Changes In Formant Frequencies Research Articles

Effects of speaking rate on vowel formant trajectories

The effects of speaking rate and vowel context on formant frequencies have traditionally been assessed by analyzing the variation in some operationally defined ‘‘target’’ frequency value. The use of a single frequency value to describe the behavior of a formant has proven useful for distinguishing among vocalic nuclei and identifying ‘‘target undershoot’’ effects of speaking rate. We have, however, only limited understanding of the characteristic effects of speaking rate change on formant trajectories. In our work, analysis of more complete representations of the time-varying changes in formant frequencies throughout vocalic nuclei have revealed patterns of formant change across speaking rates that differ qualitatively and quantitatively between speakers. These data suggest speaker-specific strategies for accomplishing speaking rate change. We have also observed that the acoustic effects of rate change within speakers differ qualitatively and quantitatively between different ranges of the vowel duration continuum. Thus, the acoustic effects of small changes in speaking rate at speaking rate extremes are not comparable to quantitatively identical changes at habitual rates. Since changes in speaking rate are commonly thought to correspond with changes in the overlap of neighboring articulatory gestures, these findings are pertinent to modeling coarticulation. [Work supported by NIH DC 0149-10.]

Speech patterns of children and adults elicited via a picture-naming task: An acoustic study

This brief study presents some acoustic phonetic characteristics that reflect both the voice characteristics and motor speech behaviour of 20 pre-adolescent (6-, 8- and 10-year olds) boys and girls, and 9 adults in speech data that were elicited via a picture-naming task. The acoustic phonetic characteristics that were investigated included formant frequency values, coarticulation (or gestural overlap) and temporal patterns. Both voice characteristics and motor speech behaviour presented evidence of age and sex differences, and age by sex interactions. In addition there were significant correlations between formant frequencies and their associated formant frequency changes (or excursions). There was also evidence of individual differences in the patterns of maturation, which did not conform to chronological age. These data are presented and discussed with reference to the sexual dimorphism of the vocal apparatus, the development of vocal characteristics, and motor speech development and behaviour.

Perception of Vocal Tract Resonances by Whooping Cranes Grus americana

Although formants (vocal tract resonances) can often be observed in avian vocalizations, and several bird species have been shown to perceive formants in human speech sounds, no studies have examined formant perception in birds’ own species‐specific calls. We used playbacks of computer‐synthesized crane calls in a modified habituation—dishabituation paradigm to test for formant perception in whooping cranes (Grus americana). After habituating birds to recordings of natural contact calls, we played a synthesized replica of one of the habituating stimuli as a control to ensure that the synthesizer worked adequately; birds dishabituated in only one of 13 cases. Then, we played the same call with its formant frequencies shifted. The birds dishabituated to the formant‐shifted calls in 10 out of 12 playbacks. These data suggest that cranes perceive and attend to changes in formant frequencies in their own species‐specific vocalizations, and are consistent with the hypothesis that formants can provide acoustic cues to individuality and body size.

Articulatory kinematic and formant frequency changes across vocalic nuclei: Some preliminary analyses

There are few data relating changes in articulatory position to changes in vocalic formant frequencies. This kind of information is useful for speech-production theory in general and specifically in understanding the relationship in neurogenic speech disorders between movement effects and resulting speech-intelligibility deficits. The purpose of this study was therefore to assemble a fairly large kinematic/acoustic database on normal speakers, for a few words that have proven useful in our studies of the intelligibility deficit in dysarthria. Data were part of the x-ray microbeam database, and for the present study included the words ‘‘hail,’’ ‘‘shoot,’’ and ‘‘coat.’’ The position histories of four tongue pellets and two lip pellets as well as the time histories of the first and second formant frequencies were studied for 45 young adult speakers. The F2 transition extent (change in F2 across a defined time interval) was significantly correlated with some combination of the pellet time histories for each word, and the magnitude of the correlation showed clear gender effects. Results will be discussed in terms of the linkage between planar kinematic data and acoustic data in predicting speech-intelligibility deficits. [Work supported by NIH DC03723 and DC000820.]

Acoustical-perceptual correlates of "whisper pitch" in synthetically generated vowels.

The purpose of this investigation was to clarify acoustical-perceptual relationships in identification of "pitch" during whispered vowel production. The experimenters systematically varied selected acoustic features of synthetically generated "whispered" vowels to control which formant frequencies were shifted (F1, F2, or F1&F2), the direction of formant frequency shifts (up or down), and the magnitude of formant frequency shifts (20 Hz, 40 Hz, 60 Hz). Two sets of stimuli were produced to simulate the resonance characteristics of the vowel /a/: one set for male talkers and one for female talkers. Ninety-four pairs of synthesized vowel tokens were randomly presented to 17 listeners who judged if the "pitch" of the second member of the pair was the same, higher, or lower than the "pitch" of the first member. The results showed an inverse relationship between the magnitude of formant frequency changes presented to the judges and the number of perceptual mismatches in "whisper pitch." Also, fewer mismatches in the identification of whisper pitch occurred when both F1 and F2 were changed simultaneously than when either F1 or F2 was changed individually. No differences were found between the perceptual responses to "male" and "female" vowel simulations. The primary implication of this study is that whisper pitch is more influenced by simultaneous changes in F1 and F2 than by changes in only one of the formants.

Age-related changes in human vocal tract configurations and the effects on speakers' vowel formant frequencies: a pilot study

The study aims to: (i) make accurate measurements of age-related changes in female speakers' vocal tract configurations with acoustic reflection technique (ART); (ii) obtain acoustic information of vowel formant frequency changes as a function of aging; and (iii) test the hypothesis that there are age-related vocal tract dimensional changes and concomitant decreases in all the vowel formant frequencies as people age. Preliminary findings indicate that older female subjects tend to have a more expanded pharyngeal lumen, but not longer vocal tract length, than their younger cohorts, and formant frequencies would not unanimously decrease as a function of aging. The study highlights the importance of larger-scale measurements of age-related vocal tract configuration changes and the necessity of developing new acoustic models that will delineate all the concomitant formant frequency and other acoustic changes as people age.

How steady are vowel steady-states?

The duration of vowel steady-states (VSS) was examined acoustically in the speech production of 40 normal young adults. VSS was assessed according to formant frequency changes in sustained /i/ productions and consonant +/i/ + /d/(/Cid/) productions. The duration of the VSS was measured for the first and second formants (Fl and F2) by incorporating a fixed rate-of-change criterion. Results indicated no significant differences in VSS duration according to gender or vowel context. VSS duration based on Fl was significantly longer than F2 VSS duration. The duration of VSS was also found to be correlated to the overall vowel duration in /Cid/ contexts. Discussion focuses on the analysis and application of VSS in acoustic studies of normal and disordered speech production.

How steady are vowel steady-states?

The duration of vowel steady-states (VSS) was examined acoustically in the speech production of 40 normal young adults. VSS was assessed according to formant frequency changes in sustained /i/ productions and consonant +/i/ + /d/(/Cid/) productions. The duration of the VSS was measured for the first and second formants (Fl and F2) by incorporating a fixed rate-of-change criterion. Results indicated no significant differences in VSS duration according to gender or vowel context. VSS duration based on Fl was significantly longer than F2 VSS duration. The duration of VSS was also found to be correlated to the overall vowel duration in /Cid/ contexts. Discussion focuses on the analysis and application of VSS in acoustic studies of normal and disordered speech production.

Temporal relationships of the articulatory, acoustic, and perceptual effects of fricative–vowel coarticulation

Anticipatory coarticulation has been extensively studied as part of the general phenomenon of coarticulation. However, the temporal relationships of the articulatory, acoustic, and perceptual effects of this particular type of coarticulation have not received much attention. The purpose of this study was to systematically examine lip protrusion gestures, acoustic and perceptual effects in fricative–vowel contexts, and explore the temporal relationships among these three effects. The onset of lip protrusion and acoustic effects as obtained and compared by employing a minimal contrast technique. The results showed that the onset of lip protrusion was much more consistent in a relative timeframe than in an absolute timeframe, and it was much earlier than, but independent of, the onset of traceable changes in formant frequencies. A reliable effect of anticipatory coarticulation on perception was also observed and the onset of this perceptual effect occurs tens of milliseconds later than the onset of the acoustic effect.

Modeling formant frequency discrimination of female vowels

The present investigations were designed to establish the features of vowel spectra that mediate formant frequency discrimination. Thresholds for detecting frequency shifts in the first and second formants of two steady-state vowels were initially measured for conditions in which the amplitudes of all harmonics varied in accordance with a model of cascade formant synthesis. In this model, changes in formant frequency produce level variations in components adjacent to the altered formant as well as in harmonics spectrally remote from the shifted resonant frequency. Discrimination thresholds determined with the cascade synthesis procedure were then compared to difference limens (DLs) obtained when the number of harmonics exhibiting level changes was limited to the frequency region surrounding the altered formant. Results indicated that amplitude variations could be restricted to one to three components near the shifted formant before significant increases in formant frequency DLs were observed. In a second experiment, harmonics remote from the shifted formant were removed from the stimuli. In most cases, thresholds for these reduced-harmonic complexes were not significantly different from those obtained with full-spectrum vowels. Preliminary evaluation of an excitation-pattern model of formant frequency discrimination indicated that such a model can provide good accounts of the thresholds obtained in the present experiments once the salient regions of the vowel spectra have been identified. Implications of these findings for understanding the mechanism mediating vowel perception are discussed.

Neural representation and psychophysical discrimination of vowel formants.

Auditory-nerve fiber responses were modeled to estimate neural representations of frequency changes in the second formant (ΔF2) of the steady-state vowel /eh. Simulations were performed at vowel levels of 33–84 dB, both in quiet and in continuous noise at a constant 3-dB signal-to-noise ratio (S/N). Signal detection analysis of model outputs suggested that formant changes at higher stimulus levels and in background noise were better represented by rate responses of fibers with low spontaneous rates (SR). Psychophysical tests were then performed in cats to measure behavioral thresholds for the detection of formant frequency changes under stimulus conditions similar to those of the neural simulations. Behavioral ΔF2’s were obtained at vowel levels of 10–70 dB, in quiet and in continuous background noise at S/Ns of 3, 13, and 23 dB. ΔF2 decreased with increasing vowel level and increased with decreasing S/N. These trends in psychophysical performance paralleled changes in the quality of vowel representations, particularly those based on discharge rates of low SR auditory-nerve fibers. [Work supported by NIDCD Grant Nos. 5R01DC01388-04 and 2R01DC00109-22.]

Interaction between duration, context, and speaking style in English stressed vowels

Acoustic observations are reported for English front vowels embedded in a /w—l/ frame and carrying constant main stress. The vowels were produced by five speakers in clear and citation-form styles at varying durations but at a constant speaking rate. The acoustic analyses revealed (i) that formant patterns were systematically displaced in the direction of the frequencies of the consonants of the adjacent pseudosymmetrical context; (ii) that those displacements depended in a lawful manner on vowel duration; (iii) that this context and duration dependence was more limited for clear than for citation-form speech, and that the smaller formant shifts of clear speech tended to be achieved by increases in the rate of formant frequency change. The findings are compatible with a revised, and biomechanically motivated, version of the vowel undershoot model [Lindblom, J. Acoust. Soc. Am. 35, 1773–1781 (1963)] that derives formant patterns from numerical information on three variables: The ‘‘locus-target’’ distance, vowel duration, and rate of formant frequency change. The results further indicate that the ‘‘clear’’ samples were not merely louder, but involved a systematic, undershoot-compensating reorganization of the acoustic patterns.

Effect of levels of stimulus uncertainty and consonantal context on formant frequency discrimination.

Discrimination thresholds for the second formant of vowels in consonantal context were significantly larger than for vowels in isolation in a report by Mermelstein [J. Acoust. Soc. Am. 63, 572 (1978)]. These results were not upheld in a recent report to this society [Kewley-Port and Watson, J. Acoust. Soc. Am. 89, 1996 (A) (1991)] for testing under minimal stimulus uncertainty procedures. Moreover, Mermelstein’s thresholds were a factor of 5 larger than those reported by Kewley-Port and Watson. The present experiment examines the effects of testing under higher levels of stimulus uncertainty in conditions more similar to those of Mermelstein. For well-trained subjects, most thresholds for the eight CVC stimuli tested did not change when levels changed from minimal to medium uncertainty. Further studies, using testing conditions similar to those of Mermelstein, employed untrained subjects. Results indicated that some subjects rapidly improved their ability to discriminate changes in formant frequency during just 1 h of testing. The differential effects of consonantal context, training, and levels of stimulus uncertainty will be discussed. [Research supported by NIH and AFOSR.]

Effects of distorted auditory feedback on speech.

A research program for acoustically measuring changes in speech production will be described. Here, F0 and spectrographic measurements target acoustic correlates of consonant, vowel, and syllabic stress features in 45 phonemically balanced words. To date, 5 Nucleus-22 multichannel cochlear implant patients have participated (at least) prestimulation, immediately after stimulation, 3–6 months after stimulation, and 1-year after stimulation. Commonalities among patients include: a rapid increase and stabilization of F0 (in females) to normal values; immediate and continuing changes in vowel and syllable durations and in relative amounts of breathy noise and low-frequency energy, gradual changes in vowel formant frequencies with movement still observed at 1 year; and changes in consonant properties (such as F1 cutback for voiceless stops) emerging for the first time at 1 year. Results relate to (1) the potential role of critical periods in the effect of auditory feedback on speech habits, (2) the relative susceptibility of speech features to modification, and (3) the likely auditory parameters available from Nucleus-22 WSP III stimulation. [Work supported by NIDCD.]

Differential sensitivity to vowel continua in Old World monkeys (Macaca) and humans

Previous studies indicate that monkey pure tone frequency discrimination is quantitatively and qualitatively very different from that of humans: Monkey DLs at 1.0 and 2.0 kHz are up to 20 times larger than human DLs, and monkeys DLs increase as sensation level increases, in contrast to human DLs [Sinnott et al., J. Acoust. Soc. Am. 78, 1977-1985 (1985); Sinnott et al., J. Comp. Psychol. 101, 126-131 (1987)]. These results led to an hypothesis that monkey frequency discrimination is more dependent upon "rate" coding than is that of humans. The present study compared monkey and human DLs for formant frequency changes along three synthetic vowel continua /I-i/, /ae-epsilon/, and /a-v/. Here, monkey DLs for formants near 1.0 and 2.0 kHz (32-48 Hz) were only about two to three times larger than human DLs (11-21 Hz), and both monkeys and humans exhibited relatively similar, flat sensation level functions. Taken together, these data indicate that monkey and human frequency discrimination is more similar in the case of a complex vowel stimulus than in the case of a simple pure tone stimulus. Results are discussed in relation to "rate" versus "temporal" coding of tones and vowels in the auditory system.

Effects of experimental manipulations of auditory feedback upon vowels

The role of auditory feedback upon intermediate vowel production was explored by manipulating the amount and type of information provided by a Nucleus multichannel cochlear implant. Four experimental conditions ,were examined: (a) two types of control conditions, the implant turned on versus off, and (b) two experimental conditions that varied the channels being stimulated. Twenty repetitions of the vowels [ɪ], [ɛ], [i], [u] in an hVd context were acquired from four adventitiously deafened adults using multichannel implants. Two of the vowels, [ɪ] and [ɛ], were selected because of previous work indicating significant changes in formant frequencies when the implant was turned on versus off. The vowels [i] and [u] were included as controls since previous work indicated that their formant frequencies failed to change when the implant was turned off. Recordings were digitized at a 20‐kHz rate and analyzed using CSpeech. Fundamental frequency, formant frequencies, and duration measures were acquired for each token. Data were statistically treated using a repeated measures ANOVA. Preliminary data indicates that the intermediate vowels rely upon relevant auditory information more heavily for their production than the control, point vowels. [Work supported by NIDCD.]

Perceived modulation magnitudes of second‐formant, center‐frequency variations

Speech signals convey information via rapid changes in formant frequencies. Listeners can reliably judge the relative “modulation magnitude” of frequency modulations [e.g., H. Fastl, Hear. Res., 59–69 (1982)]. Listeners were asked if they could also judge modulation magnitude for center‐frequency‐modulated formants by presenting pairs of 500‐ms stimuli with centered, “notchlike” modulations drawn from synthetic continua with varying notch duration (30–300 ms) or depth (50–500 Hz). The first, reference, stimulus (either a low‐ or high‐modulation extreme of a continuum) was assigned a reference magnitude (1 for low‐modulation‐reference trial blocks; 10 for high‐). Listeners assigned a relative “modulation strength” (1 to 10) to the second stimulus. Judged magnitude appears as an uneven perceptual surface in the magnitude × depth × duration space: Highest modulation strengths are heard for deep‐long stimuli; deep‐short stimuli have slightly lower judged magnitudes; shallow‐long modulations are much weaker; shallow‐short modulations are the weakest. The possible relation between perceived modulation magnitude and judgments of articulatory‐phonetic differences will be discussed. [Work supported in part by NIH‐NINCDS and the Louisiana Lions Eye Foundation.]

Acoustic-phonetic characteristics of speech produced in noise and while wearing an oxygen mask.

The present study investigated changes in the prosodic and acoustic-phonetic features of isolated words by four male talkers speaking in quite and in pink noise at a level of 95 dB SPL. Speech samples were collected both with and without an oxygen mask. Changes in duration, fundamental frequency, total energy, and formant center frequency were analyzed. In addition to the expected changes of increased pitch and amplitude associated with speaking in noise without an oxygen mask, significant effects were found (particularly in the formant center frequencies) as a result of using the oxygen mask. When the oxygen mask was employed, no further significant changes were caused by adding noise to the speaking situation.

The role of rate of transition in place perception

Kewley‐Port, Pisoni, and Studdert‐Kennedy [“Perception of static and dynamic acoustic cues to place of articulation in initial stop consonants,” J. Acoust. Soc. Am. 73, 1779–1793 (1983)] showed that initial bilabial and alveolar stops can be reliably identified from information in the first 20 ms of the syllable, including the burst and the beginning of the transition. Identification of stops as velars required a longer stimulus, indicating that a slow change in formant frequencies is characteristic of this place of articulation. If rate of change of formant frequencies is a positive cue to the identification of velar stops, it would be predicted that varying rate of change would affect their identification. To test this prediction, synthetic stop‐vowel stimuli, derived from natural tokens, consisting of all combinations of [b,d,g] and the vowels [i,a], were edited to produce stimuli with four rates of formant transition: 100, 75, 50, and 25 ms. Listeners in this experiment identified place of articulation consistently regardless of rate of transition; specifically, there was no significant interaction between place and rate of transition. This would indicate that a slow formant transition is not necessary if a stop is to be identified as a velar. There was, however, a significant interaction between vowel and place of articulation, which implies that the magnitude, if not the rate, of the transition is a significant cue to place.

From acoustic tube to acoustic cues

The relation between sound propagation in the acoustic tube and formant-based acoustic cues for the phonetic dimension of place of articulation is illustrated. The model for sound propagation comes from Chiba and Kajiyama [The Vowel (Phonetic Society of Japan, Tokyo, 1941)]. The evidence for the acoustic cues comes from the experimental literature published after 1941. The following are emphasized: (1) constriction of tubes and changes in formant frequencies; (2) constriction of tubes and invariants in the changes in formant frequencies; and (3) complexities of the changes in formant frequencies and simplifying rules derived from perceptual tests. A tape of modeled speech sounds will be played.