Perceiving non-native speech.

In a series of experiments using monosyllabic words produced by a native and a non-native speaker of English, native English speakers monitored the word-initial consonants of the words to decide which of two consonants was present on each trial. In some of the experiments, a secondary task of a linguistic nature, deciding whether the target-bearing word was a noun or verb, was also required. When the words were presented in silence, the native and non-native stimuli were processed in a like manner. Specifically, when the secondary task was not required, phonemic decisions tended to be made on the basis of prelexical information, whereas when the secondary task was required, they tended to be made on the basis of postlexical information (see Eimas, Marcovitz Hornstein, & Payton, 1990). However, when the listening conditions were degraded by presenting the words at a lower level and in noise, the two types of stimuli yielded different patterns. Native speech was processed as before, whereas for non-native speech phonemic decisions now tended to be made on the basis of postlexical information both when a secondary task was required and when it was not. The contrasting results for native and non-native speech are discussed in terms of models of phoneme processing.

Perceptual categorization of cat and dog silhouettes by 3- to 4-month-old infants.

Given evidence that silhouette information can be used by adults to form categorical representations at the basic level, four experiments utilizing the familiarization-novelty preference procedure were performed to examine whether 3- and 4-month-old infants could form categorical representations for cats versus dogs from the perceptual information available in silhouettes (e.g., global shape and external outline). Experiments 1 and 2 showed that infants could form individuated categorical representations for cat and dog silhouettes, whereas Experiments 3 and 4 revealed that infants could use silhouette information from the head, but not the body, to categorically separate the two species. These results indicate that general shape or external contour information that is centered about the head is sufficient for young infants to form individuated categorical representations for cats and dogs. The data thus provide information regarding the nature of the perceptual information that can be used by infants to form category representations for individual animal species and are discussed in terms of domain-general versus domain-specific processing accounts.

Segmental and syllabic representations in the perception of speech by young infants.

In a series of four experiments, the ability of 3- to 4-month-old infants to form categorical representations to syllable-initial consonants in monosyllabic stimuli (experiments 1 and 2) and to initial and final syllables in bisyllabic stimuli (experiments 3 and 4, respectively) was investigated. Experiment 1 yielded no evidence of categorical representations for the initial consonant. However, the results indicated that the four or six stimuli presented during the initial phase of familiarization had been remembered. The results of experiment 2, which employed a less stringent familiarization criterion, replicated the findings of experiment 1, although there was some evidence for categorization for infants whose familiarization performance more closely matched the weaker criterion. In experiment 3, there was strong evidence for a categorical representation of the initial syllable of bisyllabic stimuli for infants experiencing six familiar stimuli. In experiment 4, there was less robust evidence of categorization of the final syllable of bisyllabic stimuli, but again only when six familiar stimuli were experienced. The results were discussed in terms of the earliest representation of speech being syllables that could be modified by the rhythmic nature of the infant's native language.

Evidence for a global categorical representation of humans by young infants.

The representation of pictorial exemplars of humans by young infants was examined. Experiments 1B and 2 demonstrated an asymmetry with respect to the exclusivity of the categorical representations formed by 3- and 4-month-olds for humans and non-human animal species. The categorical representation for humans included novel humans, horses, cats, and fish, but excluded cars; the categorical representation for horses included novel horses, but excluded humans, fish, and cars. Experiment 2 also showed that the categorical representation for humans included exemplar information, whereas the categorical representation for non-human animal species was based on summary information. The asymmetry in categorization of human versus non-human animal species did not extend to the presumed more basic process of discrimination of individual humans versus non-human animals (Experiment 3). The findings suggest that a broad categorical representation of humans may be a cognitive reference point (or region) for young infants.

Perceptual differences in infant cries revealed by modifications of acoustic features.

Previous studies of infant cry acoustics and their perceptual significance have remained inconclusive as to the graded nature of cry production and perception and to the exact role and importance of particular acoustic features. In this study, a set of infant cries were digitally analyzed and resynthesized to form natural-sounding cries with varying fundamental frequency (F0), degrees of jitter (period to period variations in F0), and rise time (time for F0 to reach its maximum value). In a perceptual rating task, higher-F0 cries as well as cries with larger amounts of jitter tended to be given more negative ratings than were lower-F0 cries and cries with less jitter, respectively. The perceptual ratings of the rise time manipulations were inconclusive. This study demonstrated a perceptual effect of F0 and jitter independently of other parameters, consistent with current notions of infant cry gradedness. It was also shown that digital signal processing techniques can be fruitfully applied to infant cry research.

Internal structure of voicing categories in early infancy.

It is well established that young infants process speech in terms of perceptual categories that closely correspond to the phonetic categories of adult language users. Recently, Kuhl (1991) has provided evidence that this correspondence is not limited to the region of category boundaries: At least by 6-7 months of age, vowel categories of infants, like those of adults, have an internal perceptual structure. In the current experiments, which focused on a consonantal contrast, we found evidence of internally structured categories in even younger infants-3-4 months of age. The implications of these findings for the nature of the infant's earliest language-universal categories are discussed, as is the role of exposure to the native language in shaping these categories over the course of development.

Perceptual cues that permit categorical differentiation of animal species by infants.

Eight experiments were performed to determine the perceptual cues used by 3- and 4-month-old infants to categorically distinguish between perceptually similar natural animal species. These experiments provided evidence that information from the facial and head region, specifically, the internal features of the face and the external contour of the head, give the infant a necessary and sufficient basis to form a categorical representation for cats that excludes dogs. The results are discussed in terms of Johnson and Morton's (1991) theory of facial recognition and more general accounts of the information underlying categorical representations.

Phonemic restoration and integration during dichotic listening.

In a series of experiments, evidence was obtained for phonemic restoration when a word with the segment /s/ excised and replaced by silence and a comparable noise segment were presented dichotically. What has been called phonemic integration was also demonstrated by presenting the excised /s/ and the word with the /s/ removed and replaced by silence dichotically. Phonemic restoration and integration effects tended to be enhanced when barely audible versions of the excised /s/ or noise segment replaced the silence. Finally, phonemic integration was obtained when words with an excised CV syllable or VC rime were present dichotically together with the remainder of the word.

Development of exclusivity in perceptually based categories of young infants.

The exclusivity of perceptually defined categorical representations for natural animal categories in young infants was investigated. Previously, as well as in Experiment 1, evidence was obtained for a categorical representation for cats in 3- and 4-month-old infants that excluded dogs but included perceptually similar female lions after a number of different familiarization procedures. However, in Experiment 2 both dogs and female lions were found to be excluded when the initial familiarization with cats alone was followed by six pairings of familiar cats and novel lions intermingled with two added pairings of familiar cats. The present results indicate that a categorical representation can attain a high level of exclusivity during early infancy as a consequence of experience with exemplars of the contrasting categories that accents the perceptual similarities among members of a category and the perceptual differences among exemplars from different categories.

Studies on the formation of perceptually based basic-level categories in young infants.

A series of experiments examined the abilities of 3- and 4-month-old infants to form categorical representations to exemplars of natural kinds--cats and horses. These experiments also permitted assessment of the relative exclusivity of these representations--the extent to which they exclude exemplars from contrasting basic-level categories from the same superordinate category. We found that categorical representations could be formed for horses that excluded cats, zebras, and giraffes, and for cats that excluded horses and tigers but not female lions. Lions were, however, excluded from the representations of cats in 6- and 7-month-old infants. Evidence was also obtained for 2 a priori preferences for members of one category over another. The discussion examined the roles of similarity between the exemplars of the contrasting categories and those of the tested category on estimates of exclusivity and of spontaneous preferences on the formation and exclusivity of categorical representations.

Categorization in early infancy and the continuity of development.

Arguments and evidence are presented for the conclusion that the young infant's perceptually based categorical representations for natural kinds--animals in this case--are the basis for their mature conceptual counterparts. In addition, it is argued that conceptual development is continuous in nature and without the need for special developmental processes. A consideration of the development of the syllabic, segmental, and featural categories of phonology shows a more complex pattern of change--one marked by both continuities and discontinuities in the representations themselves and the processes that produce them.

Evidence for representations of perceptually similar natural categories by 3-month-old and 4-month-old infants.

The paired-preference procedure was used in a series of experiments to explore the abilities of infants aged 3 and 4 months to categorize photographic exemplars from natural (adult-defined) basic-level categories. The question of whether the categorical representations that were evidenced excluded members of a related, perceptually similar category was also investigated. Experiments 1-3 revealed that infants could form categorical representations for dogs and cats that excluded birds. Experiment 4 showed that the representation for cats also excluded dogs, but that the representation for dogs did not exclude cats. However, a supplementary experiment showed that the representation for dogs did exclude cats when the variability of the dog exemplars was reduced to match that of the cat exemplars. The results are discussed in terms of abilities necessary for the formation of more complex categorical representations.

A constraint on the discrimination of speech by young infants.

Three- and four-month-old infants were tested on their ability to discriminate the third-formant transitions sufficient to signal the syllable-medial stops [t] and [k]. The stimulus patterns consisted of an initial fricative [s], 20 or 100 msec of silence, and the vowel [a], whose initial formant transitions were appropriate for [t] or [k]. Discrimination only occurred when the duration of silence was 100 msec. This constraint on discrimination is discussed in terms of a psychoacoustic explanation based on forward masking and in terms of the hypothesis that the processing of speech signals involves a species-specific system dedicated to deriving a phonetic message.

A new version of duplex perception: evidence for phonetic and nonphonetic fusion.

In a series of experiments, a variant of duplex perception was investigated. In its original form, duplex perception is created by presenting an isolated transition to one ear and the remainder of the syllable, the standard base, to the other ear. Listeners hear a chirp at the ear receiving the isolated transition, and a full syllable at the ear receiving the base. The new version of duplex perception was created by presenting a third-formant transition in isolation to one ear and the same transition electronically mixed with the base to the other ear; the modified base now has all the information necessary for syllabic perception. With the new procedure, listeners reported hearing a chirp centered in the middle of their head and a syllable in the ear presented the modified base that was clearer than that produced by the isolated transition and standard base. They could also reliably choose the patterns that contained the additional transition in the base when attending to either the phonetic or nonphonetic sides of the duplex percept. In addition, when the fundamental frequency, onset time, and intensity of the isolated third-formant transition were varied relative to the base, the phonetic and nonphonetic (lateralization) percepts were differentially affected, although not always reliably. In general, nonphonetic fusion was more affected by large differences in these variables than was phonetic fusion. However, when two isolated third-formant transitions were presented dichotically, fusion and the resulting central location of the chirp failed markedly with relatively small differences in each variable. The results were discussed in terms of the role of fusion in the new version of duplex perception and the nature of the information that undergoes both phonetic and nonphonetic fusion.

Speech perception in children with histories of recurrent otitis media.

The present study investigated the ability of 5-year-old children to perceive differences in voice onset time (VOT) in naturally produced speech. Three groups of children whose hearing was within normal limits at the time of the experiment were tested on identification and discrimination tasks: (1) group C, in which the children had normal language abilities and no history of severe, recurrent otitis media (OM), (2) group OM, in which the children had histories of severe, recurrent OM but normal language abilities, and (3) group OM/DL, in which the children had histories of severe OM and delays in the acquisition of linguistic competence. Compared to group C, group OM/DL showed marked differences in their ability to identify and discriminate speech patterns. Their perception was less categorical, as well, in that there was less of a peak in the discrimination function at the region of the phoneme boundary. The performance of group OM fell between the other two groups, with deficits being more pronounced in the discrimination task than in the identification task. The results supported the idea that episodes of OM can produce periods of sensory deprivation that alter perceptual abilities. The relation of a history of OM to later language and academic difficulties was also considered.

Otitis media, hearing loss, and child development: a NICHD conference summary.

Growing evidence indicates that a significant relationship exists between the conductive hearing loss resulting from recurrent otitis media (OM) during the first 3-5 years of life and subsequent problems in acquisition of language and academic skills. To assess current knowledge of OM and its consequences for cognitive and linguistic development, to exchange viewpoints, and, if possible, to determine directions for future research, a conference was sponsored by the National Institute of Child Health and Human Development (NICHD). Among the epidemiologic studies cited, some found a very high incidence of OM in North American Indians and Eskimos, caused, according to one hypothesis, by a genetically different eustachian tube. Another researcher advised that basic language development should be carefully assessed in all cases of OM in young children. Conferees agreed that intervention programs must be developed and implemented until preventive measures are available. One model program emphasizes prevention of developmental difficulties based on the known and suspected sequelae of OM and on the known principles of language development. Conference participants recommended that all infants and young children, particularly those at risk, be examined for OM during regular medical checkups. In addition to treating the disorder, measures should be taken to deal with any significant hearing loss. If drug therapy is inadequate to clear effusion from the middle ear, surgery should be considered. Speech and language intervention should be undertaken when required.