2 consonantal contexts). The hypotheses were then evaluated in terms of classification performance using a statistical pattern recognition procedure. Results indicate that the acoustic parameters specified in each hypothesis were effective in obtaining correct classification of diphthongs. [Work was supported by NIDCD.]

An approach to the classification of American English diphthongs

Six diphthongs of American English (/au, aɪ, eɪ, oᴜ, ɔɪ, ju/) were produced by four midwestern American speakers (two male, two female) at two tempos (slow, fast) with differing stress (stressed, unstressed) in two contexts ([b_d], [h_d]). Using a plot of the fundamental frequency and the first three formants derived from linear‐prediction‐coding (LPC) analysis, the onset and offset of each production was determined. The pattern of formants and fundamental frequency at the onset and offset of diphthongs was used to establish a set of parameters that can classify intended productions of the American English diphthongs in varying stress and tempo conditions with an average accuracy of 93%. Results are also presented for diphthong, target‐syllable, and sentence durations. The classification results are discussed with respect to hypotheses concerning the perception of diphthongs.

Rate‐dependent variability in English and Japanese complex vowel F2 transitions

Are the effects of changes in speech rate on F2 transition slopes in languages with and without unitary diphthongs explicable in terms of general phonetic and physiological principles? Five American English diphthongs and four Japanese vowel sequences were recorded, spoken at three different tempos by eight and seven speakers, respectively. LPC spectra were computed at 10‐ms intervals, and the resulting F2 contours were analyzed by a computer program designed to objectively define and measure steady‐state and transitional portions of the vowel. Contrary to the claims of Gay [J. Acoust. Soc. Am. 44, 1570–1573 (1968)], speech rate was found to significantly affect two measures of transition slope in English, with slope decreasing as speech rate increased. Individual diphthong populations in both languages displayed high correlations between a transition, slope and its F2 range, indicating that rate adjustment is not simply a matter of target undershoot at faster speeds. Japanese showed less rate‐dependent variability, suggesting that temporal reorganization for different speech rates is affected by language‐specific structures. [Work supported by NIH.]

The effects of varying glide durations on diphthong identification.

Traditionally, diphthongs have been described as consisting of an initial steady-state portion, a glide, and a relatively short final steady-state portion. This study investigated the contribution of glides of variable duration, in the presence of steady-state portions of fixed duration, to diphthong identification. The three American English diphthongs /ai/, /au/ and /??/ were synthesized, employing fixed durations for the steady-state portions and varying the duration of the glide from zero (no glide) to approximately 150 msec. Two-vowel sequences, identical to the steady-state portions of the diphthongs and separated by "gaps" of varying durations, were also synthesized. Four different fundamental-frequency values were employed in the synthesis. The stimuli were presented to subjects, who were asked to identify each item as one of the three diphthongs or one of the three possible two-vowel sequences. The glide durations at which identification of the stimuli changed from diphthong to vowel sequence were different for the three vocalic sequences tested; the identification pattern was also influenced by the fundamental-frequency values.

Identification of synthetic diphthongs with variable transition duration

Traditionally, diphthongs have been described as consisting of an initial steady state portion, a transition, and a relatively short final steady state portion. Gay [“A Perceptual Study of American English Diphthongs,” Lang. and Speech 13, 65–88 (1970)] found that the presence of a transition without steady state portions is sufficient for the identification of synthetic diphthongs. This study investigated the contribution of transitions of variable duration, in the presence of steady state portions, to diphthong identification. The three American English diphthongs /ai/, /au/, and /oi/ were synthesized, employing fixed durations for the steady state portions and varying the duration of the transition from 0 (no transition) to approximately 150 msec. Two‐vowel sequences, identical to the steady state portions of the diphthongs and separated by pauses of varying durations, were also synthesized. Comparable sets of synthetic diphthongs and two‐vowel sequences, synthesized at different fundamental frequencies, were presented to different groups of subjects; the subjects were required to identify each stimulus item as one of the three diphthongs or one of the three possible two‐vowel sequences. When the transitions were short or absent, subjects were consistent in identifying the stimuli as diphthongs. For some stimulus items, even relatively long pauses separating two steady state vowel segments were ineffective in shifting the identification to a vowel sequence.

Cinefluorographic Studies of Selected American English Diphthongs

The observations reported in this paper pertain to the articulatory movements—especially tongue movements—that are associated with the American English diphthongs /al/, /ɔI/, and /aU/. Flesh points on the lingual surface were simulated by attaching small radiopaque markers to the midline of the tongue body. Lateral-view cinefluorography was used to record the displacement patterns of these markers during the production of diphthongs in isolated words and short sentences. Data were collected for three speech samples, each of which was read by a different set of two speakers. Consideration of these data emphasizes the general problem of identifying invariant phonemic correlates at the articulatory level, with illustrations of the variability in (1) the initial and terminal vocal-tract configurations for a given diphthong, (2) the patterns of tongue-point movement for a given diphthong, and (3) the tongue-point velocities during a given diphthong. [Research supported in part by grants from NIH.]

A perceptual study of American English diphthongs.

This study utilized synthetic speech for describing the phonemic boundaries and the effects of formant course on the identification of / i, ai, au/. In the first experiment, synthesized formant transitions appropriate to classes of / i-ai/ and /au-o/ were presented to ten phonetically trained listeners for purposes of phoneme labelling. Results showed that preferred / i/ courses were from [ ] or [u] to [i, y, I], /ai/ courses from [a] to [I] and /au/ from [a] to [ ]. The purpose of the second experiment was to determine whether the phonetic identity of the targets or the absolute course of the second formant transition serves as the primary identifying cue. These features were separated along the time dimension by synthesizing diphthongs whose second formant frequency course remained fixed but whose durations varied. Results of the listening tests showed shifts in perception from simple vowel to diphthong occurring as a function of duration rather than frequency onset or offset positions. Further, in the case of / i-ai/, second formant rate of change serves as the primary distinguishing cue. The results suggest / i, ai, au/ are characterized by an invariant second formant rate of change, whose onset and offset values vary across changes in duration.