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.     

More adaptation of speech by nonspeech

Three experiments tested Samuel and Newport's (1979) hypothesis that the perceptual system sorts its input on the basis of its spectral quality (periodic vs. aperiodic). In Experiment 1, repeated presentation of a shaped white-noise segment (aperiodic) produced a labeling shift on a /ja-za/ continuum (primarily aperiodic); two periodic adaptors produced no effect, supporting Samuel and Newport's hypothesis. The second experiment replicated these results and showed that the nonspeech adaptor produced almost as much adaptation as the test series' endpoint /za). In addition, using several mixtures of periodic and aperiodic adaptors indicated that the aperiodic component dominates adaptation effects for /ja-za/. A final experiment, using a similarity rating task, confirmed that subjects group /za/ with unvoiced fricatives rather than with other voiced consonants. The results thus indicate that the perceptual system is sensitive to whether the input is primarily periodic or aperiodic, regardless of whether it is speech or nonspeech.     

Insights from a failure of selective adaptation: syllable-initial and syllable-final consonants are different

Selective adaptation with a syllable-initial consonant fails to affect perception of the same consonant in syllable-final position, and vice versa. One account of this well-replicated result invokes a cancellation explanation: with the place-of-articulation stimuli used, the pattern of formant transitions switches according to syllabic position, allowing putative phonetic-level effects to be opposed by putative acoustic-level effects. Three experiments tested the cancellation hypothesis by preempting the possibility of acoustic countereffects. In Experiment 1, the test syllables and adaptors were /r/-/l/CVs and VCs, which do not produce cancelling formant patterns across syllabic position. In Experiment 2, /b/-/d/ continua were used in a paired-contrast procedure, believed to be sensitive to phonetic, but not acoustic, identity. In Experiment 3, cross-ear adaptation, also believed to tap phonetic rather than acoustic processes, was used. All three experiments refuted the cancellation hypothesis. Instead, it appears that the perceptual process treats syllable-initial consonants and syllable-final ones as inherently different. These results provide support for the use of demisyllabic representations in speech perception.     

Evidence for a central representation of instrument timbre

An information processing account of perception seeks to delineate the stages of processing through which a stimulus passes and determine the properties of the representation at each stage. Research in phonetic perception has identified two stages, the second of which is thought to encode abstract acoustic attributes of sounds. The present study provided a further test of this proposal by assessing whether nonphonetic stimuli could yield results similar to those obtained with phonetic stimuli. Five selective adaptation experiments were carried out with a trumpet—piano timbre continuum. Two manipulations were used to measure abstract encoding: cross-ear presentation of adaptor and test series, and the use of adaptors that were acoustically different from the continuum endpoints. The results provide evidence for an abstract representation of timbre. The similarity of the findings to those in the phonetic adaptation literature is discussed.     

Simple and contingent adaptation effects for place of articulation in stop consonants

Experiments on selective adaptation have shown that the locus of the phonetic category boundary between two segments shifts after repetitive listening to an adapting stimulus. Theoretical interpretations of these results have proposed that adaptation occurs either entirely at an auditory level of processing or at both auditory and more abstract phonetic levels. The present experiment employed two alternating stimuli as adaptors in an attempt to distinguish between these two possible explanations. Two alternating stimuli were used as adaptors in order to test for the presence of contingent effects and to compare these results to simple adaptation using only a single adaptor. Two synthetic CV series with different vowels that varied the place of articulation of the consonant were employed. When two alternating adaptors were used, contingent adaptation effects were observed for the two stimulus series. The direction of the shifts in each series was governed by the vowel context of the adapting syllables. Using the single adaptor data, a comparison was made between the additive effects of the single adaptors and their combined effects when presented in alternating pairs. With voiced adaptors, only within-series adaptation effects were found, and these data were consistent with a on,level model of selective adaptation. However, for the voiceless adaptors, both within- and cross-series adaptation effects were found, suggesting the possible presence of two levels of adaptation to place of articulation. Further, the contingent adaptation effects with the voiceless adaptors seemed to be the result of the additive effects of the two alternating adaptors. This result indicates that previously reported contingent adaptation results may also reflect the net vowel specific adaptation effects after cancellation of other, nonvowel dependent effects and that caution is needed in interpreting such results.     

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.     

Linguistic relativism and selective adaptation for speech: A comparative study of English and Thai

The effect of repeated exposure to prevoiced and voiced stimuli on the voiced/voiceless category boundary was compared for monolingual native English speakers and bilingual native speakers of Thai. The English speakers, for whom the two adaptors were members of the same phoneme class, showed equivalent shifts towards the adapting stimulus under both conditions. The Thai subjects, who perceived the two adaptors as belonging to two distinct phoneme classes, showed a shift of the voiced/voiceless boundary only for the voiced adaptation condition; exposure to the prevoiced adaptor had no effect.     

Susceptibility of a stop consonant to adaptation on a speech-nonspeech continuum: Further evidence against feature detectors in speech perception

The present experiment uses the perceptual adaptation paradigm to establish the validity of a previous test of the feature detector model of speech perception. In the present study, a synthetic stimulus series varied from a CV syllable, [ba], to a nonspeech buzz. When the endpoint tokens were employed alternatively as adaptors, the category boundary was shifted relative to unadapted identification in each adaptor condition. This result suggests that a prior test which used a vowel as the speech endpoint was legitimate because a stop consonant, an exemplary speech sound, was also susceptible to perceptual adaptation in a speech-nonspeech context. Feature detector models predict, incorrectly, that this outcome is impossible. Therefore, this finding may be taken to undermine the interpretation of adaptation as fatigue in a set of detectors tuned to detect the distinctive features of linguistic analysis.     

Temporary ambiguity in whispered word recognition: a semantic priming study

We examined whether listeners use acoustic correlates of voicing to resolve lexical ambiguities created by whispered speech in which a key feature, the voicing, is missing. Three associative priming experiments were conducted. The results showed a priming effect with whispered primes that included an intervocalic voiceless consonant (/petal/ “petal”) when the visual targets (FLEUR “flower”) were presented at the offset of the primes. A priming effect emerged with whispered primes that included a voiced intervocalic consonant (/pedal/ “pedal”) when the delay between the offset of the primes and the visual targets (VELO “bike”) was increased by 50 ms. In none of the experiments, the voiced primes (/pedal/) facilitated the processing of the targets (FLEUR) associated with the voiceless primes (/petal/). Our results suggest that the acoustic correlates of voicing are used by listeners to recover the intended words. Nonetheless, the retrieval of the voiced feature is not immediate during whispered word recognition.     

Adaptation is automatic

Two experiments were used to test whether selective adaptation for speech occurs automatically or instead requires attentional resources. A control condition demonstrated the usual large identification shifts caused by repeatedly presenting an adapting sound (/wa/, with listeners identifying members of a /ba/-/wa/ test series). Two types of distractor tasks were used: (1) Subjects did a rapid series of arithmetic problems during the adaptation periods (Experiments 1 and 2), or (2) they made a series of rhyming judgments, requiring phonetic coding (Experiment 2). A control experiment (Experiment 3) demonstrated that these tasks normally impose a heavy attentional cost on phonetic processing. Despite this, for both experimental conditions, the observed adaptation effect was just as large as in the control condition. This result indicates that adaptation is automatic, operating at an early, preattentive level. The implications of these results for current models of speech perception are discussed.     

Contingent feature analysis in speech perception

A contingent adaptation effect is reported for speech perception. Experiments were conducted to test the effects of an alternating sequence of two adapting syllables, [da] and [t^hi], on the perception of two series of synthetic speech syllables, [ba]-[p^ha] and [bi]-[p^hi]. Each of the test series consisted of 11 stimuli varying in voice onset time, a cue which distinguishes voiced from voiceless stop consonants in word-initial position. The [da]-[t^hi] adapting sequence produced opposite shifts in the loci of the phonetic boundaries for the two test series. For the [ba]-[p^ha] series, listeners made fewer identification responses to the [b] category after adaptation, while for the [bi]-[p^hi] series, listeners made more responses to the [b] category. The opposing shifts indicate that the perceptual analysis of voicing in stop consonants is carried out with respect to vowel environment.     

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.     

Comparison of consonantal and vocalic cues in selective adaptation

The acoustic cues to the phonetic identity of diphthongs normally include both spectral quality and dynamic change. This fact was exploited in a series of selective adaptation experiments examining the possibility of mutual adaptive effects between these two types of acoustic cues. One continuum of syllables varying from [εi] to [εd] and another varying from [ε] to [εi] were synthesized; endpoint stimuli of both series used as adaptors caused identification boundaries to be shifted. Cross-series adaptation was also attempted on the [ε?εi] stimuli, using [?], [∞], and [ai]. Only [ai] proved effective as an adaptor, suggesting the mediation of a rather abstract auditory level of similarity. The results argue strongly against interpretations in terms of feature detectors, but appear compatible with an “auditory contrast” explanation, which might in turn be incorporated within adaptation level theory in the form recently discussed by Restle (1978). The cross-series results further suggest that selective adaptation might be used to quantify the perceptual distance between auditory cues in speech.     

特征关联的类别间面孔适应

研究通过系列实验探讨了面孔适应不仅仅发生在形状选择性上, 也能发生在任务相关的特征上有内在关联的两个不同类别的物体间。实验1以带有明显性别倾向的物品图片作为适应刺激, 让被试对男女之间morphing程度不同的图片面孔进行性别辨别, 考察了不同适应刺激呈现时间的类别间面孔适应。结果表明适应刺激呈现时间大于50 ms时均存在类别间面孔适应效应。实验2评估了“性别”这一特征以及适应刺激形式在类别间面孔适应中所起的作用, 结果发现带有性别倾向的物品图片、相应的物品名称和性别文字(“男性”、“女性”) 3种适应刺激类型均能产生类别间适应。实验3通过操纵适应刺激上的注意负荷(高负荷、低负荷和无负荷), 探究了注意对类别间面孔适应的影响。结果表明随着注意负荷的增加, 类别间面孔适应效应减小。3个实验报告了一个新异的类别间适应后效, 证明了适应也能发生于在任务相关特征上有内在关联的两个不同类别的物体间。     

Vowel-contingent feature detection

Do vowel-contingent selective adaptation effects for place of articulation depend on vowel identity, or on the particular formant frequencies used? An experiment is reported here which tested the adaptation effects of consonants with exactly the same formant transitions before different diphthongs. In this experiment, the phonetic identity of the vowel and the formant frequencies of the consonant are not confounded as they have been in previous studies. In the contingent adaptation condition, no phoneme boundary shifts were observed, and this is interpreted along with previous evidencefor such phoneme boundary shifts when phonetic identity of the vowel and formant frequencies are confounded as indicating that adaptation operates on the spectral representation of the stimulus. Other evidence consistent with this conclusion is that adaptation with alternating adaptors from each end of the test series produced negligible shifts, and that a single adaptor from a diphthong series different from that of the test series produced phoneme boundary shifts as large as those with a single adaptor from the same test series.     

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.     

Reaction time for voiced and whispered /a/ in stutterers and nonstutterers

Recent research reviewed in this article suggests that stutterers' inability to initiate phonation promptly could be a significant factor in the occurence of stuttering. Since stuttering is either completely absent or markedly reduced in frequency during whisper, the present study tested the hypothesis that stutterers do not significantly differ from nonstutterers in reaction time (RT) for the initiation of whispered/a/, whereas the two groups differ significantly in RT for the initiation of voiced /a/. Ten adult stutterers and an equal number of comparable nonstutterers produced prolonged versions of the vowel /a/ using voice and whisper in response to tone stimuli. The results showed that stutteres and nonstutterers did not differ in RT for either voiced or whispered /a/. The stutterers, however, exhibited significantly longer RT to produce voiced /a/ than whispered /a/.     

Adaptation of the relative onset time of two-component tones

The results of three selective adaptation experiments employing nonspeech signals that differed in temporal onset are reported. In one experiment, adaptation effects were observed when both the adapting and test stimuli were selected from the same nonspeech test continuum. This result was interpreted as evidence for selective processing of temporal order information in nonspeech signals. Two additional experiments tested for the presence of cross-series adaptation effects from speech to nonspeech and then from nonspeech to speech. Both experiments failed to show any evidence of cross-series adaptation effects, implying a possible dissociation between perceptual classes of speech and nonspeech signals in processing temporal order information. Despite the absence of cross-series effects, it is argued that the ability of the auditory system to process temporal order information may still provide a possible basis for explaining the perception of voicing in stops that differ in VOT. The results of the present experiments, taken together with earlier findings on the perception of temporal onset in nonspeech signals, were viewed as an example of the way spoken language has exploited the basic sensory capabilities of the auditory system to signal phonetic differences.     

Selective adaptation effects on end-point stimuli in a speech series

Recent experiments in speech perception using the selective adaptation paradigm have found that the phonetic boundary of a test series shifts following adaptation. However, no changes within the phonetic category have been found. In the present experiment, a series of voiced CV syllables which varied along the feature of place was used in a selective adaptation paradigm. The end-point stimuli trom the test series were used as adaptors. Subjects used a 6-point rating scale to respond to the stimuli instead of the usual two-category identification. The average rating for end-point stimuli from the same category as the adaptor, as well as the boundary stimuli, shifted as a function of adaptation. In all cases, the average rating response shifted toward that of the unadapted category. The average rating for stimuli in the opposite category from that of the adaptor remained relatively unchanged. These results indicate that the entire category of the adapting stimulus changes as a function of selective adaptation and that the effect is not confined to stimuli near the phonetic boundary.     

Are selective adaptation and contrast effects really distinct?

Although there is evidence that selective adaptation and contrast effects in speech perception are produced by the same mechanisms, Sawusch and Jusczyk (1981) reported a dissociation between the effects and concluded that adaptation and contrast occur at separate processing levels. They found that an ambiguous test stimulus was more likely to be labeled b following adaptation with [pha] and more likely to be labeled p following adaptation with [ba] or [spa] (the latter consisting of [ba] preceded by [s] noise). In the contrast session, where a single context stimulus occurred with a single test item, the [ba] and [pha] contexts had contrastive effects similar to those of the [ba] and [pha] adaptors, but the [spa] context produced an increase in b responses to the test stimulus, an effect opposite to that of the [spa] adaptor. One interpretation of this difference is that the rapid presentation of the [spa] adaptor gave rise to "streaming," whereby the [s] was perceptually segregated from the [ba]. In our experiment, we essentially replicated the results of Sawusch and Jusczyk (1981), using procedures similar to theirs. Next, we increased the interadaptor interval to remove the likelihood of stream segregation and found that the adaptation and contrast effects converged.