Gerald W. McRoberts

Examination of Perceptual Reorganization for Nonnative Speech Contrasts: Zulu Click Discrimination by English­ Speaking Adults and Infants

The language environment modifies the speech perception abilities found in early development. In particular, adults have difficulty perceiving many nonnative contrasts that young infants discriminate. The underlying perceptual reorganization apparently occurs by 10-12 months. According to one view, it depends on experiential effects on psychoacoustic mechanisms. Alternatively, phonological development has been held responsible, with perception influenced by whether the nonnative sounds occur allophonically in the native language. We hypothesized that a phonemic process appears around 10-12 months that assimilates speech sounds to native categories whenever possible; otherwise, they are perceived in auditory or phonetic (articulatory) terms. We tested this with English-speaking listeners by using Zulu click contrasts. Adults discriminated the click contrasts; performance on the most difficult (80% correct) was not diminished even when the most obvious acoustic difference was eliminated. Infants showed good discrimination of the acoustically modified contrast even by 12-14 months. Together with earlier reports of developmental change in perception of nonnative contrasts, these findings support a phonological explanation of language-specific reorganization in speech perception.

Rapid Gains in Speed of Verbal Processing by Infants in the 2nd Year

Infants improve substantially in language ability during their 2nd year. Research on the early development of speech production shows that vocabulary begins to expand rapidly around the age of 18 months. During this period, infants also make impressive gains in understanding spoken language. We examined the time course of word recognition in infants ages 15 to 24 months, tracking their eye movements as they looked at pictures in response to familiar spoken words. The speed and efficiency of verbal processing increased dramatically over the 2nd year. Although 15-month-old infants did not orient to the correct picture until after the target word was spoken, 24-month-olds were significantly faster, shifting their gaze to the correct picture before the end of the spoken word. By 2 years of age, children are progressing toward the highly efficient performance of adults, making decisions about words based on incomplete acoustic information.

Development of sensitivity to information for impending collision

Infants were tested in three experiments to study the development of sensitivity to information for impending collision and to investigate the hypothesis that postural changes of very young infants in response to an approaching object are of a tracking rather than of a defensive nature. Experiment 1 involved the presentation of three types of shadow projection displays, specifying (1) collision, (2) noncollision, and (3) a nonexpanding rising contour, to infants from 1 to 9 months of age. Avoidance of collision appears to be absent in 1- to 2-month-olds, begins to develop in 4- to 6-month-olds, and is present in 8- to 9-month-old infants. In Experiment 2, 1- to 2-month-old infants were presented with optical expansion patterns which specified collision and noncollision. The top contour of these displays stayed at eye level. No significant difference was observed between reaction to the collision and the noncollision displays, suggesting that the young infants were tracking the displays and not attempting to avoid collision. Experiment 3 was designed to determine whether an approaching real object might elicit an avoidance response in infants not sensitive to an optical display specifying collision. No evidence of avoidance behavior was observed in the 1- to 2-month-olds; however, avoidance, as indexed by blinking, does appear to be present at 4 months of age.

Young infants’ perception of liquid coarticulatory influences on following stop consonants

Phonetic segments are coarticulated in speech. Accordingly, the articulatory and acoustic properties of the speech signal during the time frame traditionally identified with a given phoneme are highly context-sensitive. For example, due to carryover coarticulation, the front tongue-tip position for HI results in more fronted tongue-body contact for a /g/ preceded by /l/ than for a /g/ preceded by /r/. Perception by mature listeners shows a complementary sensitivity—when a synthetic /da/-/ga/ continuum is preceded by either /al/ or /ar/, adults hear more /g/s following HI rather than Irl. That is, some of the fronting information in the temporal domain of the stop is perceptually attributed to /l/ (Mann, 1980). We replicated this finding and extended it to a signaldetection test of discrimination with adults, using triads of disyllables. Three equidistant items from a /da/-/ga/ continuum were used preceded by /al/ and /ar/. In the identification test, adults had identified item ga5 as “ga”, and dal as “da”, following both /al/ and /ar/, whereas they identified the crucial item d/ga3 predominantly as “ga” after /al/ but as “da” after /ar/. In the discrimination test, they discriminated d/ga3 from dal preceded by /al/ but not /ar/; compatibly, they discriminated d/ga3 readily from ga5 preceded by /ar/ but poorly preceded by /al/. We obtained similar results with 4-month-old infants. Following habituation to either ald/ga3 or ard/ga3, infants heard either the corresponding ga5 or dal disyllable. As predicted, the infants discrimi-nated d/ga3 from dal following /al/ but not /ar/; conversely, they discriminated d/ga3 from ga5 following /ar/ but not /al/. The results suggest that prelinguistic infants disentangle consonant-consonant coarticulatory influences in speech in an adult-like fashion.

Accommodation in mean f 0 during mother–infant and father–infant vocal interactions: a longitudinal case study

Reports that infants imitate the vocal pitch characteristics of adult caregivers (e.g. Lewis, 1936/1951) include Liebermans (1967; Lieberman, Ryalls & Rabson, 1982) claim that infants differentially adjust their vocal pitch or fundamental frequency (f0) towards that of their caregivers, resulting in higher mean pitch when interacting with mothers than when interacting with fathers. However, a recent cross-sectional study of infants at ages 0:8 to 0:9 and 1:0 failed to find evidence of differential pitch adjustment toward male and female caregivers (Siegel, Cooper, Morgan & Brennessie-Sarshad, 1990). A more sensitive test of Liebermans claims would be to use a longitudinal design, with spontaneous recording sessions repeated over many months. The current study presents data from a longitudinal case study of an infant recorded at ages 0:3, 0:7, 0:10, 1:3 and 1:5 interacting with each of her parents in spontaneous play sessions and in isolated play. The infant in our study did not demonstrate significant adjustment of her vocal pitch in the direction of either parent. However, we did find evidence for consistent adjustment by the parents, in accord with the literature on infant-directed speech and mother-infant dyadic interactions, which suggest that the parents adjusted their behavior to suit the infant more than vice versa.

The role of fundamental frequency in signaling linguistic stress and affect: Evidence for a dissociation

The fundamental frequency (F0) of the voice is used to convey information about both linguistic and affective distinctions. However, no research has directly investigated how these two types of distinctions are simultaneously encoded in speech production. This study provides evidence thatF0 prominences intended to convey linguistic or affective distinctions can be differentiated by their influence on the amount of final-syllableF0 rise used to signal a question. Specifically, a trading relation obtains when theF0 prominence is used to convey emphatic stress. That is, the amount of finalsyllableF0 rise decreases as theF0 prominence increases. When theF0 prominence is used to convey affect, no trading relation is observed.

Sex differences in performance and hemispheric organization for a nonverbal auditory task

Musically experienced and inexperienced men and women discriminated among fundamental-frequency contours presented either binaurally (i.e., same contour to both ears) or dichotically (i.e., different contours to each ear). On two separate occasions, males made significantly fewer errors than did females in the binaural condition, but not in the dichotic condition. Subjects with prior musical experience were superior to musically naive subjects in both conditions. The dichotic pitch task produced a left-ear advantage, which was unrelated to gender or musical experience. The results suggest that the male advantage on the binaural task reflects a sex difference in the coordination of the two hemispheres during conjoint processing of the same stimuli rather than a difference in the direction or degree of hemispheric specialization for these stimuli.

Immediate memory for pseudowords and phonological awareness are associated in adults and pre-reading children

This study investigated phonological components of reading skill at two ages, using a novel pseudoword repetition task for assessing phonological memory (PM). Pseudowords were designed to incorporate control over segmental, prosodic and lexical features. In Experiment 1, the materials were administered to 3- and 4-year-old children together with a standardized test of phonological awareness (PA). PA and pseudoword repetition showed a moderate positive correlation, independent of age. Experiment 2, which targeted young adults, employed the same pseudoword materials, with a different administration protocol, together with standardized indices of PA, other memory measures and decoding skill. The results showed moderate to strong positive correlations among our novel pseudoword repetition task, measures of PM and PA and decoding. Together, the findings demonstrate the feasibility of assessing PM with the same carefully controlled materials at widely spaced points in age, adding to present resources for assessing PM and better enabling future studies to map the development of relationships among phonological capabilities in both typically developing children and those with language-related impairments.

Infants’ attention to repeated speech and musical patterns

Previous investigations have shown that infants older than 5 months listen longer to speech with repeated utterances than to speech without utterance repetition. The present studies investigated whether infants also attend preferentially to repeated musical patterns. Musical phrases of four and five notes and ending with a rest were composed using several pitch contours and rhythmic patterns. Experiments 1 and 2 compared trials in which phrases were immediately repeated (AABBCC), to trials in which the same phrases occurred without repetition (ABCDE). In the first experiment, no listening preference for either trial type was found for 6‐ or 9‐month‐old infants. In experiment 2, silence was added after each phrase to assist infants in parsing the phrases. Infants again failed to show a listening preference. In experiment 3, trials of speech, half with repeated utterances and half without repeated utterances (from previous experiments), were interspersed with trials of repeated and nonrepeated music. Nine‐month‐olds demonstrated a preference for the repeated trials of both speech and music over nonrepeated trials of the same type. The fact that a preference for musical repetition is only obtained through induction (from verbal repetition) suggests that repeated speech may hold a special attentional status for infants. [Work was supported by Grants NIH—R15/DC005947 and NIH—R01/DC00403.]

The role of lexical access in spontaneous speech disfluencies

Pauses and hesitations in spontaneous speech are assumed to result from problems in various aspects of sentence planning. A causal role for difficulties with lexical access is suggested by theoretical accounts of speech production [Levelt, Speaking (1989)] and empirical studies showing that pauses are more likely before rare than common words in spontaneous speech [Maclay and Osgood (1959)]. In the present study, word frequency was manipulated in a picture‐naming task in which speakers produced the names of ten high‐ and ten low‐frequency pairs of standardized line drawings within a standard sentence frame (e.g., There is a snail to the left of the harp.). The mean frequency of occurrence for high‐ and low‐frequency items was 171.5 (range: 50–591) and 3.5 (range: 1–8) per million, respectively [H. Kucera and W. N. Francis, A Computational Analysis of Present‐day English (1967)]. Analyses indicate that low‐frequency pairs resulted in: (1) more pauses and word substitutions and (2) longer latencies to begin...