Relative and Absolute Judgments of Speech Rate from Masked and Content-Standard Stimuli The Influence of Vocal Frequency and Intensity

In two previous studies, the perception of speech rate was found to be positively related to the vocal frequency and intensity of speech. In those studies, a single sample of spontaneous, content-masked speech was used to produce nine stimuli by factorially varying three levels of each vocal frequency and intensity, while controlling the actual speech rate of the stimuli. Participants were asked to judge each stimulus, preceded by a standard, “anchoring,” stimulus as to its speech rate, pitch, loudness, and duration. The purpose of the three studies reported here was to examine the generalizability of the previous findings by using stimuli that were nonmasked and/or were not preceded by an anchoring stimulus. In each study, nine speech stimuli were prepared, as described above, and participants were asked to make judgments about the rate, pitch, loudness, and duration of each stimulus. In the first study, the stimuli were masked but were not preceded by an anchoring stimulus. In the second study, participants listened to content-standard speech stimuli preceded by an anchoring stimulus. Finally, in the third study, content-standard stimuli without an anchoring stimulus were used. In addition, studies two and three used speech segments of a male and a female speaker. The findings from the three studies replicated the central findings of the previous studies. They suggest, in other words, that rate perception of speech is indeed influenced by vocal frequency and, to some extent, by intensity, and that these relationships are not materially altered by the speakers'gender.     

Categorical results do not imply categorical perception

Categorical perception refers to the ability to discriminate between- but not within-category differences along a stimulus continuum. Although categorical perception was thought to be unique to speech, recent studies have yielded similar results with nonspeech continua. The results are usually interpreted in terms of categorical, as opposed to continuous, perception of both speech and nonspeech continua. In contrast, we argue that these continua are perceived continuously, although they are characterized by relatively large increases in discrim-inability near the category boundary. To support this argument, the amplitude rise time of a tone was varied to produce either an increase or a decrease in the intensity during the initial portion of the tone. A bipolar continuum of onset times increasing and decreasing in amplitude yielded traditional categorical results. However, when only half of this continuum was tested, subjects perceived the same sounds continuously. The finding of traditional categorical results along the bipolar continuum, when the sounds were shown to be perceived continuously in another context, argues against the use of traditional categorical results as evidence for categorical perception.     

The ABCs of categorical perception

Studies of speech perception first revealed a surprising discontinuity in the way in which stimulus values on a physical continuum are perceived. Data which demonstrate the effect in nonspeech modes have challenged the contention that categorical perception is a hallmark of the speech mode, but the psychophysical models that have been proposed have not resolved the issues raised by empirical findings. This study provides data from judgments of four sensory continua, two visual and two tactual-kinesthetic, which show that the adaptation level for a set of stimuli serves as a category boundary whether stimuli on the continuum differ by linear or logarithmic increments. For all sensory continua studied, discrimination of stimuli belonging to different perceptual categories was more accurate than discrimination of stimuli belonging to the same perceptual category. Moreover, shifts in the adaptation level produced shifts in the location of the category boundary. The concept of Adaptation-level Based Categorization (ABC) provides a unified account of judgmental processes in categorical perception without recourse to post hoc constructs such as implicit anchors or external referents.     

Categorical perception of race

Traditionally, research demonstrating categorical perception (CP) has assumed that CP occurs only in cases where natural continua are divided categorically by long-term learning or innate perceptual programming. More recent research suggests that this may not be true, and that even novel continua between novel stimuli such as unfamiliar faces can show CP effects as well. Given this, we ask whether CP is dependent solely on the representation of individual stimuli, or whether stimulus categories themselves can also cause CP. Here, we test the hypothesis that continua between individual faces that cross the categorical boundary between races show an enhanced CP effect. We find that continua running from a black face to a white face do, indeed, show stronger CP effects than continua between two black faces or two white faces. This suggests that CP effects are enhanced when continua run between two distinctly represented individual stimuli, and are further enhanced when those individuals are, in turn, members of different stimulus categories.     

Categorical perception of nonspeech chirps and bleats

Mattingly, Liberman, Syrdal, and Halwes, (1971) claimed to demonstrate that subjects cannot classify nonspeech chirp and bleat continua, but that they can classify into three categories a syllable place continuum whose variation is physically identical to the nonspeech chirp and bleat continua. This finding for F2 transitions, as well as similar findings for F3 transitions, has been cited as one source of support for theories that different modes or modules underlie the perception of speech and nonspeech acoustic stimuli. However, this pattern of finding for speech and nonspeech continua may be the result of research methods rather than a true difference in subject ability. Using tonal stimuli based on the nonspeech stimuli of Mattingly et al., we found that subjects, with appropriate practice, could classify nonspeech chirp, short bleat, and bleat continua with boundaries equivalent to the syllable place continuum of Mattingly et al. With the possible exception of the higher frequency boundary for both our bleats and the Mattingly syllables, ABX discrimination peaks were clearly present and corresponded in location to the given labeling boundary.     

Adaptation of speech by nonspeech: evidence for complex acoustic cue detectors

Three selective adaptation experiments were run, using nonspeech stimuli (music and noise) to adapt speech continua ([ba]-[wa] and [cha]-[sha]). The adaptors caused significant phoneme boundary shifts on the speech continua only when they matched in periodicity: Music stimuli adapted [ba]-[wa], whereas noise stimuli adapted [cha]-[sha]. However, such effects occurred even when the adaptors and test continua did not match in other simple acoustic cues (rise time or consonant duration). Spectral overlap of adaptors and test items was also found to be unnecessary for adaptation. The data support the existence of auditory processors sensitive to complex acoustic cues, as well as units that respond to more abstract properties. The latter are probably at a level previously thought to be phonetic. Asymmetrical adaptation was observed, arguing against an opponent-process arrangement of these units. A two-level acoustic model of the speech perception process is offered to account for the data.     

Acoustical correlates of the perception of speech rate: An experimental investigation

The purpose of the study was to investigate the influence of vocal frequency and vocal intensity upon the perception of speech rate at three levels of actual speech rate. A single sample of spontaneous speech was electronically varied to produce nine stimulus segments that factorially combined three levels each of vocal frequency and intensity. The nine stimuli were recorded such that preceding each was the original segment that served as the standard with which each of the nine stimuli was to be compared. The speech rate of the set of nine stimulus pairs was then electronically altered to obtain a slow set, a moderate set, and a fast set, although the duration of every segment in the three sets was 20 seconds. The sets were rated by different groups of judges in terms of four 7-point scales that measured perceived speech rate, pitch, loudness, and perceived duration. The results indicate that the perception of speech rate is positively related to vocal frequency and intensity at each of the three actual speech rates, and suggest that these relationships are a function of the repeated experience of almost always hearing such covariation in spontaneously occurring speech.The authors are indebted to the Language Laboratory of the University of Maryland Baltimore County and are grateful for the generous amount of computer time provided by the Computer Centers of the Baltimore County and College Park campuses of the university. They are also indebted to Mr. George J. Johnson, Jr., for the design and construction of the instrument used in the study, to Drs. Edwin Susskind and Jahathan Finkelstein for their active concern about the meaning of the results, and to Dr. Klaus Scherer for his very helpful critique.     

Measuring the difference limen for identification of order of onset for complex auditory stimuli

The approximately 20-msec perceptual threshold for identifying order of onset for components of auditory stimuli has been considered both as a possible factor contributing to the perception of voicing contrasts in speech and as no more than a methodological artifact. In the present research, we investigate the identification of the temporal order of onset of spectral components in terms of the first of a sequence of thresholds for complex stimuli (modeled after consonant-vowel [CV] syllables) that vary in degree of onset. The results provide clear evidence that the difference limen (DL) for discriminating differences in onset time follows predictions based on a fixed perceptual threshold or limit at relatively short onset differences. Furthermore, the DL seems to be a function of context coding of stimulus information, with both the DL and absolute threshold probably reflecting limits on the effective perception and coding of the short-term stimulus spectrum.     

Phonological abstraction without phonemes in speech perception

Recent evidence shows that listeners use abstract prelexical units in speech perception. Using the phenomenon of lexical retuning in speech processing, we ask whether those units are necessarily phonemic. Dutch listeners were exposed to a Dutch speaker producing ambiguous phones between the Dutch syllable-final allophones approximant [r] and dark [l]. These ambiguous phones replaced either final /r/ or final /l/ in words in a lexical-decision task. This differential exposure affected perception of ambiguous stimuli on the same allophone continuum in a subsequent phonetic-categorization test: Listeners exposed to ambiguous phones in /r/-final words were more likely to perceive test stimuli as /r/ than listeners with exposure in /l/-final words. This effect was not found for test stimuli on continua using other allophones of /r/ and /l/. These results confirm that listeners use phonological abstraction in speech perception. They also show that context-sensitive allophones can play a role in this process, and hence that context-insensitive phonemes are not necessary. We suggest there may be no one unit of perception.     

Neural network models of categorical perception

Studies of the categorical perception (CP) of sensory continua have a long and rich history in psychophysics. In 1977, Macmillan, Kaplan, and Creelman introduced the use of signal detection theory to CP studies. Anderson and colleagues simultaneously proposed the first neural model for CP, yet this line of research has been less well explored. In this paper, we assess the ability of neural-network models of CP to predict the psychophysical performance of real observers with speech sounds and artificial/novel stimuli. We show that a variety of neural mechanisms are capable of generating the characteristics of CP. Hence, CP may not be a special model of perception but an emergent property of any sufficiently powerful general learning system.     

Individual variability in the perception of cues to place contrasts in initial stops

Synthetic continua of two minimal pairs, BAIT-DATE and DATE-GATE, closely modeled on natural utterances by a female speaker, were presented to a group of 16 listeners for identification in full-cue and reduced-cue conditions. Grouped results showed that categorization curves for full- and reduced-cue conditions differed significantly in both contrasts. However, an averaging of results obscures marked variability in labeling behavior. Some listeners showed large changes in categorization between the full- and reduced-cue conditions, whereas others showed relatively small or no changes. In a follow-up study, perception of the BAIT-DATE contrast was compared with the perception of a highly stylized BA-DA continuum. A smaller degree of intersubject and between-condition variability was found for these less complex synthetic stimuli. The amount of variability found in the labeling of speech contrasts may be dependent on cue salience, which will be determined by the speech pattern complexity of the stimuli and by the vowel environment.     

Categorical perception occurs in newly learned faces, other-race faces, and inverted faces

On the basis of findings that categorical perception (CP) is possible in complex visual stimuli such as faces, the present study tested for CP on continua between unfamiliar face pairs. Results indicate that CP can be observed for unfamiliar faces, in both familiar (same-race) and unfamiliar (other-race) groups. In addition, significant CP effects were observed in inverted faces. Finally, half-continua were tested where midpoint stimuli became endpoints. This was done to ensure that stimulus artifacts did not account for the observed CP effects. Consistent with the perceptual rescaling associated with CP, half-continua showed a rescaled CP effect. We argue that these CP effects are based on the rapid acquisition of perceptual equivalence classes.     

Neurological evidence in support of a specialized phonetic processing module

Event-related potentials (ERPs) were utilized to study brain activity while subjects listened to speech and nonspeech stimuli. The effect of duplex perception was exploited, in which listeners perceive formant transitions that are isolated as nonspeech "chirps," but perceive formant transitions that are embedded in synthetic syllables as unique linguistic events with no chirp-like sounds heard at all (Mattingly et al., 1971). Brain ERPs were recorded while subjects listened to and silently identified plain speech-only tokens, duplex tokens, and tone glides (perceived as "chirps" by listeners). A highly controlled set of stimuli was developed that represented equivalent speech and nonspeech stimulus tokens such that the differences were limited to a single acoustic parameter: amplitude. The acoustic elements were matched in terms of number and frequency of components. Results indicated that the neural activity in response to the stimuli was different for different stimulus types. Duplex tokens had significantly longer latencies than the pure speech tokens. The data are consistent with the contention of separate modules for phonetic and auditory stimuli.     

Potential perceptual bases for successful use of a vibrotactile speech perception aid

This paper examines the possibility that perception of vibrotactile speech stimuli is enhanced in adults with early and life-long use of hearing aids. We present evidence that vibrotactile aid benefit in adults is directly related to the age at which the hearing aid was fitted and the duration of its use. The stimulus mechanism responsible for this effect is hypothesized to be long-term vibrotactile stimulation by high powered hearing aids. We speculate on possible mechanisms for enhanced vibrotactile speech perception as the result of hearing aid use: (1) long-term experience receiving degraded or impoverished speech stimuli results in a speech processing system that is more effective for novel stimuli, independent of perceptual modality; and/or (2) long-term sensory/perceptual experience causes neural changes that result in more effective delivery of speech information via somatosensory pathways.     

Acoustic cues for the perception of place of articulation in aphasia

Two experiments assessed the abilities of aphasic patients and nonaphasic controls to perceive place of articulation in stop consonants. Experiment I explored labeling and discrimination of [ba, da, ga] continua varying in formant transitions with or without an appropriate burst onset appended to the transitions. Results showed general difficulty in perceiving place of articulation for the aphasic patients. Regardless of diagnostic category or auditory language comprehension score, discrimination ability was independent of labeling ability, and discrimination functions were similar to normals even in the context of failure to reliably label the stimuli. Further there was less variability in performance for stimuli with bursts than without bursts. Experiment II measured the effects of lengthening the formant transitions on perception of place of articulation in stop consonants and on the perception of auditory analogs to the speech stimuli. Lengthening the transitions failed to improve performance for either the speech or nonspeech stimuli, and in some cases, reduced performance level. No correlation was observed between the patient's ability to perceive the speech and nonspeech stimuli.     

Effects of audio-visual integration on the detection of masked speech and non-speech sounds

Integration of simultaneous auditory and visual information about an event can enhance our ability to detect that event. This is particularly evident in the perception of speech, where the articulatory gestures of the speaker's lips and face can significantly improve the listener's detection and identification of the message, especially when that message is presented in a noisy background. Speech is a particularly important example of multisensory integration because of its behavioural relevance to humans and also because brain regions have been identified that appear to be specifically tuned for auditory speech and lip gestures. Previous research has suggested that speech stimuli may have an advantage over other types of auditory stimuli in terms of audio-visual integration. Here, we used a modified adaptive psychophysical staircase approach to compare the influence of congruent visual stimuli (brief movie clips) on the detection of noise-masked auditory speech and non-speech stimuli. We found that congruent visual stimuli significantly improved detection of an auditory stimulus relative to incongruent visual stimuli. This effect, however, was equally apparent for speech and non-speech stimuli. The findings suggest that speech stimuli are not specifically advantaged by audio-visual integration for detection at threshold when compared with other naturalistic sounds.     

汉语语音范畴性知觉及其发展

范畴性是言语知觉的一个显著特征,长期以来一直受到研究者的普遍关注。但汉语不同语音特征的范畴性知觉特点及其发展模式迄今为止还很少有研究涉及。本研究利用语音合成的方法分别改变辅音的送气/不送气特征和声调的基频曲线,生成语音刺激连续体,采用范畴性知觉的经典研究范式探讨了汉语正常成人被试嗓音启动时间（Voice onset time,VOT）和声调范畴性知觉的特点及不同年龄儿童的发展模式。研究结果表明：（1）成人被试对VOT和声调的知觉是范畴性的;（2）对于汉语声调特征,6岁儿童已经具有类似成人的范畴性知觉能力;而在VOT这一维度上,范畴知觉能力随着年龄发展不断精细化,但7岁儿童也尚未达到成年人的敏感程度,说明汉语VOT和声调这两个不同的语音特征经历了不同的发展模式。     

Context Effects on Musical Chord Categorization: Different Forms of Top‐Down Feedback in Speech and Music?

A critical issue in perception is the manner in which top-down expectancies guide lower level perceptual processes. In speech, a common paradigm is to construct continua ranging between two phonetic endpoints and to determine how higher level lexical context influences the perceived boundary. We applied this approach to music, presenting participants with major/minor triad continua after brief musical contexts. Two experiments yielded results that differed from classic results in speech perception. In speech, context generally expands the category of the expected stimuli. We found the opposite in music: The major/minor boundary shifted toward the expected category, contracting it. Together, these experiments support the hypothesis that musical expectancy can feed back to affect lower-level perceptual processes. However, it may do so in a way that differs fundamentally from what has been seen in other domains.     

Adaptation of the category boundary between speech and nonspeech: A case against feature detectors

Two experiments were performed employing acoustic continua which change from speech to nonspeech. The members of one continuum, synthesized on the Pattern Playback, varied in the bandwidths of the first three formants in equal steps of change, from the vowel /α/ to a nonspeech buzz. The other continuum, achieved through digital synthesis, varied in the bandwidths of the first five formants, from the vowel /æ/ to a buzz. Identification and discrimination tests were carried out to establish that these continua were perceived categorically. Perceptual adaptation of these continua revealed shifts in the category boundaries comparable to those previously reported for speech sounds. The results were interpreted as suggesting that neither phonetic nor auditory feature detectors are responsible for perceptual adaptation of speech sounds, and that feature detector accounts of speech perception should therefore be reconsidered.     

Explicit authenticity and stimulus features interact to modulate BOLD response induced by emotional speech

Context has been found to have a profound effect on the recognition of social stimuli and correlated brain activation. The present study was designed to determine whether knowledge about emotional authenticity influences emotion recognition expressed through speech intonation. Participants classified emotionally expressive speech in an fMRI experimental design as sad, happy, angry, or fearful. For some trials, stimuli were cued as either authentic or play-acted in order to manipulate participant top-down belief about authenticity, and these labels were presented both congruently and incongruently to the emotional authenticity of the stimulus. Contrasting authentic versus play-acted stimuli during uncued trials indicated that play-acted stimuli spontaneously up-regulate activity in the auditory cortex and regions associated with emotional speech processing. In addition, a clear interaction effect of cue and stimulus authenticity showed up-regulation in the posterior superior temporal sulcus and the anterior cingulate cortex, indicating that cueing had an impact on the perception of authenticity. In particular, when a cue indicating an authentic stimulus was followed by a play-acted stimulus, additional activation occurred in the temporoparietal junction, probably pointing to increased load on perspective taking in such trials. While actual authenticity has a significant impact on brain activation, individual belief about stimulus authenticity can additionally modulate the brain response to differences in emotionally expressive speech.