Formant Frequency Discrimination Research Articles

Auditory Models for Formant Frequency Discrimination of Vowel Sounds

As formant frequencies of vowel sounds are critical acoustic cues for vowel perception, human listeners need to be sensitive to formant frequency change. Numerous studies have found that formant frequency discrimination is affected by many factors like formant frequency, speech level, and fundamental frequency. Theoretically, to perceive a formant frequency change, human listeners with normal hearing may need a relatively constant change in the excitation and loudness pattern, and this internal change in auditory processing is independent of vowel category. Thus, the present study examined whether such metrics could explain the effects of formant frequency and speech level on formant frequency discrimination thresholds. Moreover, a simulation model based on the auditory excitation-pattern and loudness-pattern models was developed to simulate the auditory processing of vowel signals and predict thresholds of vowel formant discrimination. The results showed that predicted thresholds based on auditory metrics incorporating auditory excitation or loudness patterns near the target formant showed high correlations and low root-mean-square errors with human behavioral thresholds in terms of the effects of formant frequency and speech level). In addition, the simulation model, which particularly simulates the spectral processing of acoustic signals in the human auditory system, may be used to evaluate the auditory perception of speech signals for listeners with hearing impairments and/or different language backgrounds.

Effects of sensorineural hearing loss on formant-frequency discrimination: Measurements and models

This study concerns the effect of hearing loss on discrimination of formant frequencies in vowels. In the response of the healthy ear to a harmonic sound, auditory-nerve (AN) rate functions fluctuate at the fundamental frequency, F0. Responses of inner-hair-cells (IHCs) tuned near spectral peaks are captured (or dominated) by a single harmonic, resulting in lower fluctuation depths than responses of IHCs tuned between spectral peaks. Therefore, the depth of neural fluctuations (NFs) varies along the tonotopic axis and encodes spectral peaks, including formant frequencies of vowels. This NF code is robust across a wide range of sound levels and in background noise. The NF profile is converted into a rate-place representation in the auditory midbrain, wherein neurons are sensitive to low-frequency fluctuations. The NF code is vulnerable to sensorineural hearing loss (SNHL) because capture depends upon saturation of IHCs, and thus the interaction of cochlear gain with IHC transduction. In this study, formant-frequency discrimination limens (DLFFs) were estimated for listeners with normal hearing or mild to moderate SNHL. The F0 was fixed at 100 Hz, and formant peaks were either aligned with harmonic frequencies or placed between harmonics. Formant peak frequencies were 600 and 2000 Hz, in the range of first and second formants of several vowels. The difficulty of the task was varied by changing formant bandwidth to modulate the contrast in the NF profile. Results were compared to predictions from model auditory-nerve and inferior colliculus (IC) neurons, with listeners’ audiograms used to individualize the AN model. Correlations between DLFFs, audiometric thresholds near the formant frequencies, age, and scores on the Quick speech-in-noise test are reported. SNHL had a strong effect on DLFF for the second formant frequency (F2), but relatively small effect on DLFF for the first formant (F1). The IC model appropriately predicted substantial threshold elevations for changes in F2 as a function of SNHL and little effect of SNHL on thresholds for changes in F1.

Formant-frequency discrimination in listeners with hearing loss: Behavioral results and neural models

In responses of the healthy ear to harmonic sounds, the amplitude of f0-related fluctuations of auditory-nerve (AN) responses varies along the tonotopic axis. Neural fluctuation amplitudes encode spectral peaks, including formant frequencies of vowels, because responses of inner-hair-cells (IHCs) tuned near spectral peaks are captured (or dominated) by a single harmonic, resulting in lower fluctuation amplitudes than IHCs tuned between spectral peaks. This code is robust across a wide range of sound levels and in background noise, and is converted into a rate-place representation in the auditory midbrain, where neurons are sensitive to low-frequency fluctuations. This neural-fluctuation code is vulnerable to sensorineural hearing loss (SNHL), because it depends upon saturation of IHCs and the interaction of cochlear amplification with IHC transduction. We tested formant-frequency discrimination in listeners with normal hearing or mild to moderate SNHL. The difficulty of the task was modulated by varying formant bandwidth. The relationship between spectral peaks and harmonic frequencies was also varied. Formant frequencies were 600 and 2000 Hz, in the range of first and second formants of many vowels. Results were compared to predictions made using model AN and midbrain neurons, with audiograms for the individual listeners included in the peripheral model. [Work supported by NIDCD-R01-001641]

Formant frequency discrimination with a fine structure sound coding strategy for cochlear implants

Recent sound coding strategies for cochlear implants (CI) have focused on the transmission of temporal fine structure to the CI recipient. To date, knowledge about the effects of fine structure coding in electrical hearing is poorly charactarized.The aim of this study was to examine whether the presence of temporal fine structure coding affects how the CI recipient perceives sound. This was done by comparing two sound coding strategies with different temporal fine structure coverage in a longitudinal cross-over setting. The more recent FS4 coding strategy provides fine structure coding on typically four apical stimulation channels compared to FSP with usually one or two fine structure channels.34 adult CI patients with a minimum CI experience of one year were included. All subjects were fitted according to clinical routine and used both coding strategies for three months in a randomized sequence. Formant frequency discrimination thresholds (FFDT) were measured to assess the ability to resolve timbre information. Further outcome measures included a monosyllables test in quiet and the speech reception threshold of an adaptive matrix sentence test in noise (Oldenburger sentence test). In addition, the subjective sound quality was assessed using visual analogue scales and a sound quality questionnaire after each three months period.The extended fine structure range of FS4 yields FFDT similar to FSP for formants occurring in the frequency range only covered by FS4. There is a significant interaction (p = 0.048) between the extent of fine structure coverage in FSP and the improvement in FFDT in favour of FS4 for these stimuli. FS4 Speech perception in noise and quiet was similar with both coding strategies. Sound quality was rated heterogeneously showing that both strategies represent valuable options for CI fitting to allow for best possible individual optimization.

Development of an Acoustic Simulation Method during Phonation of the Japanese Vowel /a/ by the Boundary Element Method

The purpose of the present study was to establish the method for an acoustic simulation of a vocal tract created from CT data during phonation of the Japanese vowel /a/ and to verify the validity of the simulation. The subjects were 15 healthy adults (8 males, 7 females). The vocal tract model was created from CT data acquired during sustained phonation of the Japanese vowel /a/. After conversion to a mesh model for analysis, a wave acoustic analysis was performed with a boundary element method. The wall and the bottom of the vocal tract model were regarded as a rigid wall and a nonrigid wall, respectively. The acoustic medium was set to 37°C, and a point sound source was set in the place corresponding to the vocal cord as a sound source. The first and second formant frequencies (F1 and F2) were calculated. For 1 of the 15 subjects, the range from the upper end of the frontal sinus to the tracheal bifurcation was scanned, and 2 models were created: model 1 included the range from the frontal sinus to the tracheal bifurcation; and model 2 included the range from the frontal sinus to the glottis and added a virtually extended trachea by 12 cm cylindrically. F1 and F2 calculated from models 1 and 2 were compared. To evaluate the validity of the present simulation, F1 and F2 calculated from the simulation were compared with those of the actual voice and the sound generated using a solid model and a whistle-type artificial larynx. To judge the validity, the vowel formant frequency discrimination threshold reported in the past was used as a criterion. Namely, the relative discrimination thresholds (%), dividing ▵F by F, where F was the formant frequency calculated from the simulation, and ▵F was the difference between F and the formant frequency of the actual voice and the sound generated using the solid model and artificial larynx, were obtained. F1 and F2 calculated from models 1 and 2 were similar. Therefore, to reduce the exposure dose, the remaining 14 subjects were scanned from the upper end of the frontal sinus to the glottis, and model 2 with the trachea extended by 12 cm virtually was used for the simulation. The averages of the relative discrimination thresholds against F1 and F2 calculated from the actual voice were 5.9% and 4.6%, respectively. The averages of the relative discrimination thresholds against F1 and F2 calculated from the sound generated by using the solid model and the artificial larynx were 4.1% and 3.7%, respectively. The Japanese vowel /a/ could be simulated with high validity for the vocal tract models created from the CT data during phonation of /a/ using the boundary element method.

Midbrain Synchrony to Envelope Structure Supports Behavioral Sensitivity to Single-Formant Vowel-Like Sounds in Noise.

Vowels make a strong contribution to speech perception under natural conditions. Vowels are encoded in the auditory nerve primarily through neural synchrony to temporal fine structure and to envelope fluctuations rather than through average discharge rate. Neural synchrony is thought to contribute less to vowel coding in central auditory nuclei, consistent with more limited synchronization to fine structure and the emergence of average-rate coding of envelope fluctuations. However, this hypothesis is largely unexplored, especially in background noise. The present study examined coding mechanisms at the level of the midbrain that support behavioral sensitivity to simple vowel-like sounds using neurophysiological recordings and matched behavioral experiments in the budgerigar. Stimuli were harmonic tone complexes with energy concentrated at one spectral peak, or formant frequency, presented in quiet and in noise. Behavioral thresholds for formant-frequency discrimination decreased with increasing amplitude of stimulus envelope fluctuations, increased in noise, and were similar between budgerigars and humans. Multiunit recordings in awake birds showed that the midbrain encodes vowel-like sounds both through response synchrony to envelope structure and through average rate. Whereas neural discrimination thresholds based on either coding scheme were sufficient to support behavioral thresholds in quiet, only synchrony-based neural thresholds could account for behavioral thresholds in background noise. These results reveal an incomplete transformation to average-rate coding of vowel-like sounds in the midbrain. Model simulations suggest that this transformation emerges due to modulation tuning, which is shared between birds and mammals. Furthermore, the results underscore the behavioral relevance of envelope synchrony in the midbrain for detection of small differences in vowel formant frequency under real-world listening conditions.

Overlapping frequency coverage and simulated spatial cue effects on bimodal (electrical and acoustical) sentence recognition in noise

Sentence recognition in 20-talker babble was measured in eight Nucleus cochlear implant (CI) users with contralateral residual acoustic hearing. Speech reception thresholds (SRTs) were measured both in standard configurations, with some frequency regions presented both acoustically and electrically, and in configurations with no spectral overlap. In both cases a continuous interleaved sampling strategy was used. Mean SRTs were around 3 dB better with bimodal presentation than with CI alone in overlap configurations. A spherical head model was used to simulate azimuthal separation of speech and noise and provided no evidence of a contribution of spatial cues to bimodal benefit. There was no effect on bimodal performance of whether spectral overlap was present or was eliminated by switching off electrodes assigned to frequencies below the upper limit of acoustic hearing. In a subsequent experiment the CI was acutely re-mapped so that all available electrodes were used to cover frequencies not presented acoustically. This gave increased spectral resolution via the CI as assessed by formant frequency discrimination, but no improvement in bimodal performance compared to the configuration with overlap.

The effect of perimodiolar placement on speech perception and frequency discrimination by cochlear implant users

Conclusion. Neither speech understanding nor frequency discrimination ability was better in Nucleus Contour™ users than in Nucleus 24 straight electrode users. Furthermore, perimodiolar electrode placement does not result in better frequency discrimination. Objectives. We addressed three questions related to perimodiolar electrode placement. First, do patients implanted with the Contour™ electrode understand speech better than with an otherwise identical device that has a straight electrode? Second, do these groups have different frequency discrimination abilities? Third, is the distance of the electrode from the modiolus related to frequency discrimination ability? Subjects and methods. Contour™ and straight electrode users were matched on four important variables. We then tested these listeners on CNC word and HINT sentence identification tasks, and on a formant frequency discrimination task. We also examined X-rays and measured the distance of the electrodes from the modiolus to determine whether there is a relationship between this factor and frequency discrimination ability. Results. Both speech understanding and frequency discrimination abilities were similar for listeners implanted with the Contour™ vs a straight electrode. Furthermore, there was no linear relationship between electrode–modiolus distance and frequency discrimination ability. However, we did note a second-order relationship between these variables, suggesting that frequency discrimination is worse when the electrodes are either too close or too far away from the modiolus.

Predictions of formant-frequency discrimination in noise based on model auditory-nerve responses

To better understand how the auditory system extracts speech signals in the presence of noise, discrimination thresholds for the second formant frequency were predicted with simulations of auditory-nerve responses. These predictions employed either average-rate information or combined rate and timing information, and either populations of model fibers tuned across a wide range of frequencies or a subset of fibers tuned to a restricted frequency range. In general, combined temporal and rate information for a small population of model fibers tuned near the formant frequency was most successful in replicating the trends reported in behavioral data for formant-frequency discrimination. To explore the nature of the temporal information that contributed to these results, predictions based on model auditory-nerve responses were compared to predictions based on the average rates of a population of cross-frequency coincidence detectors. These comparisons suggested that average response rate (count) of cross-frequency coincidence detectors did not effectively extract important temporal information from the auditory-nerve population response. Thus, the relative timing of action potentials across auditory-nerve fibers tuned to different frequencies was not the aspect of the temporal information that produced the trends in formant-frequency discrimination thresholds.

Enhancement of temporal periodicity cues in cochlear implants: Effects on prosodic perception and vowel identification

Standard continuous interleaved sampling processing, and a modified processing strategy designed to enhance temporal cues to voice pitch, were compared on tests of intonation perception, and vowel perception, both in implant users and in acoustic simulations. In standard processing, 400 Hz low-pass envelopes modulated either pulse trains (implant users) or noise carriers (simulations). In the modified strategy, slow-rate envelope modulations, which convey dynamic spectral variation crucial for speech understanding, were extracted by low-pass filtering (32 Hz). In addition, during voiced speech, higher-rate temporal modulation in each channel was provided by 100% amplitude-modulation by a sawtooth-like wave form whose periodicity followed the fundamental frequency (F0) of the input. Channel levels were determined by the product of the lower- and higher-rate modulation components. Both in acoustic simulations and in implant users, the ability to use intonation information to identify sentences as question or statement was significantly better with modified processing. However, while there was no difference in vowel recognition in the acoustic simulation, implant users performed worse with modified processing both in vowel recognition and in formant frequency discrimination. It appears that, while enhancing pitch perception, modified processing harmed the transmission of spectral information.

Macaque thresholds for detecting increases in intensity: effects of formant structure

Macaque monkeys, like humans, are more sensitive to differences in formant frequency than to differences in the frequency of pure tones (see Sinnott et al. (1987) J. Comp. Psychol. 94, 401–415; Pfingst (1993) J. Acoust. Soc. Am. 93, 2124–2129; Prosen et al. (1990) J. Acoust. Soc. Am. 88, 2152–2158; Sinnott et al. (1985) J. Acoust. Soc. Am. 78, 1977–1985; Sinnott and Kreiter (1991) J. Acoust. Soc. Am. 89, 2421–2429; for summary, see May et al. (1996) Aud. Neurosci. 3, 135–162). In the discrimination of formant frequency, it appears that the relevant cue for macaque monkeys is relative level differences of the component frequencies (Sommers et al. (1992) J. Acoust. Soc. Am. 91, 3499–3510). To further explore the result of Sommers et al., we trained macaque monkeys ( Macaca fuscata) to report detection of a change in the spectral shape of multi-component harmonic complexes. Spectral shape changes were produced by the addition of intensity increments. When the amplitude spectrum of the comparison stimulus was modeled after the /ae/ vowel sound, thresholds for detecting a change from the comparison stimulus were lowest when intensity increments were added at spectral peaks. These results parallel previous data from human subjects, suggesting that both human and monkey subjects may process vowel spectra through simultaneous comparisons of component levels across the spectrum. When the subjects were asked to detect a change from a comparison stimulus with a flat amplitude spectrum, the subjects showed sensitivity that was relatively comparable to that of human subjects tested in other investigations (e.g. Zera et al. (1993) J. Acoust. Soc. Am. 93, 3431–3441). In additional experiments, neither increasing the dynamic range of the /ae/ spectrum nor dynamically varying the amplitude of the increment during the stimulus presentation reliably affected detection thresholds.

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.

Perceptual “vowel spaces” of cochlear implant users: Implications for the study of auditory adaptation to spectral shift

Cochlear implant (CI) users differ in their ability to perceive and recognize speech sounds. Two possible reasons for such individual differences may lie in their ability to discriminate formant frequencies or to adapt to the spectrally shifted information presented by cochlear implants, a basalward shift related to the implant's depth of insertion in the cochlea. In the present study, we examined these two alternatives using a method-of-adjustment (MOA) procedure with 330 synthetic vowel stimuli varying in F1 and F2 that were arranged in a two-dimensional grid. Subjects were asked to label the synthetic stimuli that matched ten monophthongal vowels in visually presented words. Subjects then provided goodness ratings for the stimuli they had chosen. The subjects' responses to all ten vowels were used to construct individual perceptual "vowel spaces." If CI users fail to adapt completely to the basalward spectral shift, then the formant frequencies of their vowel categories should be shifted lower in both F1 and F2. However, with one exception, no systematic shifts were observed in the vowel spaces of CI users. Instead, the vowel spaces differed from one another in the relative size of their vowel categories. The results suggest that differences in formant frequency discrimination may account for the individual differences in vowel perception observed in cochlear implant users.

Vowel formant discrimination in quiet and noise for natural speech

Everyday communication takes place in background noise. The purpose of this study is to investigate the effects of noise on formant discrimination for naturally spoken vowels. Our analysis of formant discrimination for synthetic vowels found that formant resolution could be accounted for by excitation pattern and specific loudness models [D. Kewley-Port and Y. Zheng, J. Acoust. Soc. Am. 103, 1654 (1998)]. It is expected that excitation pattern and specific loudness model can be extended to account for the formant discrimination in natural speech in both quiet and noise, even though natural speech has more variability than synthetic speech. The present study measured formant frequency discrimination in quiet and noise for normal-hearing listeners. Thresholds were measured as ΔF in natural speech for F1 and F2 for a set of vowels /I, ε, ʌ, æ/ spoken by a female talker. Noise conditions used a long-term averaged speech spectrum to shape the noise. The signal-to-noise ratio (SNR) was manipulated systematically from −6 to +6 dB. Results showed different masking patterns for F1 and F2 with performance approaching asymptote between 0 and +3 dB SNR. Results from an analysis of these data with a specific loudness pattern model will be presented. [Work supported by NIHDCD-02229.]

Extracting spectral envelopes: formant frequency matching between sounds on different and modulated fundamental frequencies.

The four experiments reported here measure listeners' accuracy and consistency in adjusting a formant frequency of one- or two-formant complex sounds to match the timbre of a target sound. By presenting the target and the adjustable sound on different fundamental frequencies, listeners are prevented from performing the task by comparing the absolute or relative levels of resolved spectral components. Experiment 1 uses two-formant vowellike sounds. When the two sounds have the same F0, the variability of matches (within-subject standard deviation) for either the first or the second formant is around 1%-3%, which is comparable to existing data on formant frequency discrimination thresholds. With a difference in F0, variability increases to around 8% for first-formant matches, but to only about 4% for second-formant matches. Experiment 2 uses sounds with a single formant at 1100 or 1200 Hz with both sounds on either low or high fundamental frequencies. The increase in variability produced by a difference in F0 is greater for high F0's (where the harmonics close to the formant peak are resolved) than it is for low F0's (where they are unresolved). Listeners also showed systematic errors in their mean matches to sounds with different high F0's. The direction of the systematic errors was towards the most intense harmonic. Experiments 3 and 4 showed that introduction of a vibratolike frequency modulation (FM) on F0 reduces the variability of matches, but does not reduce the systematic error. The experiments demonstrate, for the specific frequencies and FM used, that there is a perceptual cost to interpolating a spectral envelope across resolved harmonics.

Effects of stimulus uncertainty, consonantal context and training on formant frequency discrimination

Words in natural speech vary in their predictability, e.g., stimulus uncertainty ranges from low to very high across sentences. The ability to discriminate formants is strongly affected by longer phonetic context [Kewley-Port and Zheng (in press)]. This study investigates the effects of stimulus uncertainty from minimal to high uncertainty and the phonetic contexts /V/ or /bVd/. The primary formants were from four female vowels /ɪ, ε, æ, ə/. Using adaptive tracking, DLs for discriminating a small change in a formant was calculated in Delta Barks. In experiment 1, performance for five listeners, optimized by extensive training, began with minimal uncertainty, subsequently increasing uncertainty from 8- to 16- to 22 formants per block. Effects of higher uncertainty were less than expected, only decreasing performance by about 33%, although DLs for CVCs were 25% poorer than for isolated vowels. In experiment 2, performance in the 22-formant condition was tracked over 1 h for 37 listeners without formal laboratory training. DLs for untrained listeners were about 300% worse than for trained listeners, and comparable to untrained listeners in Kewley-Port and Zheng (in press). Results indicate that the effects of longer phonetic context degrade formant frequency discrimination more than higher stimulus uncertainty. [Work supported by NIHDCD-02229.]

聴覚障害者における日本語母音のホルマント周波数の弁別閾値について : 第2ホルマント弁別閾値を中心に

聴覚障害者における日本語母音のホルマント周波数の弁別閾値について : 第2ホルマント弁別閾値を中心に

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.

An ‘‘acoustic‐signature’’ model of vowel evolution.

Recent work in bioacoustics has emphasized the importance of cues to individual‐ and kinship‐identity in ‘‘signature’’ calls produced by many animal species, including nonhuman primates. Applying the source‐filter approach to sound production in monkeys and apes, it is proposed that low‐pitched, tonal calls may be significantly better‐suited to providing these indexical cues than are noisy or high‐pitched vocalizations. As the supralaryngeal vocal tract is relatively inflexible in many primates, harmonically rich calls produced by different individuals should exhibit stable, subtly distinctive spectral characteristics due to intraspecies variation in vocal tract size, shape, and tissue properties. Based on field studies of calls from baboons and rhesus monkeys, it is suggested that protohominids routinely uttered vowel‐like sounds long before the development of speech. Laboratory tests of pure‐tone and formant frequency discrimination in monkeys and humans further indicates that detailed formant‐related c...

Formant discrimination in femalelike vowels as a function of F1−F0 Bark distance

Hughes and Diehl [J. Acoust. Soc. Am. 95, 2978(A) (1994)] reported that discrimination of first formant frequency for both single and multiple formant stimuli was strongly influenced by both a formant/harmonic interaction and F1−F0 Bark distance. No evidence for a peak in discriminability near F1−F0=3.0–3.5 Bark was observed, however. The current study extended these findings to stimuli more characteristic of female talkers. Listeners performed a formant discrimination task on one of five series of four-formant stimuli varying in F1−F0 distance. F1 ranged from 3.2 to 7.7 Bark within a series, and F0 from 1.75 to 2.75 Bark between series. Preliminary results confirm both the strength of the formant/harmonic interaction and the lack of a peak in discriminability at F1−F0=3.0–3.5 Bark. Results also point up the need for a more adequate characterization of how formant frequency is represented in the auditory system. [Work supported by NIDCD.]