The perceptual segregation of simultaneous vowels with harmonic,shifted, or random components

This experiment was an investigation of the ability of listeners to identify the constituents of double vowels (pairs of synthetic vowels, presented concurrently and binaurally). Three variables were manipulated: (1) the size of the difference in FO between the constituents (0, 1/2, and 6 semitones); (2) the frequency relations among the sinusoids making up the constituents: harmonic, shifted (spaced equally in frequency but not integer multiples of the FO), and random; and (3) the relationship between the F0 contours imposed on the constituents: steady state, gliding in parallel, or gliding in opposite directions. It was assumed that, in the case of the gliding contours, the harmonics of each vowel would “trace out” their spectral envelope and potentially improve the definition of the formant locations. It was also assumed that the application of different FO contours would introduce differences in the direction of harmonic movement (common fate), thus aiding the perceptual segregation of the two vowels. The major findings were the following: (1) For harmonic constituents, a difference in FO leads to improved identification performance. Neither tracing nor common-fate differences add to the effect of pitch differences. (2) For shifted constituents, a difference between the spacing of the constituents also leads to improved performance. Formant tracing and common fate contribute some further improvement (3) For random constituents, tracing does not contribute, but common fate does.     

元音范畴知觉中特征分析和整合的时间进程

采用启动范式,在三个实验中通过操纵启动音和目标音的频谱相似度和时间间隔,考察了汉语听者元音范畴知觉中特征分析和整合的时间进程。结果发现随着启动音（从纯音、复合音到目标元音本身）和目标元音频谱相似度的增加,启动效应延续的时间越来越长。实验结果支持语音范畴知觉存在早期的声学特征分析和整合到后期的范畴知觉阶段,并为这些加工阶段的时间进程提供了初步的证据。     

非言语声音影响汉语听者言语声音的知觉

采用启动范式, 以汉语听者为被试, 考察了非言语声音是否影响言语声音的知觉。实验1考察了纯音对辅音范畴连续体知觉的影响, 结果发现纯音影响到辅音范畴连续体的知觉, 表现出频谱对比效应。实验2考察了纯音和复合音对元音知觉的影响, 结果发现与元音共振峰频率一致的纯音或复合音加快了元音的识别, 表现出启动效应。两个实验一致发现非言语声音能够影响言语声音的知觉, 表明言语声音知觉也需要一个前言语的频谱特征分析阶段, 这与言语知觉听觉理论的观点一致。     

The role of timbre in the segregation of simultaneous voices with intersecting F0 contours

When the fundamental frequency (F₀) contours of two speakers’ voices intersect, the listener is presented with a problem. The listener must decide which of the F₀ contours emerging from the intersection is a continuation of which contour entering the intersection: have the F₀ contours crossed or merely approached and parted? In the present experiment, subjects listened to two simultaneous diphthong-like sounds with F₀ contours that either approached and diverged or crossed over. The task was to report whether the pitches “crossed” or “bounced” away from each other. Despite the changing timbres of the two sounds, the subjects were able to discriminate crossing and bouncing F₀s, provided that the timbres of the vowels differed at the moment when their F₀s were the same. When the timbres were the same, the subjects could not make the discrimination and tended to hear a bouncing percept. These results are consistent with the idea that listeners use continuity of timbre rather than continuity of F₀ movement to disambiguate F₀ intersections.     

辅音和元音知觉中的启动效应差异

采用启动范式,在两个实验中分别考察了辅音范畴和元音范畴知觉中的启动效应。启动音是纯音和目标范畴本身,目标音是辅音范畴和元音范畴连续体。结果发现辅音范畴连续体知觉的范畴反应百分比受到纯音和言语启动音影响,辅音范畴知觉的反应时只受言语启动音影响;元音范畴连续体知觉的范畴反应百分比不受两种启动音影响,但元音范畴知觉的反应时受到言语启动音影响。实验结果表明辅音范畴和元音范畴知觉中的启动效应存在差异,这为辅音和元音范畴内在加工机制的差异提供了新证据。     

Cross-modal speech perception in adults and infants using nonspeech auditory stimuli.

Adults and infants were tested for the capacity to detect correspondences between nonspeech sounds and real vowels. The /i/ and /a/ vowels were presented in 3 different ways: auditory speech, silent visual faces articulating the vowels, or mentally imagined vowels. The nonspeech sounds were either pure tones or 3-tone complexes that isolated a single feature of the vowel without allowing the vowel to be identified. Adults perceived an orderly relation between the nonspeech sounds and vowels. They matched high-pitched nonspeech sounds to /i/ vowels and low-pitched nonspeech sounds to /a/ vowels. In contrast, infants could not match nonspeech sounds to the visually presented vowels. Infants' detection of correspondence between auditory and visual speech appears to require the whole speech signal; with development, an isolated feature of the vowel is sufficient for detection of the cross-modal correspondence.     

Effects of phase changes in low-numbered harmonics on the internal representation of complex sounds

A series of experiments investigated the effect of phase changes in lownumbered single harmonics in target sounds that were either synthesized steady-state vowels or periodic signals having only a single formant. A matching procedure was used in which subjects selected a sound along a continuum differing in first formant frequency in order to get the best match with the target sound; perceptual effects of the phase manipulations in the target were detected as a change in the matched first formant frequency. Stimuli had to contain at least three harmonics to produce the effect, but it did not require a particular starting phase of the components. A suppression phenomenon is discussed, in which phase changes alter the phase-locking characteristics of auditory fibres tuned to low-numbered harmonics.     

Perceptual grouping affects pitch judgments across time and frequency

Pitch, the perceptual correlate of fundamental frequency (F0), plays an important role in speech, music, and animal vocalizations. Changes in F0 over time help define musical melodies and speech prosody, while comparisons of simultaneous F0 are important for musical harmony, and for segregating competing sound sources. This study compared listeners' ability to detect differences in F0 between pairs of sequential or simultaneous tones that were filtered into separate, nonoverlapping spectral regions. The timbre differences induced by filtering led to poor F0 discrimination in the sequential, but not the simultaneous, conditions. Temporal overlap of the two tones was not sufficient to produce good performance; instead performance appeared to depend on the two tones being integrated into the same perceptual object. The results confirm the difficulty of comparing the pitches of sequential sounds with different timbres and suggest that, for simultaneous sounds, pitch differences may be detected through a decrease in perceptual fusion rather than an explicit coding and comparison of the underlying F0s.     

Comparison of associations to vowel speech sounds by English and Spanish speakers

Many psycholinguists have studied associations to vowel speech sounds. It appears that associations involving brightness and size are related to the manner in which the vowels are articulated. That is, high front vowels are judged to be bright and small, and low back vowels are judged to be dim and large. In an extension of a study by Greenberg and Jenkins (1966), 40 English-speaking and 40 Spanish-speaking adults rated nine audiotaped vowel sounds on 23 dimensions. The front-back distinction was again found for both groups. In addition, ratings for all nine vowels were similar for the two groups, which has implications for the cross-cultural universality of these associations.     

Exploration of vocal tract properties during serial production of vowels by full term and preterm infants

This study examines the acoustic characteristics of individual vowels and those produced in sequences of three or more during vocal play by full term and preterm at age 6 months. Laboratory and home audiotape recordings of infant vowel sounds were made and digitized for acoustic analysis. Of interest was whether, during production of vowel sequences compared to those produced singly, infants explored the relation between tongue height and tongue advancement, as measured acoustically by the first formant (F1) and second formant (F2) frequencies, respectively. In both groups of infants, the region of F1-F2 space for individually produced vowels was significantly greater than for vowels produced in sequence. High correlation coefficients for F1 and F2 during exploration of vowels produced in sequence were apparent in full term, but not preterm infants. The data support the claim that vowels produced in sequence occupy a more limited region of the vocal tract than those produced singly, and that infants explore the characteristics of their vocalizations within sequences.     

The perception of back vowels: Centre of gravity hypothesis

According to the formant centre of gravity (FCOG) hypothesis, two vowel formants in close proximity are merged during perceptual analysis, and their contribution to vowel quality depends on the centre of gravity of the formant cluster. Findings consistent with this hypothesis are that two formants can be replaced by a single formant of intermediate centre frequency, provided their separation is less than 3-3.5 Bark; and that changes in their relative amplitudes produce systematic shifts in vowel quality. In Experiment 1, listeners adjusted the frequencies of F1 and F2 in a synthesized 6-formant vowel (with the F1-F2 separation fixed at 250 Hz, i.e. less than 3 Bark) to find the best phonetic match to a reference vowel with modified formant amplitudes. Contrary to FCOG predictions, F2 attenuation did not produce lower frequency matches. Raising the amplitude of F2 led to predicted upward shifts in formant frequencies of the matched vowel, but with increased variability of matches for some stimuli. In Experiment 2, listeners identified synthesized vowels with a range of separations of F1 and F2. Formant amplitude manipulations had no effect on listeners' judgements when the fundamental frequency was low (125 Hz). Small shifts in vowel quality appeared for stimuli with a high fundamental (250 Hz), but the shifts were significantly larger for F1-F2 separations greater than 3.5 Bark. These effects of formant amplitude are qualitatively different from those observed with single-formant vowels and are generally incompatible with a formant-averaging mechanism.     

The effect of vibrato on the recognition of masked vowels

Five experiments on the identifiability of synthetic vowels masked by wideband sounds are reported. In each experiment, identification thresholds (signal/masker ratios, in decibels) were measured for two versions of four vowels: a vibrated version, in which FO varied sinusoidally around 100 Hz; and a steady version, in which F0 was fixed at 100 Hz. The first three experiments were performed on naive subjects. Experiment 1 showed that for maskers consisting of bursts of pink noise, vibrato had no effect on thresholds. In Experiment 2, where the maskers were periodic pulse trains with an F0 randomly varied between 120 and 140 Hz from trial to trial, vibrato slightly improved thresholds when the sound pressure level of the maskers was 40 dB, but had no effect for 65-dB maskers. In Experiment 3, vibrated rather than steady pulse trains were used as maskers; when these maskers were at 40 dB, the vibrated versions of the vowels were slightly less identifiable than their steady versions; but, as in Experiment 2, vibrato had no effect when the maskers were at 65 dB. Experiment 4 showed that the unmasking effect of vibrato found in Experiment 2 disappeared in subjects trained in the identification task. Finally, Experiment 5 indicated that in trained listeners, vibrato had no influence on identification performance even when the maskers and the vowels had synchronous onsets and offsets. We conclude that vibrating a vowel masked by a wideband sound can affect its identification threshold, but only for tonal maskers and in untrained listeners. This effect of vibrato should probably be considered as a Gestalt phenomenon originating from central auditory mechanisms.     

Intrinsicf0 differences in spoken and sung vowels and their perception by listeners

We explore how listeners perceive distinct pieces of phonetic information that are conveyed in parallel by the fundamental frequency (f0) contour of spoken and sung vowels. In a first experiment, we measured differences inf0 of /i/ and /a/ vowels spoken and sung by unselected undergraduate participants. Differences in “intrinsicf0” (withf0 of /i/ higher than of /a/) were present in spoken and sung vowels; however, differences in sung vowels were smaller than those in spoken vowels. Four experiments tested a hypothesis that listeners would not hear the intrinsicf0 differences as differences in pitch on the vowel, because they provide information, instead, for production of a closed or open vowel. The experiments provide clear evidence of “parsing” of intrinsicf0 from thef0 that contributes to perceived vowel pitch. However, only some conditions led to an estimate of the magnitude of parsing that closely matched the magnitude of produced intrinsicf0 differences.     

Disruption of visual short-term memory by changing-state auditory stimuli: The role of segmentation

Typically, serial recall performance can be disrupted by the presence of an irrelevant stream of background auditory stimulation, but only if the background stream changes over time (the auditory changing-state effect). It was hypothesized that segmentation of the auditory stream is necessary for changing state to be signified. In Experiment 1, continuous random pitch glides failed to disrupt serial recall, but glides interrupted regularly by silence brought about the usual auditory changing-state effect. In Experiment 2, a physically continuous stream of synthesized vowel sounds was found to have disruptive effects. In Experiment 3, the technique of auditory induction showed that preattentive organization rather than critical features of the sound could account for the disruption by glides. With pitch glides, silence plays a preeminent role in the temporal segmentation of the sound stream, but speech contains corr-elated-time-varying changes in frequency and amplitude that make silent intervals superfluous.     

Spectral fissioning in phonemic transformations

Listeners presented with a repeated sequence of brief (30- to 100-msec) steady-state vowels hearphonemic transformations—they cannot identify the vowels, but they perceive two simultaneous utterances that differ in both phonemic content and timbre (Warren, Bashford, & Gardner, 1990). These utterances consist of either English words or syllables that occur in English words. In the present study, we attempted to determine whether the two percepts represent alternative interpretations of the same formant structures, or whether different portions of the vowels are used for each verbal organization. It was found that separate spectral regions are employed for each verbal form; Components below 1500 Hz were generally used for one form, and components above 1500 Hz for the other. Hypotheses are offered concerning the processes responsible for the verbal organization of the vowel sequences and for the splitting into two spectrally limited forms. It appears that the tendency to organize spectral regions separately competes with, and can overcome, the tendency to integrate the different spectral components of speech into a single auditory image. A contralateral induction paradigm was used in a procedure designed to quantitatively evaluate these opposing forces of spectral fission and fusion.     

Categories and context in the perception of isolated steady-state vowels

The noncategorical perception of isolated vowels has been attributed to the availability of auditory memory in discrimination. In our first experiment, using vowels from an /i/-/I/epsilon) continuum in a same-different (AX) task and comparing the results with predictions derived from a separate identification test, we demonstrated that vowels are perceived more nearly categorically if auditory memory is degraded by extending the interstimulus interval and/or filling it with irrelevant vowel sounds. In a second experiment, we used a similar paradigm, but in addition to presenting a separate identification test, we elicited labeling responses to the AX pairs used in the discrimination task. We found that AX labeling responses predicted discrimination performance quite well, regardless of whether auditory memory was available, whereas the predictions from the separate identification test were more poorly matched by the obtained data. The AX labeling reponses showed large contrast effects (both proactive and retroactive) that were greatly reduced when auditory memory was interfered with. We conclude from the presence of these contrast effects that vowels are not perceived categorically (that is, absolutely). However, it seems that by taking the effects of context into account properly, discrimination performance can be quite accurately predicted from labeling data, suggesting that vowel discrimination, like consonant discrimination, may be mediated by phonetic labels.     

When acoustic sequences are not perceptual sequences: The global perception of auditory patterns

Warren, Bashford, and Gardner (1990) found that when sequences consisting of 10 40-msec steady-state vowels were presented in recycled format, minimal changes in order (interchanging the position of two adjacent phonemes) produced easily recognizable differences in verbal organization, even though the vowel durations were well below the threshold for identification of order. The present study was designed to determine if this ability to discriminate between different arrangements of components is limited to speech sounds subject to verbal organization, or if it reflects a more general auditory ability. In the first experiment. 10 40-msec sinusoidal tones were substituted for the vowels; it was found that the easy discrimination of minimal changea in order is not limited to speech sounds. A second experiment substituted 10 40-msec frozen noise segments for the vowels. The succession of noise segments formed a 400-msec frozen noise pattern that cannot be considered as a sequence of individual sounds, as can the succession of vowels or tones. Nevertheless, listeners again could discriminate between patterns differing.only in the order of two adjacent 40-msec segments. These results, together with other evidence, indicate that it is not necessary foracoustic sequences of brief items (such as phonemes and tones) to be processed asperceptual sequences (that is, as a succession of discrete identifiable sounds) for different arrangements to be discriminated. Instead, component acoustic elements form distinctive “temporal compounds,” which permit listeners to distinguish between different arrangements of portions of an acoustic pattern without the need for segmentation into an ordered series of component items. Implications for models dealing with the recognition of speech and music are discussed.     

Mommy is only happy! Dutch mothers’ realisation of speech sounds in infant-directed speech expresses emotion,not didactic intent

Exaggeration of the vowel space in infant-directed speech (IDS) is well documented for English, but not consistently replicated in other languages or for other speech-sound contrasts. A second attested, but less discussed, pattern of change in IDS is an overall rise of the formant frequencies, which may reflect an affective speaking style. The present study investigates longitudinally how Dutch mothers change their corner vowels, voiceless fricatives, and pitch when speaking to their infant at 11 and 15 months of age. In comparison to adult-directed speech (ADS), Dutch IDS has a smaller vowel space, higher second and third formant frequencies in the vowels, and a higher spectral frequency in the fricatives. The formants of the vowels and spectral frequency of the fricatives are raised more strongly for infants at 11 than at 15 months, while the pitch is more extreme in IDS to 15-month olds. These results show that enhanced positive affect is the main factor influencing Dutch mothers’ realisation of speech sounds in IDS, especially to younger infants. This study provides evidence that mothers’ expression of emotion in IDS can influence the realisation of speech sounds, and that the loss or gain of speech clarity may be secondary effects of affect.     

Vowel categorization during word recognition in bilingual toddlers

Toddlers’ and preschoolers’ knowledge of the phonological forms of words was tested in Spanish-learning, Catalan-learning, and bilingual children. These populations are of particular interest because of differences in the Spanish and Catalan vowel systems: Catalan has two vowels in a phonetic region where Spanish has only one. The proximity of the Spanish vowel to the Catalan ones might pose special learning problems. Children were shown picture pairs; the target picture’s name was spoken correctly, or a vowel in the target word was altered. Altered vowels either contrasted with the usual vowel in Spanish and Catalan, or only in Catalan. Children’s looking to the target picture was used as a measure of word recognition. Monolinguals’ word recognition was hindered by within-language, but not non-native, vowel changes. Surprisingly, bilingual toddlers did not show sensitivity to changes in vowels contrastive only in Catalan. Among preschoolers, Catalan-dominant bilinguals but not Spanish-dominant bilinguals revealed mispronunciation sensitivity for the Catalan-only contrast. These studies reveal monolingual children’s robust knowledge of native-language vowel categories in words, and show that bilingual children whose two languages contain phonetically overlapping vowel categories may not treat those categories as separate in language comprehension.     

Perception of vocal effort and distance from the speaker on the basis of vowel utterances

The sound pressure level of vowels reflects several nonlinguistic and linguistic factors: distance from the speaker, vocal effort, and vowel quality. Increased vocal effort also involves the emphasis of higher frequency components and increases in F0 and F1. This should allow listeners to distinguish it from decreased distance, which does not have these additional effects. It is shown that listeners succeed in doing so on the basis of single vowels if phonated, but not if whispered, and that they compensate for most of the between-vowel variation in level. The results obtained when listeners had to estimate vocal effort as well as distance suggest that an analysis of an utterance takes place at an early stage in auditory processing, before memories of episodes are stored.