Adaptive control of vowel formant frequency: evidence from real-time formant manipulation

Auditory feedback during speech production is known to play a role in speech sound acquisition and is also important for the maintenance of accurate articulation. In two studies the first formant (F1) of monosyllabic consonant-vowel-consonant words (CVCs) was shifted electronically and fed back to the participant very quickly so that participants perceived the modified speech as their own productions. When feedback was shifted up (experiment 1 and 2) or down (experiment 1) participants compensated by producing F1 in the opposite frequency direction from baseline. The threshold size of manipulation that initiated a compensation in F1 was usually greater than 60 Hz. When normal feedback was returned, F1 did not return immediately to baseline but showed an exponential deadaptation pattern. Experiment 1 showed that this effect was not influenced by the direction of the F1 shift, with both raising and lowering of F1 exhibiting the same effects. Experiment 2 showed that manipulating the number of trials that F1 was held at the maximum shift in frequency (0, 15, 45 trials) did not influence the recovery from adaptation. There was a correlation between the lag-one autocorrelation of trial-to-trial changes in F1 in the baseline recordings and the magnitude of compensation. Some participants therefore appeared to more actively stabilize their productions from trial-to-trial. The results provide insight into the perceptual control of speech and the representations that govern sensorimotor coordination.     

Vowel recognition via cochlear implants and noise vocoders: effects of formant movement and duration

Previous work has demonstrated that normal-hearing individuals use fine-grained phonetic variation, such as formant movement and duration, when recognizing English vowels. The present study investigated whether these cues are used by adult postlingually deafened cochlear implant users, and normal-hearing individuals listening to noise-vocoder simulations of cochlear implant processing. In Experiment 1, subjects gave forced-choice identification judgments for recordings of vowels that were signal processed to remove formant movement and/or equate vowel duration. In Experiment 2, a goodness-optimization procedure was used to create perceptual vowel space maps (i.e., best exemplars within a vowel quadrilateral) that included F1, F2, formant movement, and duration. The results demonstrated that both cochlear implant users and normal-hearing individuals use formant movement and duration cues when recognizing English vowels. Moreover, both listener groups used these cues to the same extent, suggesting that postlingually deafened cochlear implant users have category representations for vowels that are similar to those of normal-hearing individuals.     

An investigation of the third formant of /a/ in prepubertal children

The third formant (F₃) of /a/ recorded from 209 healthy children (104 male and 105 female; ages 3 to 12 years) and 40 adults (20 men and 20 women) was studied by spectral analysis. Contrary to the traditional concept, the results of this study showed that there is significant difference in voice F₃ of /a/ between male and female children. This difference was found to begin to develop at the age of 3 years and became substantial by the age of 6 years. In this study, the value of F₃ obtained from female children at the age of 6 years was unexpectedly higher than that from the male children at the same age, which indicates that there is a difference in timbre in small children of both sexes.     

Learning English vowels with different first-language vowel systems: perception of formant targets, formant movement, and duration

This study examined whether individuals with a wide range of first-language vowel systems (Spanish, French, German, and Norwegian) differ fundamentally in the cues that they use when they learn the English vowel system (e.g., formant movement and duration). All subjects: (1) identified natural English vowels in quiet; (2) identified English vowels in noise that had been signal processed to flatten formant movement or equate duration; (3) perceptually mapped best exemplars for first- and second-language synthetic vowels in a five-dimensional vowel space that included formant movement and duration; and (4) rated how natural English vowels assimilated into their L1 vowel categories. The results demonstrated that individuals with larger and more complex first-language vowel systems (German and Norwegian) were more accurate at recognizing English vowels than were individuals with smaller first-language systems (Spanish and French). However, there were no fundamental differences in what these individuals learned. That is, all groups used formant movement and duration to recognize English vowels, and learned new aspects of the English vowel system rather than simply assimilating vowels into existing first-language categories. The results suggest that there is a surprising degree of uniformity in the ways that individuals with different language backgrounds perceive second language vowels.     

Acoustic cues to lexical segmentation: a study of resynthesized speech

It has been posited that the role of prosody in lexical segmentation is elevated when the speech signal is degraded or unreliable. Using predictions from Cutler and Norris' [J. Exp. Psychol. Hum. Percept. Perform. 14, 113-121 (1988)] metrical segmentation strategy hypothesis as a framework, this investigation examined how individual suprasegmental and segmental cues to syllabic stress contribute differentially to the recognition of strong and weak syllables for the purpose of lexical segmentation. Syllabic contrastivity was reduced in resynthesized phrases by systematically (i) flattening the fundamental frequency (F0) contours, (ii) equalizing vowel durations, (iii) weakening strong vowels, (iv) combining the two suprasegmental cues, i.e., F0 and duration, and (v) combining the manipulation of all cues. Results indicated that, despite similar decrements in overall intelligibility, F0 flattening and the weakening of strong vowels had a greater impact on lexical segmentation than did equalizing vowel duration. Both combined-cue conditions resulted in greater decrements in intelligibility, but with no additional negative impact on lexical segmentation. The results support the notion of F0 variation and vowel quality as primary conduits for stress-based segmentation and suggest that the effectiveness of stress-based segmentation with degraded speech must be investigated relative to the suprasegmental and segmental impoverishments occasioned by each particular degradation.     

Developmental study of vowel formant frequencies in an imitation task.

Imitations of ten synthesized vowels were recorded from 33 speakers including men, women, and children. The first three formant frequencies of the imitations were estimated from spectrograms and considered with respect to developmental patterns in vowel formant structure, uniform scale factors for vowel normalization, and formant variability. Strong linear effects were observed in the group data for imitations of most of the English vowels studied, and straight lines passing through the origin provided a satisfactory fit to linear F1--F2 plots of the English vowel data. Logarithmic transformations of the formant frequencies helped substantially to equalize the dispersion of the group data for different vowels, but formant scale factors were observed to vary somewhat with both formant number and vowel identity. Variability of formant frequency was least for F1 (s.d. of 60 Hz or less for English vowels of adult males) and about equal for F2 and F3 (s.d. of 100 Hz or less for English vowels of adult males).     

Vowel formant discrimination II: Effects of stimulus uncertainty, consonantal context, and training.

This study is one in a series that has examined factors contributing to vowel perception in everyday listening. Four experimental variables have been manipulated to examine systematical differences between optimal laboratory testing conditions and those characterizing everyday listening. These include length of phonetic context, level of stimulus uncertainty, linguistic meaning, and amount of subject training. The present study investigated the effects of stimulus uncertainty from minimal to high uncertainty in two phonetic contexts, /V/ or /bVd/, when listeners had either little or extensive training. Thresholds for discriminating a small change in a formant for synthetic female vowels /I,E,ae,a,inverted v,o/ were obtained using adaptive tracking procedures. Experiment I optimized extensive training for five listeners by beginning under minimal uncertainty (only one formant tested per block) and then increasing uncertainty from 8-to-16-to-22 formants per block. Effects of higher uncertainty were less than expected; performance only decreased by about 30%. Thresholds for CVCs were 25% poorer than for isolated vowels. A previous study using similar stimuli [Kewley-Port and Zheng. J. Acoust. Soc. Am. 106, 2945-2958 (1999)] determined that the ability to discriminate formants was degraded by longer phonetic context. A comparison of those results with the present ones indicates that longer phonetic context degrades formant frequency discrimination more than higher levels of stimulus uncertainty. In experiment 2, performance in the 22-formant condition was tracked over 1 h for 37 typical listeners without formal laboratory training. Performance for typical listeners was initially about 230% worse than for trained listeners. Individual listeners' performance ranged widely with some listeners occasionally achieving performance similar to that of the trained listeners in just one hour.     

Perceived pitch of whispered vowels-relationship with formant frequencies: A preliminary study

To clarify the role of formant frequency in the perception of pitch in whispering, we conducted a preliminary experiment to determine (1.) whether speakers change their pitch during whispering; (2.) whether listeners can perceive differences in pitch; and (3.) what the acoustical features are when speakers change their pitch. The listening test of whispered Japanese speech demonstrates that one can determine the perceived pitch of vowel /a/ as ordinary, high, or low. Acoustical analysis revealed that the perception of pitch corresponds to some formant frequencies. Further data with synthesized whispered voice are necessary to confirm the importance of the formant frequencies in detail for perceived pitch of whispered vowels.     

276-nm absorption band system of m-dichlorobenzene: Rotational band contour analysis

The 276-nm absorption band system (${}^1\text{B}{}_2\text{←}{}^1\text{A}{}_1$) of m-dichlorobenzene was photographed under high resolution. The electronic origin band (0, 0) and a band at (0 + 380) cm^?1 were subjected to rotational “band contour” analysis. As a result, it is found that the origin band has a type A band contour and that at (0 + 380) cm^?1 exhibits a type B band contour. The band contour analysis also yields an accurate determination of the excited state parameters, viz., A′ = 0.0911 ± 0.0003, B′ = 0.02852 ± 0.00005, and C′ = 0.02175 ± 0.00001 cm^?1. A model geometry for the molecule m-DCB in its first excited singlet state has been proposed.     

Perception of front vowels: the role of harmonics in the first formant region

Vowel matching and identification experiments were carried out to investigate the perceptual contribution of harmonics in the first formant region of synthetic front vowels. In the first experiment, listeners selected the best phonetic match from an F1 continuum, for reference stimuli in which a band of two to five adjacent harmonics of equal intensity replaced the F1 peak; F1 values of best matches were near the frequency of the highest frequency harmonic in the band. Attenuation of the highest harmonic in the band resulted in lower F1 matches. Attenuation of the lowest harmonic had no significant effects, except in the case of a 2-harmonic band, where higher F1 matches were selected. A second experiment investigated the shifts in matched F1 resulting from an intensity increment to either one of a pair of harmonics in the F1 region. These shifts were relatively invariant over different harmonic frequencies and proportional to the fundamental frequency. A third experiment used a vowel identification task to determine phoneme boundaries on an F1 continuum. These boundaries were not substantially altered when the stimuli comprised only the two most prominent harmonics in the F1 region, or these plus either the higher or lower frequency subset of the remaining F1 harmonics. The results are consistent with an estimation procedure for the F1 peak which assigns greatest weight to the two most prominent harmonics in the first formant region.     

Adaptive auditory feedback control of the production of formant trajectories in the Mandarin triphthong /iau/ and its pattern of generalization

In order to test whether auditory feedback is involved in the planning of complex articulatory gestures in time-varying phonemes, the current study examined native Mandarin speakers' responses to auditory perturbations of their auditory feedback of the trajectory of the first formant frequency during their production of the triphthong /iau/. On average, subjects adaptively adjusted their productions to partially compensate for the perturbations in auditory feedback. This result indicates that auditory feedback control of speech movements is not restricted to quasi-static gestures in monophthongs as found in previous studies, but also extends to time-varying gestures. To probe the internal structure of the mechanisms of auditory-motor transformations, the pattern of generalization of the adaptation learned on the triphthong /iau/ to other vowels with different temporal and spatial characteristics (produced only under masking noise) was tested. A broad but weak pattern of generalization was observed; the strength of the generalization diminished with increasing dissimilarity from /iau/. The details and implications of the pattern of generalization are examined and discussed in light of previous sensorimotor adaptation studies of both speech and limb motor control and a neurocomputational model of speech motor control.     

The role of stimulus cross-splicing in an event-related potentials study. Misleading formant transitions hinder automatic phonological processing

The mental organization of linguistic knowledge and its involvement in speech processing can be investigated using the mismatch negativity (MMN) component of the auditory event-related potential. A contradiction arises, however, between the technical need for strict control of acoustic stimulus properties and the quest for naturalness and acoustic variability of the stimuli. Here, two methods of preparing speech stimulus material were compared. Focussing on the automatic processing of a phonotactic restriction in German, two corresponding sets of various vowel-fricative syllables were used as stimuli. The former syllables were naturally spoken while the latter ones were created by means of cross-splicing. Phonetically, natural and spliced syllables differed with respect to the appropriateness of coarticulatory information about the forthcoming fricative within the vowels. Spliced syllables containing clearly misleading phonetic information were found to elicit larger N2 responses compared to their natural counterparts. Furthermore, MMN results found for the natural syllables could not be replicated with these spliced stimuli. These findings indicate that the automatic processing of the stimuli was considerably affected by the stimulus preparation method. Thus, in spite of its unquestioned benefits for MMN experiments, the splicing technique may lead to interference effects on the linguistic factors under investigation.     

Discrimination of formant transition onset frequency: psychoacoustic cues at short, moderate, and long durations

Two experiments determined the just noticeable difference (jnd) in onset frequency for speech formant transitions followed by a 1800-Hz steady state. Influences of transition duration (30, 45, 60, and 120 ms), transition-onset region (above or below 1800 Hz), and the rate of transition were examined. An overall improvement in discrimination with duration was observed suggesting better frequency resolution and, consequently, better use of pitch/timbre cues with longer transitions. In addition, falling transitions (with onsets above 1800 Hz) were better discriminated than rising, and changing onset to produce increments in transition rate-of-change in frequency yielded smaller jnd's than changing onset to produce decrements. The shortest transitions displayed additional rate-related effects. This last observation may be due to differences in the degree of dispersion of activity in the cochlea when high-rate transitions are effectively treated as non-time-varying, wideband events. The other results may reflect mechanisms that extract the temporal envelopes of signals: Envelope slope and magnitude differences are proposed to provide discriminative cues that supplement or supplant weaker spectrally based pitch/timbre cues for transitions in the short-to-moderate duration range. It is speculated that these cues may also support some speech perceptual decisions.     

Low-temperature absorption contour of the ν3 band of SF6

A band contour analysis is carried out for the ν₃ absorption in SF₆. Values of ΔB = ? (1.0 ? 1.5) × 10^?4cm^?1, ζ₃ = 0.701, and ν₀ = 948.2cm^?1 are found. Tentative assignments are given for the SF₆ rotational states which are pumped by the P(14) through P(22) lines of the CO₂ laser.     

Perturbation theory at large order: The choice of integration contour

I discuss two technical points in the method of Lipatov for extracting the large-order behavior of field theories. The first is an adjustment of the integration contour required to make the action bounded below. The second is a method for treating fluctuations in the coupling constant exactly.     

Infrared band contour analysis and molecular constants of SPF3 and NSF3

Infrared spectra of gaseous SPF₃ and NSF₃ have been recorded at various temperatures. The band contours of the E fundamentals were analyzed by computer simulation taking into account the dependence of the rotational constants on the vibrational state. The ζ values together with centrifugal distortion constants (only for SPF₃) and isotope shifts Δν_i(³²S/³⁴S) were used as additional data in force constant calculations. CNDO calculations have been carried out to distinguish between two sets of force constants for the E block of NSF₃. An interpretation of the calculated stretch-stretch interaction force constants, f_rR, is given. Anharmonicity constants X₄₆ for SPF₃ and NSF₃ were determined.     

Effect of multiple reemission on the shape of the magnetic depolarization contour. II

The equations for the reflection and transmission functions of polarized resonant radiation are solved for the case of a layer of small optical thickness in the presence of a magnetic field H. Results of numerical calculations are presented. It is found that even at small the rotation of the polarization plane exceeds 45, as shown by the appearance of a negative value of the Stokes parameter Q as H rises. Finally, the passage of radiation through an optically thick layer is considered, and it is established that with an increase in the width of the depolarization contour decreases indefinitely.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 12, pp. 30–35, December, 1976.The author thanks V. L. Ginzburg for a discussion of the work.     

Influence of spectral-dynamic effects in a laser and light guide on the dynamics of recirculation in a closed contour

The influence of stimulated emission delay, dynamic shift in generation frequency, residual charge effect, timing jitter of the radiation and excitation regime of an injection laser, as well as of dispersion in a fiber light guide on the data-internal storage time in an electrooptical contour is investigated. It is found that the storage duration of an interval depends strongly on the lifetime of nonequilibrium charge carriers, the simultaneous effect of a residual charge and jitter in an injection laser, as well as on the dc bias current of the laser. Belarusian State University, 4. F. Skorina Ave., Minsk, 220050, Belarus. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 65, No. 1, pp. 56–61, January–February, 1998.