Patricia K. Kuhl

Early language acquisition: cracking the speech code

Infants learn language with remarkable speed, but how they do it remains a mystery. New data show that infants use computational strategies to detect the statistical and prosodic patterns in language input, and that this leads to the discovery of phonemes and words. Social interaction with another human being affects speech learning in a way that resembles communicative learning in songbirds. The brains commitment to the statistical and prosodic patterns that are experienced early in life might help to explain the long-standing puzzle of why infants are better language learners than adults. Successful learning by infants, as well as constraints on that learning, are changing theories of language acquisition.

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

Foreign-language experience in infancy: Effects of short-term exposure and social interaction on phonetic learning

Infants acquire language with remarkable speed, although little is known about the mechanisms that underlie the acquisition process. Studies of the phonetic units of language have shown that early in life, infants are capable of discerning differences among the phonetic units of all languages, including native- and foreign-language sounds. Between 6 and 12 mo of age, the ability to discriminate foreign-language phonetic units sharply declines. In two studies, we investigate the necessary and sufficient conditions for reversing this decline in foreign-language phonetic perception. In Experiment 1, 9-mo-old American infants were exposed to native Mandarin Chinese speakers in 12 laboratory sessions. A control group also participated in 12 language sessions but heard only English. Subsequent tests of Mandarin speech perception demonstrated that exposure to Mandarin reversed the decline seen in the English control group. In Experiment 2, infants were exposed to the same foreign-language speakers and materials via audiovisual or audio-only recordings. The results demonstrated that exposure to recorded Mandarin, without interpersonal interaction, had no effect. Between 9 and 10 mo of age, infants show phonetic learning from live, but not prerecorded, exposure to a foreign language, suggesting a learning process that does not require long-term listening and is enhanced by social interaction.

Acoustic Determinants of Infant Preference for Motherese Speech

Three experiments investigated possible acoustic determinants of the infant listening preference for motherese speech found by Fernald (1985). To test the hypothesis that the intonation of motherese speech was sufficient to elicit this preference, it was necessary to eliminate lexical content and to isolate the three maior acoustic correlates of intonation: (1) fundamental frequency (Fo), or pitch: (2) amplitude, correlated with loudness; and (3) duration, related to speech rhythm. Three sets of auditory reinforcers were computer-synthesized, derived from the FO (Experiment 1). amplitude (Experiment 2). and durotion (Experiment 3) characteristics of the infant- and adult-directed natural speech samples used by Fernald (1985). Thus, each of these experiments focused on particular prosodic variables in the absence of segmental variation. Twenty 4-month-old infants were tested in on operant ouditory preference procedure in each experiment. Infonts showed a significant preference for the FO-patterns of motherese speech, but not for the amplitude or duration patterns of motherese.

Foundations for a new science of learning

Dissecting Dyslexia and Learning Difficulties in learning to read, despite reasonable effort and instruction, form the basis of dyslexia. Gabrieli (p. 280; see the cover) now reviews the latest research into the causes of dyslexia. Neuroimaging studies may give early notice of impending dyslexia, and it is hoped that early interventions may lessen the impact of dyslexia. Learning occurs in many settings. Humans uniquely use the formalized settings of schools and curriculum. Infants and children also do plenty of learning outside these settings, often intermingling social interactions. Meltzoff et al. (p. 284) survey the variety of learning contexts that people experience and discuss how recent advances in neuroscience and robotics are driving a new synthesis of learning. Human learning is distinguished by the range and complexity of skills that can be learned and the degree of abstraction that can be achieved compared with those of other species. Homo sapiens is also the only species that has developed formal ways to enhance learning: teachers, schools, and curricula. Human infants have an intense interest in people and their behavior and possess powerful implicit learning mechanisms that are affected by social interaction. Neuroscientists are beginning to understand the brain mechanisms underlying learning and how shared brain systems for perception and action support social learning. Machine learning algorithms are being developed that allow robots and computers to learn autonomously. New insights from many different fields are converging to create a new science of learning that may transform educational practices.

A perceptual interference account of acquisition difficulties for non-native phonemes

This article presents an account of how early language experience can impede the acquisition of non-native phonemes during adulthood. The hypothesis is that early language experience alters relatively low-level perceptual processing, and that these changes interfere with the formation and adaptability of higher-level linguistic representations. Supporting data are presented from an experiment that tested the perception of English /r/ and /l/ by Japanese, German, and American adults. The underlying perceptual spaces for these phonemes were mapped using multidimensional scaling and compared to native-language categorization judgments. The results demonstrate that Japanese adults are most sensitive to an acoustic cue, F2, that is irrelevant to the English /r/-/l/ categorization. German adults, in contrast, have relatively high sensitivity to more critical acoustic cues. The results show how language-specific perceptual processing can alter the relative salience of within- and between-category acoustic variation, and thereby interfere with second language acquisition.

Speech perception by the chinchilla: Identification functions for synthetic VOT stimuli

In an attempt to clearly differentiate perceptual effects that are attributable to ’’auditory’’ and ’’phonetic’’ levels of processing in speech perception we have undertaken a series of experiments with animal listeners. Four chinchillas (Chinchilla laniger) were trained to respond differently to the ’’endpoints’’ of a synthetic alveolar speech continuum (0 ms VOT and +80 ms VOT) and were then tested in a generalization paradigm with the VOT stimuli between these endpoints. The resulting identification functions were nearly identical to those obtained with adult English‐speaking listeners. To test the generality of this agreement, the animals were then tested with synthetic stimuli that had labial and velar places of articulation. As a whole, the functions produced by the two species were very similar; the same relative locations of the phonetic boundaries, with lowest VOT boundaries for labial stimuli and highest for velar stimuli, were obtained for each animal and human subject. No significant differenc...

An association between mothers' speech clarity and infants' speech discrimination skills

The quality of speech directed towards infants may play an important role in infants’ language development. However, few studies have examined the link between the two. We examined the correlation between maternal speech clarity and infant speech perception performance in two groups of Mandarin-speaking mother‐infant pairs. Maternal speech clarity was assessed using the degree of expansion of the vowel space, a measure previously shown to reflect the intelligibility of words and sentences. Speech discrimination in the infants (6‐8 and 10‐12-month-olds) was measured using a head-turn task. The results show that mothers’ vowel space area is significantly correlated with infants’ speech discrimination performance. Socioeconomic data from both parents show that the result cannot be attributed to parental socioeconomic factors. This study is correlational and therefore a causal relationship cannot be firmly established. However, the results are consistent with the view that maternal speech clarity directly affects infants’ early language learning.

Speech perception in early infancy: perceptual constancy for spectrally dissimilar vowel categories.

While numerous studies on infant perception demonstrate the infants ability to discriminate individual speech-sound pairs, very few demonstrate the infants ability to recognize the similarity among phonetic units when they occur in different phonetic contexts, in different positions in a syllable, or when they are spoken by different talkers. In two studies, six-month-old infants demonstrated the ability to distinguish two spectrally dissimilar vowel categories (/a/ and /i/) in which the vowel tokens were generated to simulate tokens produced by a male, a female, and a child talker. In experiment I, the infants were initially trained to discriminate the /a/ and /i/ tokens produced by the computer-simulated male voice. They were then gradually exposed to a number of novel tokens in a progressive transfer-of-learning task. In experiment II, the infants were initially trained to discriminate the same vowell contrast, but were then immediately tested with all of the tokens in both vowel categories. In both experiments the infants demonstrated rapid transfer of learning from the training tokens produced by the male talker to the tokens produced by female and child talkers. Both experiments provide strong evidence that the six-month-old infant recognizes acoustic categories that conform to the vowel categories perceived by adult speakers of English.

Integrating speech information across talkers, gender, and sensory modality: female faces and male voices in the McGurk effect.

Studies of the McGurk effect have shown that when discrepant phonetic information is delivered to the auditory and visual modalities, the information is combined into a new percept not originally presented to either modality. In typical experiments, the auditory and visual speech signals are generated by the same talker. The present experiment examined whether a discrepancy in the gender of the talker between the auditory and visual signals would influence the magnitude of the McGurk effect. A male talker’s voice was dubbed onto a videotape containing a female talker’s face, and vice versa. The gender-incongruent videotapes were compared with gender-congruent videotapes, in which a male talker’s voice was dubbed onto a male face and a female talker’s voice was dubbed onto a female face. Even though there was a clear incompatibility in talker characteristics between the auditory and visual signals on the incongruent videotapes, the resulting magnitude of the McGurk effectwas not significantly different for the incongruent as opposed to the congruent videotapes. The results indicate that the mechanism for integrating speech information from the auditory and the visual modalities is not disrupted by a gender incompatibility even when it is perceptually apparent. The findings are compatible with the theoretical notion that information about voice characteristics of the talker is extracted and used to normalize the speech signal at an early stage of phonetic processing, prior to the integration of the auditory and the visual information.