The development of infant sensitivity to biomechanical motions

3 experiments were conducted to examine infant sensitivity at 20, 30, and 36 weeks of age to the 3-dimensional structure of a human form specified through biomechanical motions. All 3 experiments manipulated occlusion information in computer-generated arrays of point-lights moving as if attached to the major joints and head of a person walking. These displays are readily recognized as persons by adults when occlusion information is present, but not when it is absent or inconsistent with the implicit structure of the human body. Converging findings from Experiments 1 and 2 suggested that 36-week-old infants were sensitive to the presence of occlusion information in point-light walker displays; neither 20- nor 30-week-old infants showed any sensitivity to this information. The results of Experiment 3 revealed further that 36-week-old infants were sensitive to whether or not the pattern of occlusion was consistent with the implicit form of the human body, but only when the displays were presented in an upright orientation. These findings are interpreted as suggesting that infants, by 36 weeks of age, are extracting fundamental properties necessary for interpreting a point-light display as a person.     

Soothing pain-elicited distress in infants with swaddling and pacifiers

The effectiveness of pacifiers and swaddling in reducing pain-induced distress was compared in 2-week-old infants who underwent heel-sticks and 2-month-old infants who received injections. Crying, state, and heart rate were measured on 32 infants at each age during baseline, the stress of heel-stick or injection, and during 3-min soothing intervention and postintervention periods. At 2 weeks, infants' HR levels and crying declined significantly more rapidly in the pacifier than in the swaddling condition. At 2 months, both conditions produced similar rates of decline in HR and crying. At both ages, infants in the pacifier group spent significantly more time in an alert state than did swaddled infants. Following termination of the intervention at both ages, HR and crying tended to rebound more in the pacifier than in the swaddling group. Swaddling and pacifiers thus reduce pain-elicited distress differently.     

Infant Differences in Rate of Visual Encoding

To clarify the basis for infant differences in rate of visual encoding, the eye movements of a sample of 9 12-week-old infants were recorded throughout an encoding experiment. Results showed that the more slowly encoding infants scanned less extensively over the stimulus, often spent extended intervals in the continuous inspection of one part of the figure, and frequently engaged in prolonged fixations. A second experiment provided comparable scanning data from a sample of 9 2-week-old infants. There were significant age differences in the manner of visual scanning, and the scanning style of the more slowly encoding 12-week-old infants proved to be more like that of the younger infants. Possible explanations for both the between-age and within-age differences are proposed.     

The effect of stimulus complexity on infant visual attention and habituation.

Infant visual attention and habituation were examined with a procedure providing independent assessment of an infant's latency of orienting to a pattern (attention getting) and his subsequent fixation of that pattern (attention holding). 18 male and 18 female, 17-week-old infants were given 2 trials with a red circle, 16 trials with either a 2 times 2, 8 times 8, or 24 times 24 checkerboard pattern, then 2 more red-circle trials. The major results were that habituation occurred in fixation time with males habituating more than females, and that a general decrease occurred in latency with females selectively increasing or decreasing their latency depending upon the pattern they had previously seen. These results indicated the necessity of separating attention-getting from attention-holding measures and that both sexes remembered something about the visual patterns but demonstrated that memory differently.     

Imitation or Exploration? Young Infants' Matching of Adults' Oral Gestures

The claim that very young infants can imitate rests largely on reports that infants match adult displays of mouth opening (MO) and tongue protrusion (TP). Recent reviews suggest that only tongue protruding is reliably matched by young infants. This study tests the proposal that infants' "imitation" of tongue protruding reflects a coincidental match between a sight that infants find interesting and a behavior by which infants express interest. In Study 1, 4-week-old infants who looked longer at a nonsocial light display also produced TPs at higher rates than infants showing less interest. In Study 2, 4-week-old infants showed more interest in (looked longer at) a tongue-protruding adult face than a mouth-opening face. Study 3 tracked 2 infants' responses to interesting objects for several weeks before and after the onset of manual reaching. Both infants produced tongue protrusions in response to objects within reach before but not after reaching developed. Together, the results of the 3 studies suggest that infants' tongue protrusions in response to a tongue-protruding adult reflect very early attempts at oral exploration of interesting objects.     

Hand, Arm, and Facial Actions of Young Infants to a Social and Nonsocial Stimulus

Do 9-15-week-old infants produce differentially organized hand and arm actions in relation to affective states when presented with social and nonsocial stimuli? This question was examined by observing 8 infants longitudinally. They were observed when facing their active and passive mother and an active and passive doll during 4 visits at biweekly intervals. Videotapes were coded in real time using the following measures: Vocalization, Gaze, and Gaze Avert; for face, Smiling, Distressed, and Neutral; for hands, Pointing, Open, Curled, and Closed; and for arms, Extended and At Side. Co-occurrence and lag sequential analyses showed that hand actions were organized with other infant actions to form unique behavioral linkages in each of the 4 conditions. The implications of these findings for the development of nonverbal communication are discussed.     

Continuous vowel discrimination in normal and at risk infants.

The present study investigated vowel discrimination in 2-week-old infants using a nonnutritive, high-amplitude sucking measure in a habituation-dishabituation paradigm. Infants were presented with pairs of vowel stimuli differing in equal logarithmic steps along the /i/ to /I/ continuum. Stimulus pairs of equal acoustic differences were selected to be either within or between the adult phonetic categories. Infants were divided into 3 experimental stimulus shift conditions: within category, between category, and control. Using a scoring system to asses perinatal events, half the infants in each condition were categorized as being at "higher risk" for developmental (p less than .05) were found between the control and both the within and between phonetic category conditions. No effects due to risk score population differences proved to be significant. These results indicate that 8-week-old infants discriminate the vowels /i/ and /I/ in a continuous as opposed to a categorical manner. Some differences were noted in response patterns between high- and low-risk score infants.     

Location, location, location: development of spatiotemporal sequence learning in infancy

We investigated infants' sensitivity to spatiotemporal structure. In Experiment 1, circles appeared in a statistically defined spatial pattern. At test 11-month-olds, but not 8-month-olds, looked longer at a novel spatial sequence. Experiment 2 presented different color/shape stimuli, but only the location sequence was violated during test; 8-month-olds preferred the novel spatial structure, but 5-month-olds did not. In Experiment 3, the locations but not color/shape pairings were constant at test; 5-month-olds showed a novelty preference. Experiment 4 examined "online learning": We recorded eye movements of 8-month-olds watching a spatiotemporal sequence. Saccade latencies to predictable locations decreased. We argue that temporal order statistics involving informative spatial relations become available to infants during the first year after birth, assisted by multiple cues.     

Integration of Sequential Information for Shape Perception by Infants: A Developmental Study

Perception of form by spatiotemporal integration was investigated in 3 experiments. In the first, infants aged 8, 10, and 12 months were tested using a novelty-preference procedure to determine the earliest age at which recognition of rectilinear and curvilinear form occurred. Infants were shown a light-point tracing of the outline of a figure, followed by simultaneous presentation of 2 test objects, one of the same shape as the tracing and one of a different shape. The tracing was double the size of the test objects. Only infants in the oldest group responded selectively by looking longer at the object of different shape. In the second experiment with 12-month-old infants only, it was shown that recognition of rectilinear, but not curvilinear, form occurred despite a difference in the orientation and size of tracing and object. Computer-generated tracings were used in the final experiment to compare form recognition for 2D and 3D stimuli. Selective responding occurred only for the latter. These findings show that by 12 months infants perceive the correspondence between the figural properties of a tracing and its extended form, but that this perception is dependent on the provision of depth cues.     

Variations in intra-oral stimulation and nutritive sucking.

Sucking records were made from 24 infants, aged 3-4 days, fed small amounts of their usual formula from nipples of different sizes (5/16-, 8/16-, and 11/16-inch diam). Polygraphic and observer measures showed that the large nipple elicited fewer sucks and a slower sucking rate; 5 infants seen on 2 successive days showed a more marked nipple preference on the second day. The results show that intra-oral stimuli control sucking for a nutriment in much the same way as they have already been shown to control nonnutritive sucking.     

Development of subordinate-level categorization in 3- to 7-month-old infants

Visual preference procedures were used to investigate development of perceptually based subordinate-level categorization in 3- to 7-month-old infants. Experiments 1 and 2 demonstrated that 3- to 4-month-olds did not form category representations for photographic exemplars of subordinate-level classes of cats and dogs (i.e., Siamese vs. Tabby, Beagle vs. Saint Bernard). Experiments 3 though 5 showed that 6- and 7-month-olds formed a category representation for Tabby that excluded Siamese and a category representation for Saint Bernard that excluded Beagle, but they did not form a category representation for Siamese that excluded Tabby or a category representation for Beagle that excluded Saint Bernard. The findings are consistent with a differentiation-driven view of early perceptual category development from global to basic to subordinate levels.     

Infants' attention to patterned stimuli: developmental change from 3 to 12 months of age

To examine the development of look duration as a function of age and stimulus type, 14- to 52-week-old infants were shown static and dynamic versions of faces, Sesame Street material, and achromatic patterns for 20 s of accumulated looking. Heart rate was recorded during looking and parsed into stimulus orienting, sustained attention, and attention termination phases. Infants' peak look durations indicated that prior to 26 weeks there was a linear decrease with age for all stimuli. Older infants' look durations continued to decline for patterns but increased for Sesame Street and faces. Measures of heart rate change during sustained attention and the proportion of time spent in each phase of attention confirmed infants' greater engagement with the more complex stimuli.     

General and task-related experiences affect early object interaction

The effects of 2 weeks of no, general, and task-related enhanced movement experiences on 8- to 12-week-old infants' (N = 30) hand and foot interactions with objects were assessed using standard video and motion analysis. For hand-object interaction ability, general and task experience led to greater success than did no experience, and task experience led to greater success than did general experience. Only general experience led to greater success for foot-object interaction ability. Experiences therefore resulted in differential effects depending on which limbs infants used. The results suggest that different movement experiences can advance infants' earliest object interactions. They also indicate that even early purposeful behaviors result from a complex interplay of experience, current ability, and task demands.     

Relationship of Apgar scores and Bayley mental and motor scores.

Infants with 0-3 Apgar scores at 1 minute had significantly lower 8-month mental and motor scores than infants with 7-10 scores and significantly lower mental but not motor scores than infants with 4-6 Apgar scores. Correlations indicated significant relationships (independent of birth weight) between Apgar scores and Bayley mental and motor scores for random, Colored Portuguese, and total samples but not for Negroes and whites. Results demonstrated a significant difference in Apgar scores by 8-month classifications with significantly lower scores for children classified as abnormal, and by longevity with significantly lower scores for neonates who died within 2 days.     

Developmental changes in the scanning of faces by young infants.

6 1-month-old infants and 6 2-month-old infants each viewed 3 faces (his mother's, a strange woman's, and a strange man's) while his eye movements were recorded by corneal photography. The 1-month-olds fixated away from the faces most of the time, and they looked at their mothers even less often than at the strangers. When they did fixate a face, they usually chose a limited portion of the perimeter. By constrast, 2-month-olds fixated the faces most of the time, looked at more features, and were more likely to look at internal features, especially the eyes. This scanning resembles that reported previously for 2-dimensional shapes, although in some respects it appears unique to faces.     

The effect of prior practice on memory reactivation and generalization

Three experiments examined the effect of practice on memory performance by 18-month-old infants. Infants were tested using an imitation paradigm; an adult demonstrated a series of actions with objects and infants were given the opportunity to reproduce those actions following a delay. Some infants practiced the target actions before the retention interval (practice) and some did not (no practice). In Experiment 1, a reminder treatment alleviated forgetting by infants who practiced but failed to alleviate forgetting by infants who did not practice. In Experiments 2A and 2B, infants who practiced generalized to novel test stimuli after a 24-hr delay, whereas infants without practice did not. Results suggest practice influences the accessibility and generality of infants' memories.     

Infants' attentional responses to frequency modulated sweeps

In 3 experiments, the attentional responses of 4-month-old infants to frequency-modulated (FM) sweeps corresponding to the frequency range of adult-to-infant and adult-to-adult intonation patterns were assessed. In Experiment 1, infants were observed to discriminate "exaggerated" (i.e., adult-to-infant) FM sweeps from "normal" (i.e., adult-to-adult) FM sweeps in a habituation-dishabituation paradigm but did not selectively attend to one over the other. In Experiment 2, where the same stimuli were used in a paired-comparison paradigm, again no differential attention was observed. In Experiment 3, the most exaggerated sweep was paired against a continuous, monotonic pure tone, but again no difference in salience was observed. These data suggest that the extent of modulation or intonation of an auditory stimulus per se does not constitute a salient cue for infants' attention to sound.     

The development of audiovisual speech perception in Mandarin-speaking children: Evidence from the McGurk paradigm

The developmental trajectory of audiovisual speech perception in Mandarin-speaking children remains understudied. This cross-sectional study in Mandarin-speaking 3- to 4-year-old, 5- to 6-year-old, 7- to 8-year-old children, and adults from Xiamen, China (n = 87, 44 males) investigated this issue using the McGurk paradigm with three levels of auditory noise. For the identification of congruent stimuli, 3- to 4-year-olds underperformed older groups whose performances were comparable. For the perception of the incongruent stimuli, a developmental shift was observed as 3- to 4-year-olds made significantly more audio-dominant but fewer audiovisual-integrated responses to incongruent stimuli than older groups. With increasing auditory noise, the difference between children and adults widened in identifying congruent stimuli but narrowed in perceiving incongruent ones. The findings regarding noise effects agree with the statistically optimal hypothesis.     

Hemispheric asymmetry in a face discrimination task in infants

A right-hemisphere advantage in a mother's face recognition task in infants aged between 4 and 10 months was found to exist by de Schonen, Gil de Diaz, and Mathivet. The present study was designed to test (a) whether the right-hemisphere advantage would still prevail if the task requirements were different from those in the previous study, and (b) whether any information was communicated from one hemisphere to the other. 18-42-week-old infants were presented with an operant conditioning situation where they had to discriminate between their mother's and a stranger's face within one visual hemifield. Transfer of learning from one visual hemifield to the other was also measured. The results confirm the existence of a right-hemisphere advantage in discriminating between face stimuli. This advantage was weaker in the female than in the male population. No hemispheric transfer of learning was observed to occur.