Generalization of deferred imitation during the first year of life

Infants first generalize across contexts and cues at 3 months of age in operant tasks but not until 12 months of age in imitation tasks. Three experiments using an imitation task examined whether infants younger than 12 months of age might generalize imitation if conditions were more like those in operant studies. Infants sat on a distinctive mat in a room in their home (the context) while an adult modeled actions on a hand puppet (the cue). When they were tested 24 h later, 6-month-olds generalized imitation when either the mat or the room (but not both) differed, whereas 9-month-olds generalized when both the mat and the room differed. In addition, 9-month-olds who imitated immediately also generalized to a novel test cue, whereas 6-month-olds did not. These results parallel results from operant studies and reveal that the similarity between the conditions of encoding and retrieval-not the type of task-determines whether infants generalize. The findings offer further evidence that memory development during infancy is a continuous function.     

Developing knowledge of objects' motion properties in infancy

Three experiments with a novel variation of the inductive generalization procedure examined 18- and 22-month-olds' knowledge of objects' motion properties. Infants observed simple air and land movements modeled with an appropriate category member (e.g. dog) or an ambiguous block and were allowed to imitate with one or more of four exemplars. The experiments show that 18-month-olds' knowledge of land motions is grounded in causally relevant object parts, whereas 22-month-olds relate such motions more broadly to appropriate category members. Infants' basis for generalizing air motions suggested that at 22 months they have little knowledge about objects from that domain. The results are discussed in relation to the early development of the animate-inanimate distinction and the nature of the inductive generalization task.     

Motion and edge sensitivity in perception of object unity

Although much evidence indicates that young infants perceive unitary objects by analyzing patterns of motion, infants' abilities to perceive object unity by analyzing Gestalt properties and by integrating distinct views of an object over time are in dispute. To address these controversies, four experiments investigated adults' and infants' perception of the unity of a center-occluded, moving rod with misaligned visible edges. Both alignment information and depth information affected adults' and infants' perception of object unity in similar ways, and infants perceived object unity by integrating information about object features over time. However, infants perceived a moving, misaligned, three-dimensional object as indeterminate in its connectedness, whereas adults perceived it as connected behind the occluder. These findings indicate that the effectiveness of common motion in specifying unified surfaces across an occluder is reduced by misalignment of edges. Alignment information enhances perception of object unity either by serving directly as information for unity or by optimizing the detectability of motion-carried information for unity. In addition, young infants are able to retain information about edge orientation over short intervals in determining connectedness via a process of spatiotemporal integration.     

Behavioural development in a matching-to-sample task and token use by an infant chimpanzee reared by his mother

We investigated the behavioural and cognitive development of a captive male infant chimpanzee, Ayumu, raised by his mother, Ai. Here we report Ayumu's achievements up to the age of 2 years and 3 months, in the context of complex computer-controlled tasks. From soon after birth, Ayumu had been present during an experiment performed by his mother. The task consisted of two phases, a matching-to-sample task in which she received token rewards, and the insertion of these tokens into a vending machine to obtain food rewards. Ayumu himself received no reward or encouragement from humans for any of the actions he exhibited during the experiment. At the age of 9 months and 3 weeks, Ayumu performed his first matching-to-sample trial. At around 1 year and 3 months, he began to perform them consistently. Also during this period, he frequently stole food rewards from his mother. At 2 years and 3 months, Ayumu succeeded for the first time in inserting a token into the vending machine. Once he had succeeded in using a token, he performed both phases of the task in sequence 20 times consecutively. The infant's behaviour was not shaped by food rewards but by a strong motivation to copy his mother's behaviour. Our observations of Ayumu thus mirror the learning processes shown by wild chimpanzees.     

Cognitive development in object manipulation by infant chimpanzees

This study focuses on the development of spontaneous object manipulation in three infant chimpanzees during their first 2 years of life. The three infants were raised by their biological mothers who lived among a group of chimpanzees. A human tester conducted a series of cognitive tests in a triadic situation where mothers collaborated with the researcher during the testing of the infants. Four tasks were presented, taken from normative studies of cognitive development of Japanese infants: inserting objects into corresponding holes in a box, seriating nesting cups, inserting variously shaped objects into corresponding holes in a template, and stacking up wooden blocks. The mothers had already acquired skills to perform these manipulation tasks. The infants were free to observe the mothers' manipulative behavior from immediately after birth. We focused on object–object combinations that were made spontaneously by the infant chimpanzees, without providing food reinforcement for any specific behavior that the infants performed. The three main findings can be summarized as follows. First, there was precocious appearance of object–object combination in infant chimpanzees: the age of onset (8–11 months) was comparable to that in humans (around 10 months old).Second, object–object combinations in chimpanzees remained at a low frequency between 11 and 16 months, then increased dramatically at the age of approximately 1.5 years. At the same time, the accuracy of these object–object combinations also increased. Third, chimpanzee infants showed inserting behavior frequently and from an early age but they did not exhibit stacking behavior during their first 2 years of life, in clear contrast to human data.     

Establishing Functional Classes In A Chimpanzee (Pan troglodytes) With A Two-item Sequential-Responding Procedure

A 9-year-old female chimpanzee was trained on a two-item sequential-responding task. Attempts were made with successive-reversal training to establish functional classes. In Experiment 1, the subject was exposed to between-session successive-reversal training in which one of two pairs of stimuli was reversed, and transfer of reversal responding to the other pair was tested with nonreinforcement probe trials. She did not show transfer during the course of reversals. Stimulus control established in the original training was maintained on nonreinforcement probe trials. In Experiment 2, within-session reversals were introduced. She showed transfer from the initially reversed pair to the other. The results were consistent with Vaughan's (1988) results with pigeons on successive discriminations, which indicated the formation of functional classes. In Experiment 3, crossover and wild-card tests were conducted to clarify the stimulus control of sequential responding. The results suggested that the sequential responding was controlled only by the first stimulus of each pair. To establish control by both first and second stimuli, trial-unique stimuli or wild cards were substituted for one of the items of the lists in Experiment 4. Further transfer tests, in which stimuli for the two new pairs appeared, were also given to the subject. She successfully responded to these two merged lists and reversed the order as the result of reversal training.     

Evidence of observer reliability for the Fagan Test of Infant Intelligence (FTII)

To obtain estimates of observer reliability, the Fagan Test of Infant Intelligence (FTII) apparatus was modified to allow the infants' performance to be videotaped. Based upon results of 25 infants scored once during time of testing and again 2 years later using the videotape version, interobserver and intraobserver reliabilities obtained for percent novelty preference (test rounds), total number of looks (familiarization and test rounds), and mean fixation (familiarization and test rounds) were mostly very high for each round (M r = .92, SD = .04). The videotaped infants' scores did not differ significantly from those of a comparable sample of infants who were tested using an unmodified apparatus.     

Correlation between performance and quantity/variability of leg exploration in a contingency learning task during infancy

Quantity and quality of motor exploration are proposed to be fundamental for infant motor development. However, it is still not clear what types of motor exploration contribute to learning. To determine whether changes in quantity of leg movement and/or variability of leg acceleration are related to performance in a contingency learning task, twenty 6–8-month-old infants with typical development participated in a contingency learning task. During this task, a robot provided reinforcement when the infant’s right leg peak acceleration was above an individualized threshold. The correlation coefficient between the infant’s performance and the change in quantity of right leg movement, linear variability, and nonlinear variability of right leg movement acceleration from baseline were calculated. Simple linear regression and multiple linear regression were calculated to explain the contribution of each variable to the performance individually and collectively. We found significant correlation between the performance and the change in quantity of right leg movement (r = 0.86, p < 0.001), linear variability (r = 0.71, p < 0.001), and nonlinear variability (r = 0.62, p = 0.004) of right leg movement acceleration, respectively. However, multiple linear regression showed that only quantity and linear variability of leg movements were significant predicting factors for the performance ratio (p < 0.001, adjusted R² = 0.94). These results indicated that the quantity of exploration and variable exploratory strategies could be critical for the motor learning process during infancy.     

Another look at “tummy time” for primary plagiocephaly prevention and motor development

It is three decades since it was recommended that infants sleep on the back to reduce risk of sudden unexpected infant death (SUID). The SUID prevention program is known as “back to sleep” or “safe sleeping”, and this initiative is not questioned. Sleeping on the back is associated with, but not the cause of, the development of infant positional plagiocephaly, also known as deformational or a non-synostotic misshapen head when the skull sutures are open, not fused. This paper provides a synthesis of the history and impact of positional plagiocephaly. It includes a scoping review of plagiocephaly prevention facilitating motor development and reveals few articles on primary prevention which aims to prevent it developing in the first place. It is concerning that preschool-aged children with a history of infant plagiocephaly continued to receive lower developmental scores, particularly in motor development, than unaffected controls, and this may be a marker of developmental delay. Tummy-time (prone) for play is the mainstay of plagiocephaly prevention advice to minimize development of plagiocephaly and to facilitate infant motor development, particularly head control. While tummy-time has shown benefit for infant development, there is limited evidence of its effectiveness in preventing plagiocephaly and some evidence that it promotes only prone-specific motor skills. Most of the published literature is concerned with treatment post-diagnosis, in the form of reviews, or clinical notes. There is a plethora of opinion articles reinforcing tummy-time from birth for plagiocephaly prevention. The review shows that there are gaps in advice for early infant development of head control. An accepted test of head control in infants is “pull to sit” from supine which demonstrates antigravity strength of the neck flexors and coordination of the head and neck when the infant is drawn to sit from supine. This motor skill was cited as achievable by 4 months in the earliest paper on plagiocephaly in 1996. Physical therapists and others should revisit the mechanism of early infant head control development against gravity, particularly antigravity head, neck and trunk coordinated flexion movement in supine, as there has been little attention to early facilitation of this motor skill as a plagiocephaly prevention strategy. This may be achieved by considering “face time” as well as tummy time for primary prevention of plagiocephaly.