Perceptual narrowing in speech and face recognition : evidence for intra-individual cross-domain relations

During the first year of life, infants undergo perceptual narrowing in the domains of speech and face perception. This is typically characterized by improvements in infants' abilities in discriminating among stimuli of familiar types, such as native speech tones and same-race faces. Simultaneously, infants begin to decline in their ability to discriminate among stimuli of types with which they have little experience, such as non-native tones and other-race faces. The similarity in time-frames during which perceptual narrowing seems to occur in the domains of speech and face perception has led some researchers to hypothesize that the perceptual narrowing in these domains could be driven by shared domain-general processes. To explore this hypothesis, we tested 53 Caucasian 9-month-old infants from monolingual German households on their ability to discriminate among non-native Cantonese speech tones, as well among same-race German faces and other-race Chinese faces. We tested the infants using an infant-controlled habituation-dishabituation paradigm, with infants' preferences for looking at novel stimuli versus the habituated stimuli (dishabituation scores) acting as indicators of discrimination ability. As expected for their age, infants were able to discriminate between same-race faces, but not between other-race faces or non-native speech tones. Most interestingly, we found that infants' dishabituation scores for the non-native speech tones and other-race faces showed significant positive correlations, while the dishabituation scores for non-native speech tones and same-race faces did not. These results therefore support the hypothesis that shared domain-general mechanisms may drive perceptual narrowing in the domains of speech and face perception

Perceptual narrowing in speech and face recognition : evidence for intra-individual cross-domain relations

During the first year of life, infants undergo perceptual narrowing in the domains of speech and face perception. This is typically characterized by improvements in infants' abilities in discriminating among stimuli of familiar types, such as native speech tones and same-race faces. Simultaneously, infants begin to decline in their ability to discriminate among stimuli of types with which they have little experience, such as non-native tones and other-race faces. The similarity in time-frames during which perceptual narrowing seems to occur in the domains of speech and face perception has led some researchers to hypothesize that the perceptual narrowing in these domains could be driven by shared domain-general processes. To explore this hypothesis, we tested 53 Caucasian 9-month-old infants from monolingual German households on their ability to discriminate among non-native Cantonese speech tones, as well among same-race German faces and other-race Chinese faces. We tested the infants using an infant-controlled habituation-dishabituation paradigm, with infants' preferences for looking at novel stimuli versus the habituated stimuli (dishabituation scores) acting as indicators of discrimination ability. As expected for their age, infants were able to discriminate between same-race faces, but not between other-race faces or non-native speech tones. Most interestingly, we found that infants' dishabituation scores for the non-native speech tones and other-race faces showed significant positive correlations, while the dishabituation scores for non-native speech tones and same-race faces did not. These results therefore support the hypothesis that shared domain-general mechanisms may drive perceptual narrowing in the domains of speech and face perception

How tone, intonation and emotion shape the development of infants' fundamental frequency perception

Fundamental frequency (ƒ0), perceived as pitch, is the first and arguably most salient auditory component humans are exposed to since the beginning of life. It carries multiple linguistic (e.g., word meaning) and paralinguistic (e.g., speakers’ emotion) functions in speech and communication. The mappings between these functions and ƒ0 features vary within a language and differ cross-linguistically. For instance, a rising pitch can be perceived as a question in English but a lexical tone in Mandarin. Such variations mean that infants must learn the specific mappings based on their respective linguistic and social environments. To date, canonical theoretical frameworks and most empirical studies do not view or consider the multi-functionality of ƒ0, but typically focus on individual functions. More importantly, despite the eventual mastery of ƒ0 in communication, it is unclear how infants learn to decompose and recognize these overlapping functions carried by ƒ0. In this paper, we review the symbioses and synergies of the lexical, intonational, and emotional functions that can be carried by ƒ0 and are being acquired throughout infancy. On the basis of our review, we put forward the Learnability Hypothesis that infants decompose and acquire multiple ƒ0 functions through native/environmental experiences. Under this hypothesis, we propose representative cases such as the synergy scenario, where infants use visual cues to disambiguate and decompose the different ƒ0 functions. Further, viable ways to test the scenarios derived from this hypothesis are suggested across auditory and visual modalities. Discovering how infants learn to master the diverse functions carried by ƒ0 can increase our understanding of linguistic systems, auditory processing and communication functions

Perceptual reorganization of lexical tones : effects of age and experimental procedure

Findings on the perceptual reorganization of lexical tones are mixed. Some studies report good tone discrimination abilities for all tested age groups, others report decreased or enhanced discrimination with increasing age, and still others report U-shaped developmental curves. Since prior studies have used a wide range of contrasts and experimental procedures, it is unclear how specific task requirements interact with discrimination abilities at different ages. In the present work, we tested German and Cantonese adults on their discrimination of Cantonese lexical tones, as well as German-learning infants between 6 and 18 months of age on their discrimination of two specific Cantonese tones using two different types of experimental procedures. The adult experiment showed that German native speakers can discriminate between lexical tones, but native Cantonese speakers show significantly better performance. The results from German-learning infants suggest that 6-and 18-month-olds discriminate tones, while 9-month-olds do not, supporting a U-shaped developmental curve. Furthermore, our results revealed an effect of methodology, with good discrimination performance at 6 months after habituation but not after familiarization. These results support three main conclusions. First, habituation can be a more sensitive procedure for measuring infants' discrimination than familiarization. Second, the previous finding of a U-shaped curve in the discrimination of lexical tones is further supported. Third, discrimination abilities at 18 months appear to reflect mature perceptual sensitivity to lexical tones, since German adults also discriminated the lexical tones with high accuracy

Perceptual narrowing in face- and speech-perception domains in infancy : a longitudinal approach

During the first year of life, infants undergo a process known as perceptual narrowing, which reduces their sensitivity to classes of stimuli which the infants do not encounter in their environment. It has been proposed that perceptual narrowing for faces and speech may be driven by shared domain-general processes. To investigate this theory, our study longitudinally tested 50 German Caucasian infants with respect to these domains first at 6 months of age followed by a second testing at 9 months of age. We used an infant-controlled habituation-dishabituation paradigm to test the infants’ ability to discriminate among other-race Asian faces and non-native Cantonese speech tones, as well as same-race Caucasian faces as a control. We found that while at 6 months of age infants could discriminate among all stimuli, by 9 months of age they could no longer discriminate among other-race faces or non-native tones. However, infants could discriminate among same-race stimuli both at 6 and at 9 months of age. These results demonstrate that the same infants undergo perceptual narrowing for both other-race faces and non-native speech tones between the ages of 6 and 9 months. This parallel development of perceptual narrowing occurring in both the face and speech perception modalities over the same period of time lends support to the domain-general theory of perceptual narrowing in face and speech perception

Bimodal familiarization re-sensitizes 12-month-old infants to other-race faces

Perceptual narrowing in the domain of face perception typically begins to reduce infants’ sensitivity to differences distinguishing other-race faces from approximately 6 months of age. The present study investigated whether it is possible to re-sensitize Caucasian 12-month-old infants to other-race Asian faces through statistical learning by familiarizing them with different statistical distributions of these faces. The familiarization faces were created by generating a morphed continuum from one Asian face identity to another. In the unimodal condition, infants were familiarized with a frequency distribution wherein they saw the midpoint face of the morphed continuum the most frequently. In the bimodal condition, infants were familiarized with a frequency distribution wherein they saw faces closer to the endpoints of the morphed continuum the most frequently. After familiarization, infants were tested on their discrimination of the two original Asian faces. The infants’ looking times during the test indicated that infants in the bimodal condition could discriminate between the two faces, while infants in the unimodal condition could not. These findings therefore suggest that 12-month-old Caucasian infants could be re-sensitized to Asian faces by familiarizing them with a bimodal frequency distribution of such faces

Does musicality assist foreign language learning? : perception and production of Thai vowels, consonants and lexical tones by musicians and non-musicians

The music and spoken language domains share acoustic properties such as fundamental frequency (f0, perceived as pitch), duration, resonance frequencies, and intensity. In speech, the acoustic properties form an essential part in differentiating between consonants, vowels, and lexical tones. This study investigated whether there is any advantage of musicality in the perception and production of Thai speech sounds. Two groups of English-speaking adults—one comprising formally trained musicians and the other non-musicians—were tested for their perception and production of Thai consonants, vowels, and tones. For both groups, the perception and production accuracy scores were higher for vowels than consonants and tones, and in production, there was also better accuracy for tones than consonants. Between the groups, musicians (defined as having more than five years of formal musical training) outperformed non-musicians (defined as having less than two years of formal musical training) in both the perception and production of all three sound types. Additional experiential factors that positively influenced the accuracy rates were the current hours of practice per week and those with some indication of an augmentation due to musical aptitude, but only in perception. These results suggest that music training, defined as formal training for more than five years, and musical training, expressed in hours of weekly practice, facilitate the perception and production of non-native speech sounds

[In Press] The development of tone discrimination in infancy : evidence from a cross-linguistic, multi-lab report

We report the findings of a multi-language and multi-lab investigation of young infants’ ability to discriminate lexical tones as a function of their native language, age and language experience, as well as of tone properties. Given the high prevalence of lexical tones across human languages, understanding lexical tone acquisition is fundamental for comprehensive theories of language learning. While there are some similarities between the developmental course of lexical tone perception and that of vowels and consonants, findings for lexical tones tend to vary greatly across different laboratories. To reconcile these differences and to assess the developmental trajectory of native and non-native perception of tone contrasts, this study employed a single experimental paradigm with the same two pairs of Cantonese tone contrasts (perceptually similar vs. distinct) across 13 laboratories in Asia-Pacific, Europe and North-America testing 5-, 10- and 17-month-old monolingual (tone, pitch-accent, non-tone) and bilingual (tone/non-tone, non-tone/non-tone) infants. Across the age range and language backgrounds, infants who were not exposed to Cantonese showed robust discrimination of the two non-native lexical tone contrasts. Contrary to this overall finding, the statistical model assessing native discrimination by Cantonese-learning infants failed to yield significant effects. These findings indicate that lexical tone sensitivity is maintained from 5 to 17 months in infants acquiring tone and non-tone languages, challenging the generalisability of the existing theoretical accounts of perceptual narrowing in the first months of life. RESEARCH HIGHLIGHTS: This is a multi-language and multi-lab investigation of young infants’ ability to discriminate lexical tones. This study included data from 13 laboratories testing 5-, 10-, and 17-month-old monolingual (tone, pitch-accent, non-tone) and bilingual (tone/non-tone, non-tone/non-tone) infants. Overall, infants discriminated a perceptually similar and a distinct non-native tone contrast, although there was no evidence of a native tone-language advantage in discrimination. These results demonstrate maintenance of tone discrimination throughout development