Human adults and human infants show a "perceptual magnet effect" for the prototypes of speech categories, monkeys do not

Many perceptual categories exhibit internal structure in which category prototypes play an important role. In the four experiments reported here, the internal structure of phonetic categories was explored in studies involving adults, infants, and monkeys. In Experiment 1, adults rated the category goodness of 64 variants of the vowel i parallel on a scale from 1 to 7. The results showed that there was a certain location in vowel space where listeners rated the i parallel vowels as best instances, or prototypes. The perceived goodness of i parallel vowels declined systematically as stimuli were further removed from the prototypic i parallel vowel. Experiment 2 went beyond this initial demonstration and examined the effect of speech prototypes on perception. Either the prototypic or a nonprototypic i parallel vowels was used as the referent stimulus and adults' generalization to other members of the category was examined. Results showed that the typicality of the speech stimulus strongly affected perception. When the prototype of the category served as the referent vowel, there was significantly greater generalization to other i parallel vowels, relative to the situation in which the nonprototype served as the referent. The notion of a perceptual magnet was introduced. The prototype of the category functioned like a perceptual magnet for other category members; it assimilated neighboring stimuli, effectively pulling them toward the prototype. In Experiment 3, the ontogenetic origins of the perceptual magnet effect were explored by testing 6-month-old infants. The results showed that infants' perception of vowels was also strongly affected by speech prototypes. Infants showed significantly greater generalization when the prototype of the vowel category served as the referent; moreover, their responses were highly correlated with those of adults. In Experiment 4, Rhesus monkeys were tested to examine whether or not the prototype's magnet effect was unique to humans. The animals did not provide any evidence of speech prototypes; they did not exhibit the magnet effect. It is suggested that the internal organization of phonetic categories around prototypic members is an ontogenetically early, species-specific, aspect of the speech code.     

Human adults and human infants show a “perceptual magnet effect” for the prototypes of speech categories,monkeys do not

Many perceptual categories exhibit internal structure in which category prototypes play an important role. In the four experiments reported here, the internal structure of phonetic categories was explored in studies involving adults, infants, and monkeys. In Experiment 1, adults rated the category goodness of 64 variants of the vowel /i/ on a scale from 1 to 7. The results showed that there was a certain location in vowel space where listeners rated the /i/ vowels as best instances, or prototypes. The perceived goodness of Iii vowels declined systematically as stimuli were further removed from the prototypic Iii vowel. Experiment 2 went beyond this initial demonstration and examined the effect of speech prototypes on perception. Either the prototypic or a nonprototypic IM vowel was used as the referent stimulus and adults’ generalization to other members of the category was examined. Results showed that the typicality of the speech stimulus strongly affected perception. When the prototype of the category served as the referent vowel, there was significantly greater generalization to other /i/ vowels, relative to the situation in which the nonprototype served as the referent. The notion of aperceptual magnet was introduced. The prototype of the category functioned like a perceptual magnet for other category members; it assimilated neighboring stimuli, effectively pulling them toward the prototype. In Experiment 3, the ontogenetic origins of the perceptual magnet effect were explored by testing 6-month-old infants. The results showed that infants’ perception of vowels was also strongly affected by speech prototypes. Infants showed significantly greater generalization when the prototype of the vowel category served as the referent; moreover, their responses were highly correlated with those of adults. In Experiment 4, Rhesus monkeys were tested to examine whether or not the prototype’s magnet effect was unique to humans. The animals did not provide any evidence of speech prototypes; they did not exhibit the magnet effect. It is suggested that the internal organization of phonetic categories around prototypic members is an ontogenetically early, species-specific, aspect of the speech code     

The shift in infant preferences for vowel duration and pitch contour between 6 and 10 months of age

This study investigates the influence of the acoustic properties of vowels on 6‐ and 10‐month‐old infants’ speech preferences. The shape of the contour (bell or monotonic) and the duration (normal or stretched) of vowels were manipulated in words containing the vowels /i/ and /u/, and presented to infants using a two‐choice preference procedure. Experiment 1 examined contour shape: infants heard either normal‐duration bell‐shaped and monotonic contours, or the same two contours with stretched duration. The results show that 6‐month‐olds preferred bell to monotonic contours, whereas 10‐month‐olds preferred monotonic to bell contours. In Experiment 2, infants heard either normal‐duration and stretched bell contours, or normal‐duration and stretched monotonic contours. As in Experiment 1, infants showed age‐specific preferences, with 6‐month‐olds preferring stretched vowels, and 10‐month‐olds preferring normal‐duration vowels. Infants’ attention to the acoustic qualities of vowels, and to speech in general, undergoes a dramatic transformation in the final months of the first year, a transformation that aligns with the emergence of other developmental milestones in speech perception.     

Influence of vocalic context on perception of the [∫]-[s] distinction

When synthetic fricative noises from a [∫]-[s] continuum are followed by [a] or [u] (with appropriate formant transitions), listeners perceive more instances of [s] in the context of [u] than in the context of [a]. Presumably, this reflects a perceptual adjustment for the coarticulatory effect of rounded vowels on preceding fricatives. In Experiment 1, we found that varying the duration of the fricative noise leaves the perceptual context effect unchanged, whereas insertion of a silent interval following the noise reduces the effect substantially. Experiment 2 suggested that it is temporal separation rather than the perception of an intervening stop consonant that is responsible for this reduction, in agreement with recent, analogous observations on anticipatory coarticulation. In Experiment 3, we showed that the vowel context effect disappears when the periodic stimulus portion is synthesized so as to contain no formant transitions. To dissociate the contribution of formant transitions from contextual effects due to vowel quality per se, Experiment 4 employed synthetic fricative noises followed by periodic portions excerpted from naturally produced [∫a], [sa], [∫u], and [su]. The results showed strong and largely independent effects of formant transitions and vowel quality on fricative perception. In addition, we found a strong speaker (male vs. female) normalization effect. All three influences on fricative perception were reduced by temporal separation of noise and periodic stimulus portions. Although no single hypothesis can explain all of our results, they are generally supportive of the view that some knowledge of the dynamics of speech production has a role in speech perception.     

Converging sources of evidence on spoken and perceived rhythms of speech: cyclic production of vowels in monosyllabic stress feet

The article reviews the literature from psychology, phonetics, and phonology bearing on production and perception of syllable timing in speech. A review of the psychological and phonetics literature suggests that production of vowels and consonants are interleaved in syllable sequences in such a way that vowel production is continuous or nearly so. Based on that literature, a hypothesis is developed concerning the perception of syllable timing assuming that vowel production is continuous. The hypothesis is that perceived syllable timing corresponds to the times sequencing of the vowels as produced and not to the timing either of vowel onsets as conventionally measured or of syllable-initial consonants. Three experiments support the hypothesis. One shows that information present during the portion of an acoustic signal in which a syllable-initial consonant predominates is used by listeners to identify the vowel. Compatibly, this information for the vowel contributes to the vowel's perceived duration. Finally, a measure of the perceived timing of a syllable correlates significantly with the time required to identify syllable-medial vowels but not with time to identify the syllable-initial consonants. Further support for the proposed mode of vowel-consonant production and perception is derived from the literature on phonology. Language-specific phonological conventions can be identified that may reflect exaggerations and conventionalizations of the articulatory tendency for vowels to be produced continuously in speech.     

Effects of stimulus response compatibility on covert imitation of vowels

When we observe someone else speaking, we tend to automatically activate the corresponding speech motor patterns. When listening, we therefore covertly imitate the observed speech. Simulation theories of speech perception propose that covert imitation of speech motor patterns supports speech perception. Covert imitation of speech has been studied with interference paradigms, including the stimulus–response compatibility paradigm (SRC). The SRC paradigm measures covert imitation by comparing articulation of a prompt following exposure to a distracter. Responses tend to be faster for congruent than for incongruent distracters; thus, showing evidence of covert imitation. Simulation accounts propose a key role for covert imitation in speech perception. However, covert imitation has thus far only been demonstrated for a select class of speech sounds, namely consonants, and it is unclear whether covert imitation extends to vowels. We aimed to demonstrate that covert imitation effects as measured with the SRC paradigm extend to vowels, in two experiments. We examined whether covert imitation occurs for vowels in a consonant–vowel–consonant context in visual, audio, and audiovisual modalities. We presented the prompt at four time points to examine how covert imitation varied over the distracter’s duration. The results of both experiments clearly demonstrated covert imitation effects for vowels, thus supporting simulation theories of speech perception. Covert imitation was not affected by stimulus modality and was maximal for later time points.

     

Suprasegmental information affects processing of talking faces at birth

From birth, newborns show a preference for faces talking a native language compared to silent faces. The present study addresses two questions that remained unanswered by previous research: (a) Does the familiarity with the language play a role in this process and (b) Are all the linguistic and paralinguistic cues necessary in this case? Experiment 1 extended newborns’ preference for native speakers to non-native ones. Given that fetuses and newborns are sensitive to the prosodic characteristics of speech, Experiments 2 and 3 presented faces talking native and nonnative languages with the speech stream being low-pass filtered. Results showed that newborns preferred looking at a person who talked to them even when only the prosodic cues were provided for both languages. Nonetheless, a familiarity preference for the previously talking face is observed in the “normal speech” condition (i.e., Experiment 1) and a novelty preference in the “filtered speech” condition (Experiments 2 and 3). This asymmetry reveals that newborns process these two types of stimuli differently and that they may already be sensitive to a mismatch between the articulatory movements of the face and the corresponding speech sounds.     

The quest for generalizations over consonants: Asymmetries between consonants and vowels are not the by-product of acoustic differences

Consonants and vowels may play different roles during language processing, consonants being preferentially involved in lexical processing, and vowels tending to mark syntactic constituency through prosodic cues. In support of this view, artificial language learning studies have demonstrated that consonants (C) support statistical computations, whereas vowels (V) allow certain structural generalizations. Nevertheless, these asymmetries could be mere by-products of lower level acoustic differences between Cs and Vs, in particular the energy they carry, and thus their relative salience. Here we address this issue and show that vowels remain the preferred targets for generalizations, even when consonants are made highly salient or vowels barely audible. Participants listened to speech streams of nonsense CVCVCV words, in which consonants followed a simple ABA structure. Participants failed to generalize this structure over sonorant consonants (Experiment 1), even when vowel duration was reduced to one third of that of consonants (Experiment 2). When vowels were eliminated from the stream, participants showed only a marginal evidence of generalizations (Experiment 4). In contrast, participants readily generalized the structure over barely audible vowels (Experiment 3). These results show that different roles of consonants and vowels cannot be readily reduced to acoustical and perceptual differences between these phonetic categories.     

When infants talk,infants listen: pre‐babbling infants prefer listening to speech with infant vocal properties

To learn to produce speech, infants must effectively monitor and assess their own speech output. Yet very little is known about how infants perceive speech produced by an infant, which has higher voice pitch and formant frequencies compared to adult or child speech. Here, we tested whether pre‐babbling infants (at 4–6 months) prefer listening to vowel sounds with infant vocal properties over vowel sounds with adult vocal properties. A listening preference favoring infant vowels may derive from their higher voice pitch, which has been shown to attract infant attention in infant‐directed speech (IDS). In addition, infants' nascent articulatory abilities may induce a bias favoring infant speech given that 4‐ to 6‐month‐olds are beginning to produce vowel sounds. We created infant and adult /i/ (‘ee’) vowels using a production‐based synthesizer that simulates the act of speaking in talkers at different ages and then tested infants across four experiments using a sequential preferential listening task. The findings provide the first evidence that infants preferentially attend to vowel sounds with infant voice pitch and/or formants over vowel sounds with no infant‐like vocal properties, supporting the view that infants' production abilities influence how they process infant speech. The findings with respect to voice pitch also reveal parallels between IDS and infant speech, raising new questions about the role of this speech register in infant development. Research exploring the underpinnings and impact of this perceptual bias can expand our understanding of infant language development.     

Infant Directed Speech in Natural Interaction—Norwegian Vowel Quantity and Quality

An interactive face-to-face setting is used to study natural infant directed speech (IDS) compared to adult directed speech (ADS). With distinctive vowel quantity and vowel quality, Norwegian IDS was used in a natural quasi-experimental design. Six Norwegian mothers were recorded over a period of 6 months alone with their infants and in an adult conversation. Vowel duration and spectral attributes of the vowels /a:/, /i:/ and /u:/, and their short counterparts /a/ /i/ and /u/ were analysed. Repeated measures analyses show that effects of vowel quantity did not differ between ADS and IDS, and for back vowel qualities, the vowel space was shifted upwards in IDS compared to ADS suggesting that fronted articulations in natural IDS may visually enhance speech to infants.     

Pattern preferences at birth and their interaction with habituation-induced novelty preferences

Three experiments are described which relate to models of infant visual preferences, and to the ways in which preferences can be modified or created by habituation. In all experiments newborn babies were used as subjects. In Experiments equated 1 and 2 infants were presented with pairs of stimuli that were equated for contour density but which differed in spatial frequency components. The preferences obtained give support to Banks and Salapatek's (1981, Journal of Experimental Child Psychology, 31, 1-45) model of infant preferences which predicts that the maximally preferred stimulus will be that which contains high amplitude spatial frequency components falling within the age group's peak contrast sensitivity. In Experiment 3 an infant-controlled habituation procedure was used. The results obtained suggest that strong natural preferences based on the infants' peak contrast sensitivity cannot be changed by habituating infants either to the preferred or to the nonpreferred member of a stimulus pair. However, where no prior preference exists between two stimuli that are perceptually highly discriminable, very strong novelty preferences are found after habituating newborns to either stimulus. The results suggest that the contrast sensitivity model can be a powerful predictor of preferential looking in newborns, and in addition are further evidence that preferences based on experience can be found from birth.     

The role of kinetic information in newborns' perception of illusory contours

Previous research, in which static figures were used, showed that the ability to perceive illusory contours emerges around 7 months of age. However, recently, evidence has suggested that 2-3-month-old infants are able to perceive illusory contours when motion information is available (Johnson & Mason, 2002; Otsuka & Yamaguchi, 2003). The present study was aimed at investigating whether even newborns might perceive kinetic illusory contours when a motion easily detected by the immature newborn's visual system (i.e. stroboscopic motion) is used. In Experiment 1, using a preference looking technique, newborns' perception of kinetic illusory contours was explored using a Kanizsa figure in a static and in a kinetic display. The results showed that newborns manifest a preference for the illusory contours only in the kinetic, but not in the static, condition. In Experiment 2, using an habituation technique, newborns were habituated to a moving shape that was matched with the background in terms of random-texture-surface; thus the recovery of the shape was possible relying only on kinetic information. The results showed that infants manifested a novelty preference when presented with luminance-defined familiar and novel shapes. Altogether these findings provide evidence that motion enhances (Experiment 1) and sometimes is sufficient (Experiment 2) to induce newborns' perception of illusory contours.     

The multidimensional nature of hyperspeech: Evidence from Japanese vowel devoicing

We investigate the hypothesis that infant-directed speech is a form of hyperspeech, optimized for intelligibility, by focusing on vowel devoicing in Japanese. Using a corpus of infant-directed and adult-directed Japanese, we show that speakers implement high vowel devoicing less often when speaking to infants than when speaking to adults, consistent with the hyperspeech hypothesis. The same speakers, however, increase vowel devoicing in careful, read speech, a speech style which might be expected to pattern similarly to infant-directed speech. We argue that both infant-directed and read speech can be considered listener-oriented speech styles—each is optimized for the specific needs of its intended listener. We further show that in non-high vowels, this trend is reversed: speakers devoice more often in infant-directed speech and less often in read speech, suggesting that devoicing in the two types of vowels is driven by separate mechanisms in Japanese.     

Syllable similarity: The effects of differences in vowels, consonants, and order

In five experiments with synthetic and natural speech syllables, a rating task we used to study the effects of differences in vowels, consonants, and segment order on judged syllable similarity. The results of Experiments I-IV support neither a purely phonemic model of speech representation, in which vowel, consonant, and order are represented independently, nor a purely syllabic model, in which the three factors are integrated. Instead, the data indicate that subjects compare representations in which adjacent vowel and consonant are independent of one another but are not independent of their positions in the syllable. Experiment V provided no support for the hypothesis that this position-sensitive coding is due to acoustic differences in formant transitions.     

Perception of temporal order in vowel sequences with and without formant transitions.

Temporal-order perception of phoneme segments in running speech is much superior to temporal-order perception in repeating vowel sequences. The more rapid rates possible in running speech may be due largely to the presence of formant transitions. In a series of five experiments we observed that many temporal-order misjudgements of repeating vowels can be explained in terms of auditory stream segregation, triggered for the most part by discontinuities in first-formant frequencies of adjacent vowels. Streaming, however, can be suppressed by formant transitions appropriate for the perception of stop consonants and by continuous transitions resembling those in coarticulated vowels. At rapid sequence rates, when the constraints of auditory streaming are removed, correct temporal-order identification is limited by linguistic transformations of vowels into other phoneme segments.     

Infant directed speech and the development of speech perception: Enhancing development or an unintended consequence?

Infant directed speech (IDS) is a speech register characterized by simpler sentences, a slower rate, and more variable prosody. Recent work has implicated it in more subtle aspects of language development. Kuhl et al. (1997) demonstrated that segmental cues for vowels are affected by IDS in a way that may enhance development: the average locations of the extreme “point” vowels (/a/, /i/ and /u/) are further apart in acoustic space. If infants learn speech categories, in part, from the statistical distributions of such cues, these changes may specifically enhance speech category learning. We revisited this by asking (1) if these findings extend to a new cue (Voice Onset Time, a cue for voicing); (2) whether they extend to the interior vowels which are much harder to learn and/or discriminate; and (3) whether these changes may be an unintended phonetic consequence of factors like speaking rate or prosodic changes associated with IDS. Eighteen caregivers were recorded reading a picture book including minimal pairs for voicing (e.g., beach/peach) and a variety of vowels to either an adult or their infant. Acoustic measurements suggested that VOT was different in IDS, but not in a way that necessarily supports better development, and that these changes are almost entirely due to slower rate of speech of IDS. Measurements of the vowel suggested that in addition to changes in the mean, there was also an increase in variance, and statistical modeling suggests that this may counteract the benefit of any expansion of the vowel space. As a whole this suggests that changes in segmental cues associated with IDS may be an unintended by-product of the slower rate of speech and different prosodic structure, and do not necessarily derive from a motivation to enhance development.     

Effect of consonant/vowel letter organisation on the syllable counting task: evidence from English

Recent studies in alphabetic writing systems have investigated whether the status of letters as consonants or vowels influences the perception and processing of written words. Here, we examined to what extent the organisation of consonants and vowels within words affects performance in a syllable counting task in English. Participants were asked to judge the number of syllables in written words that were matched for the number of spoken syllables but comprised either 1 orthographic vowel cluster less than the number of syllables (hiatus words, e.g., triumph) or as many vowel clusters as syllables (e.g., pudding). In 3 experiments, we found that readers were slower and less accurate on hiatus than control words, even when phonological complexity (Experiment 1), number of reduced vowels (Experiment 2), and number of letters (Experiment 3) were taken into account. Interestingly, for words with or without the same number of vowel clusters and syllables, participants’ errors were more likely to underestimate the number of syllables than to overestimate it. Results are discussed in a cross-linguistic perspective.     

声调在汉语音节感知中的作用

探讨超音段(如声调)与音段信息的共同作用机制, 对口语词汇识别研究具有重要的理论意义。有研究探讨了声调在口语词汇语义通达阶段的作用, 但在相对早期的音节感知阶段, 声调与声母、韵母的共同作用机制还缺乏系统的认识。本研究采用oddball实验范式, 通过两个行为实验考察了声调在汉语音节感知中的作用。实验1发现检测声调和声母变化的时间没有差异, 均比检测韵母变化的时间长, 表明在汉语音节感知中对声调的敏感性不及韵母。实验2发现声母和韵母的组合并没有明显优于对韵母的觉察, 但声调与声母或韵母的同时变化都促进了被试对偏差刺激的觉察, 表明声调通过与声母、韵母的结合来共同影响汉语音节的感知加工。研究结果在认知行为层面为声调在音节感知中的作用机制提供了直接的实验证据, 为进一步探讨超音段与音段信息共同作用的认知神经机制提供了基础。     

Auditory enhancement and the perception of concurrent vowels

Listeners identified both constituents of double vowels created by summing the waveforms of pairs of synthetic vowels with the same duration and fundamental frequency. Accuracy of identification was significantly above chance. Effects of introducing such double vowels by visual or acoustical precursor stimuli were examined. Precursors specified the identity of one of the two constituent vowels. Performance was scored as the accuracy with which the other vowel was identified. Visual precursors were standard English spellings of one member of the vowel pair; acoustical precursors were 1-sec segments of one member of the vowel pair. Neither visual precursors nor contralateral acoustical precursors improved performance over the condition with no precursor. Thus, knowledge of the identity of one of the constituents of a double vowel does not help listeners to identify the other constituent. A significant improvement in performance did occur with ipsilateral acoustical precursors, consistent with earlier demonstrations that frequency components which undergo changes in spectral amplitude achieve enhanced auditory prominence relative to unchanging components. This outcome demonstrates the joint but independent operation of auditory and perceptual processes underlying the ability of listeners to understand speech despite adversely peaked frequency responses in communication channels.