Stacking of blocks by chimpanzees: developmental processes and physical understanding

The stacking-block task has been used to assess cognitive development in both humans and chimpanzees. The present study reports three aspects of stacking behavior in chimpanzees: spontaneous development, acquisition process following training, and physical understanding assessed through a cylindrical-block task. Over 3 years of longitudinal observation of block manipulation, one of three infant chimpanzees spontaneously started to stack up cubic blocks at the age of 2 years and 7 months. The other two infants began stacking up blocks at 3 years and 1 month, although only after the introduction of training by a human tester who rewarded stacking behavior. Cylindrical blocks were then introduced to assess physical understanding in object-object combinations in three infant (aged 3-4) and three adult chimpanzees. The flat surfaces of cylinders are suitable for stacking, while the rounded surface is not. Block manipulation was described using sequential codes and analyzed focusing on failure, cause, and solution in the task. Three of the six subjects (one infant and two adults) stacked up cylindrical blocks efficiently: frequently changing the cylinders' orientation without contacting the round side to other blocks. Rich experience in stacking cubes may facilitate subjects' stacking of novel, cylindrical shapes from the beginning. The other three subjects were less efficient in stacking cylinders and used variable strategies to achieve the goal. Nevertheless, they began to learn the effective way of stacking over the course of testing, after about 15 sessions (75 trials).     

The role of surface discontinuity and shape in 4-month-old infants' object segregation

This research examined whether 4-month-old infants use a discontinuity in an object's front surface to visually segregate a display into two separate objects, and whether object shape enables its use. In Experiment 1, infants saw a three-dimensional display composed of two parts with distinctly different shapes. Two groups of infants saw a display in which these two shapes were divided by a visible discontinuity in the front surface (i.e., a boundary between the two objects). One of these groups saw the display move apart at the discontinuity when a gloved hand pulled one object; the second group saw the two objects move together as a single unit. A third group saw a modified version of this display that had no discontinuity present. The results suggested that infants regarded the discontinuity as an indication that the display could be composed of more than one object. In Experiment 2, infants saw the same display, but with a shape that did not highlight the discontinuity. The infants in this study showed no evidence of using the discontinuity. Together, the findings suggest that 4-month-old infants use the surface discontinuity between two objects as an indication that multiple objects could be present in a display, but only when scanning the outer edges of the display leads them to attend to it.     

Habit outweighs planning in grasp selection for object manipulation

Object-directed grasping movements are adapted to intended interactions with an object. We address whether adjusting the grasp for object manipulation is controlled habitually, based on past experiences, or by goal-directed planning, based on an evaluation of the expected action outcomes. Therefore, we asked participants to grasp and rotate a dial. In such tasks, participants typically grasp the dial with an excursed, uncomfortable arm posture, which then allows to complete the dial rotation in a comfortable end-state. We extended this task by manipulating the contingency between the orientation of the grasp and the resulting end-state of the arm. A one-step (control) group rotated the dial to a single target. A two-step group rotated the dial to an initial target and then in the opposite direction. A three-step group rotated the dial to the initial target, then in the opposite direction, and then back to the initial target. During practice, the two-step and three-step groups reduced the excursion of their grasps, thus avoiding overly excursed arm postures after the second rotation. When the two-step and three-step groups were asked to execute one-step rotations, their grasps resembled those that were acquired during the two-step and three-step rotations, respectively. However, the carry-over was not complete. This suggests that adjusting grasps for forthcoming object manipulations is controlled by a mixture of habitual and goal-directed processes. In the present experiment, the former contributed approximately twice as much to grasp selection than the latter.     

Infants' reasoning about opaque and transparent occluders in an individuation task

There has been some debate about whether infants 10 months and younger can use featural information to individuate objects. The present research tested the hypothesis that negative results obtained with younger infants reflect limitations in information processing capacities rather than the inability to individuate objects based on featural differences. Infants aged 9.5 months saw one object (i.e. a ball) or two objects (i.e. a box and a ball) emerge successively to opposite sides of an opaque occluder. Infants then saw a single ball either behind a transparent occluder or without an occluder. Only the infants who saw the ball behind the transparent occluder correctly judged that the one-ball display was inconsistent with the box-ball sequence. These results suggest that: (a) infants categorize events involving opaque and transparent occluders as the same kind of physical situation (i.e. occlusion) and (b) support the notion that infants are more likely to give evidence of object individuation when they need to reason about one kind of event (i.e. occlusion) than when they must retrieve and compare categorically distinct events (i.e. occlusion and no-occlusion).     

A direct comparison of infants' use of featural and spatiotemporal information when individuating objects in a non-occlusion event-monitoring design

A central issue within the field of object individuation concerns the kind of information that infants rely on when they succeed in individuating objects. By means of the violation-of-expectation strategy, the present study reports a comparison of 8.0- and 6.5-month-old infants' use of featural and spatiotemporal information in a new non-occlusion event-monitoring design. Using a mirror setup the memory demands were minimized, because all apparent changes in the unexpected test events took place in full view of the infants. The results indicate that the 8.0- and 6.5-month-old infants individuated objects successfully regardless of whether they were provided with featural or spatiotemporal information. The results are discussed in relation to the relevant literature.     

Finger drawing by infant chimpanzees (<Emphasis Type="Italic">Pan troglodytes</Emphasis>)

We introduced a new technique to investigate the development of scribbling in very young infants. We tested three infant chimpanzees to compare the developmental processes of scribbling between humans and chimpanzees. While human infants start to scribble on paper at around the age of 18 months, our 13- to 23-month-old infant chimpanzees had never been observed scribbling prior to this study. We used a notebook computer with a touch-sensitive screen. This apparatus was able to record the location of the subjects touches on the screen. Each touch generated a fingertip-sized dot at the corresponding on-screen location. During spontaneous interactions with this apparatus, all three infants and two mother chimpanzees left scribbles with their fingers on the screen. The scribbles contained not only simple dots or short lines, but also curves and hook-like lines or loops, most of which were observed in the instrumental drawings of adult chimpanzees. The results suggest that perceptual-motor control for finger drawing develops in infant chimpanzees. Two of the infants performed their first scribble with a marker on paper at the age of 20–23 months. Just prior to this, they showed a rapid increase in combinatory manipulation of objects. These findings suggest that the development of combinatory manipulation of objects as well as that of perceptual-motor control may be necessary for the emergence of instrumental drawing on paper.     

Play for Success: An intervention to boost object exploration in infants from low-income households

Infants from low-income households typically spend less time exploring objects and use less mature strategies when they do explore compared to their higher-income peers (e.g., Clearfield et al., 2014). The current study tested a novel intervention designed to boost early object exploration in infants from low-income households. The intervention, called Play for Success, was administered through the Early Head Start home visiting program, and asked all infants to explore a toy with a caregiver for 10 min a day every day for two weeks. Forty-two 6- to 10-month-old infants were randomly assigned to one of three intervention groups: Social (unstructured direction), Teach Two (simple structured direction), or Teach Many (complex structured direction). Infants’ exploratory behaviors were tested three times: before the intervention, immediately following, and again four weeks later. The results demonstrated that only infants in Teach 2 maintained their level of exploration at both the post-test and 4 weeks later while infants in the other groups showed significant decreases in exploration over time. These results suggest that Play for Success is a promising new intervention, but only in the condition that included repeated simple structured direction.     

Role of mothers in the acquisition of tool-use behaviours by captive infant chimpanzees

This article explores the maternal role in the acquisition of tool-use behaviours by infant chimpanzees (Pan troglodytes). A honey-fishing task, simulating ant/termite fishing found in the wild, was introduced to three dyads of experienced mother and naïve infant chimpanzees. Four fishing sites and eight sets of 20 objects to be used as tools, not all appropriate, were available. Two of the mothers constantly performed the task, using primarily two kinds of tools; the three infants observed them. The infants, regardless of the amount of time spent observing, successfully performed the task around the age of 20–22 months, which is earlier than has been recorded in the wild. Two of the infants used the same types of tools that the adults predominantly used, suggesting that tool selectivity is transmitted. The results also show that adults are tolerant of infants, even if unrelated; infants were sometimes permitted to lick the tools, or were given the tools, usually without honey, as well as permitted to observe the adult performances closely.Electronic Supplementary Material Supplementary material is available in the online version of this article at     

Early perception-action coupling: eye movements and the development of object perception

We investigated the scanning strategies used by 2- to 3.5-month-old infants when viewing partly occluded object displays. Eye movements were recorded with a corneal reflection system as the infants observed stimuli depicting two rod parts above and below an occluding box. Stimulus parameters were chosen on the basis of past research demonstrating the importance of motion, occluder width, and edge alignment to perception of object unity. Results indicated that the infants tailored scanning to display characteristics, engaging in more extensive scanning when unity perception was challenged by a wide occluder or misaligned edges. In addition, older infants tended to scan the lower parts of the displays more frequently than did younger infants. Exploration of individual differences, however, revealed marked contrasts in specific scanning styles across infants. The findings are consistent with views of perceptual development stressing the importance of information processing skills and self-directed action to the acquisition of object knowledge.     

Milestones in the development of infant numeracy

This article deals with the development of numeracy among young children of the four to seven year age group. The research investigation described had two aims: to see how early numeracy develops in children of different ages; and to see whether there are fixed points which might serve as milestones in the development of infant numeracy. The results of this investigation involving 96 children indicate a strong development of numeracy skills during this period. With reference to the literature, it is also shown that certain items of a test previously developed for this purpose may be taken as core items that do indeed represent milestones in the development of infant numeracy.     

Ontogenetic Emergence of Cognitive Reference Comprehension

Prelinguistic cognitive reference comprehension is foundational to language acquisition and higher cognitive functions. However, its ontogenetic origins in the first year of life are currently not well understood. The current study pitted cognitivist against social interactionist views. We worked with infants monthly from 10 to 13 months of age and observed their behavioral search during a reference comprehension task. Our goal was to first establish the age at which infants begin to cognitively expect an occluded object in one of two locations following a communicative pointing cue. We then tested whether infants' cognitive referential expectations would prospectively predict social interaction skills and experiences (as assessed by spontaneous infant and parent pointing) or, conversely, be predicted by social interaction skills and experiences. Results revealed a linear increase in cognitive reference comprehension, with clear above chance performance, individual stability in month-to-month correlations, and a synchronous correlation to referential pointing all emerging at 12 months but not earlier. Regarding developmental predictions, infants' cognitive referential expectations were not predictive of social interaction skills and experiences; on the contrary, they were predicted by social interaction skills and experiences. Findings suggest that a nonverbal cognitive understanding of reference to occluded entities is neither early emerging, hard wired, nor causal to infants' or caregivers' referential pointing. Instead, this foundational skill is predicted by earlier social interaction. Findings are consistent with the view that cognitive reference comprehension develops via a social construction process in the first year of life.     

Reasoning about a hidden object after a delay: evidence for robust representations in 5-month-old infants

The present research examined two alternative interpretations of violation-of-expectation findings that young infants can represent hidden objects. One interpretation is that, when watching an event in which an object becomes hidden behind another object, infants form a prediction about the event's outcome while both objects are still visible, and then check whether this prediction was accurate. The other interpretation is that infants' initial representations of hidden objects are weak and short-lived and as such sufficient for success in most violation-of-expectation tasks (as objects are typically hidden for only a few seconds at a time), but not more challenging tasks. Five-month-old infants succeeded in reasoning about the interaction of a visible and a hidden object even though (1) the two objects were never simultaneously visible, and (2) a 3- or 4-min delay preceded the test trials. These results provide evidence for robust representations of hidden objects in young infants.     

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.     

Object individuation and labelling in 6-month-old infants

The ability to determine how many objects are involved in physical events is fundamental for reasoning about the world that surrounds us. Previous studies suggest that infants can fail to individuate objects in ambiguous occlusion events until their first birthday and that learning words for the objects may play a crucial role in the development of this ability. The present eye-tracking study tested whether the classical object individuation experiments underestimate young infants’ ability to individuate objects and the role word learning plays in this process. Three groups of 6-month-old infants (N = 72) saw two opaque boxes side by side on the eye-tracker screen so that the content of the boxes was not visible. During a familiarization phase, two visually identical objects emerged sequentially from one box and two visually different objects from the other box. For one group of infants the familiarization was silent (Visual Only condition). For a second group of infants the objects were accompanied with nonsense words so that objects’ shape and linguistic labels indicated the same number of objects in the two boxes (Visual & Language condition). For the third group of infants, objects’ shape and linguistic labels were in conflict (Visual vs. Language condition). Following the familiarization, it was revealed that both boxes contained the same number of objects (e.g. one or two). In the Visual Only condition, infants looked longer to the box with incorrect number of objects at test, showing that they could individuate objects using visual cues alone. In the Visual & Language condition infants showed the same looking pattern. However, in the Visual vs Language condition infants looked longer to the box with incorrect number of objects according to linguistic labels. The results show that infants can individuate objects in a complex object individuation paradigm considerably earlier than previously thought and that linguistic cues enforce their own preference in object individuation. The results are consistent with the idea that when language and visual information are in conflict, language can exert an influence on how young infants reason about the visual world.     

Changing patterns of infant behavior and mother–infant interaction: Intra- and interindividual variability

Mother–infant dyads were observed weekly at their homes for a 15-month period. In this way longitudinal data about the infants’ crying, fretting/fussing, smiling and different types of physical contact with the mother were collected. The subject of this study concerns the variability and stability in macroscopic patterns of associations between these behaviors. Different types of associations were found between the behaviors, and most of them changed considerably as the infant developed. Individual differences in the nature of the associations and in the changes they underwent over time predominated, but in a limited number of cases the infants shared the same developmental trajectories of behavioral associations. The results show how the use of intensive time series designs can be advantageous in clarifying issues of long-term variability and stability in human behavior. They also support the notion of changing patterns of behavior being a normal feature of early development.     

Developmental stimulation in child care centers contributes to young infants’ cognitive development

This study examined whether the quality of caregiver behavior in child care centers contributes to infant cognitive development at 9 months of age. Sixty-four infants (34 boys) were observed with their primary caregivers in child care centers at 3, 6, and 9 months of age. Caregiver behavior was rated for sensitivity and for stimulation of infant development during one-to-one caregiving interactions. Infant cognitive development was assessed using the Bayley Scales of Infant Development-II (Mental Development Index). Higher levels of developmental stimulation in the centers predicted higher levels of infant cognitive development at 9 months, beyond infant cognitive development at 3 months (just before entering child care), parental education, and maternal sensitivity. The results suggest that even small increases in developmental stimulation provided in child care centers in the first year of life may foster infants’ cognitive development.     

Postnatal depression and infant cognitive and motor development in the second postnatal year: The impact of depression chronicity and infant gender

A large body of literature has investigated the effects of postnatal depression on infant development. However, the particular circumstances in which depression is associated with adverse effects remain unresolved. Factors, such as the nature of depression (e.g., duration and severity) and the context with respect to other risk and protective factors (e.g., socioeconomic status and child gender) have been suggested as moderators of the effects of postnatal depression on infant outcomes. This study examined the impact of brief and chronic depression in a non-poverty sample of 112 mothers and their infants. Infant language development was assessed at 12 months, and at 15 months the Bayley Scales of Infant Development-II were administered. Chronic maternal depression, lasting throughout the first 12 months postpartum and beyond, was associated with lower infant cognitive and psychomotor development, with the effects being similar for boys and girls, while brief depression did not significantly impact the infant performance. Language development and infant behavior during testing were equivalent across the groups. The relatively high rates of motor development delay associated with chronic maternal depression found in this study are discussed along with the methodological issues and models of cumulative risk.