Carry on: spontaneous object carrying in 13-month-old crawling and walking infants

Carrying objects requires coordination of manual action and locomotion. This study investigated spontaneous carrying in 24 walkers who were 13 months old and 26 crawlers who were 13 months old during 1-hr, naturalistic observations in the infants' homes. Carrying was more common in walkers, but crawlers also carried objects. Typically, walkers carried objects in their hands, whereas crawlers multitasked by using their hands simultaneously for holding objects and supporting their bodies. Locomotor experience predicted frequency of carrying in both groups, suggesting that experienced crawlers and walkers perceive their increased abilities to handle objects while in motion. Despite additional biomechanical constraints imposed by holding an object, carrying may actually improve upright balance: Crawlers rarely fell while carrying an object, and walkers were more likely to fall without an object in hand than while carrying. Thus, without incurring an additional risk of falling, spontaneous carrying may provide infants with new avenues for combining locomotor and manual skills and for interacting with their environments.     

The role of crawling and walking experience in infant spatial memory

This research explored infants' use of place learning and cue learning in a locomotor task across the transition from crawling to walking. Novice and expert crawling and walking infants were observed in a novel locomotor task-finding a hidden goal location in a large space. In Experiment 1, infants were tested with distal landmarks. Infants with fewer than 6 weeks of experience, either crawling or walking, could not find the goal location. All infants with more locomotor experience were more successful. Learning did not transfer across the transition to walking. In Experiment 2, novice and expert crawlers and walkers were tested with a direct landmark. Again, novice crawlers and walkers with fewer than 6 weeks of experience could not find the goal, whereas those with more experience could. Taken together, these findings suggest that infants' spatial learning is inextricably linked to mode of locomotion.     

Locomotor experience and use of social information are posture specific

The authors examined the effects of locomotor experience on infants' perceptual judgments in a potentially risky situation--descending steep and shallow slopes--while manipulating social incentives to determine where perceptual judgments are most malleable. Twelve-month-old experienced crawlers and novice walkers were tested on an adjustable sloping walkway as their mothers encouraged and discouraged descent. A psychophysical procedure was used to estimate infants' ability to crawl/walk down slopes, followed by test trials in which mothers encouraged and discouraged infants to crawl/walk down. Both locomotor experience and social incentives affected perceptual judgments. In the encourage condition, crawlers only attempted safe slopes within their abilities, but walkers repeatedly attempted impossibly risky slopes, replicating previous work. The discourage condition showed where judgments are most malleable. When mothers provided negative social incentives, crawlers occasionally avoided safe slopes, and walkers occasionally avoided the most extreme 50 degrees increment, although they attempted to walk on more than half the trials. Findings indicate that both locomotor experience and social incentives play key roles in adaptive responding, but the benefits are specific to the posture that infants use for balance and locomotion.     

Detection of the relevant type of locomotion in infancy: crawlers versus walkers

Human infants show a preference for individuals who are similar to them. Using point-light displays of human walkers and crawlers as stimuli, we examined whether infants' preference for the motions of crawling and walking changes between, before, and after the onset of bipedal walking. The results show that crawling and walking infants prefer the types of locomotion that are similar to their own, respectively. These indicate that the infants detect the similarities between the motions they performed and they observed, which provides the behavioral evidence that the production of a particular motion is connected to its perception in infancy.     

Detection of the traversability of surfaces by crawling and walking infants

In four studies we investigated the perception of the affordance for traversal of a supporting surface. The surface presented was either rigid or deformable, and this property was specified either optically, haptically, or both. In Experiment 1A, crawling and walking infants were presented with two surfaces in succession: a standard surface that both looked and felt rigid and a deforming surface that both looked and felt nonrigid. Latency to initiate locomotion, duration of visual and haptic exploration, and displacement activity were coded from videotapes. Compared with the standard, the deforming surface elicited longer latency, more exploratory behavior, and more displacement in walkers, but not in crawlers, suggesting that typical mode of locomotion influences perceived traversability. These findings were replicated in Experiment 1B, in which the infant was presented with a dual walkway, forcing a choice between the two surfaces. Experiments 2, 3A and B, and 4A and B investigated the use of optical and haptic information in detecting traversability of rigid and nonrigid surfaces. Patterns of exploration varied with the information presented and differed for crawlers and walkers in the case of a deformable surface, as an affordance theory would predict.     

The organization of exploratory behaviors in infant locomotor planning

How do infants plan and guide locomotion under challenging conditions? This experiment investigated the real‐time process of visual and haptic exploration in 14‐month‐old infants as they decided whether and how to walk over challenging terrain – a series of bridges varying in width. Infants’ direction of gaze was recorded with a head‐mounted eye tracker and their haptic exploration and locomotor actions were captured on video. Infants’ exploration was an organized, efficient sequence of visual, haptic, and locomotor behaviors. They used visual exploration from a distance as an initial assessment on nearly every bridge. Visual information subsequently prompted gait modifications while approaching narrow bridges and haptic exploration at the edge of the bridge. Results confirm predictions about the sequential, ramping‐up process of exploration and the distinct roles of vision and touch. Exploration, however, was not a guarantee of adaptive decisions. With walking experience, exploratory behaviors became increasingly efficient and infants were better able to interpret the resulting perceptual information in terms of whether it was safe to walk.     

Differences in caregiver behaviors of infants at-risk for autism and typically developing infants from 9 to 15 months of age

During an object sharing paradigm, we compared infant-caregiver interactions between two groups: i) infants at high-risk (HR) for being diagnosed with Autism Spectrum Disorder (ASD) and ii) low-risk (LR) infants, observed at 9, 12, and 15 months of age. 16 HR infants (14 infants with an older sibling diagnosed with ASD and 2 preterm infants that received a diagnosis of ASD at 2 years) and 16 LR infants (typically developing infants without older siblings diagnosed with ASD) were included in the study. At each visit, infants played with objects in the presence of their caregivers as crawlers or walkers. Previously, we found that HR infants are less likely to share their object play with caregivers at walker ages. The present study found that caregivers of HR infants used greater directive bids including being more proximal to infants and using greater verbal and non-verbal bids to sustain their infant’s attention and to ensure their compliance during the task compared to caregivers of LR infants. Our study emphasizes the bidirectional and dynamic nature of infant-caregiver interactions. Our findings have implications for caregiver training programs that teach parents appropriate strategies to promote early social communication skills in at-risk infants.     

Crawling in and out of sleep

The goal of the study was to examine the link between motor attainments and sleep–wake regulation by comparing the sleep characteristics of infants who are crawling with the sleep of same‐age infants who have not yet acquired the locomotion milestone. The participants were 59 healthy 8‐month‐old infants with no developmental delays, who were recruited through well‐baby clinics and childcare centers. The measurements included objective sleep recordings (actigraphy), sleep questionnaire, and motor milestones checklist. The main finding was that the sleep of crawlers was more fragmented in comparison to the sleep of pre‐crawlers. While the findings of this report give support to the hypothesized link between sleep regulation and motor development, more studies are needed to clarify why crawling might provide a marker of nightwaking. In discussing the results, it is proposed that the association between fragmented sleep and crawling could be related to maturational, constitutional, and relational factors. Copyright © 2005 John Wiley & Sons, Ltd.     

Ages of young children who fall down stairs.

Different accident patterns were noted for children using walkers and not using walkers at the time of an accident. The children were divided into two locomotion groups, natural locomotion (384 children) and walker-aided locomotion (235 children), depending on the presence or absence of a walker during the fall down the stairs. A review of incidents reported by a sample of emergency rooms identified 619 falls down steps by children between 5 and 18 mo. old during the first 6 months of 1995. The age of the highest risk, as indicated by the frequency of falls down the stairs, for the walker-aided locomotion group was 8 mo. The age of highest risk for the natural locomotion group was 12 mo. Children who fall down the stairs, in or out of a walker, are victims of the same hazard, unprotected stairs. Home safety recommendations to reduce the risk of young children falling down the stairs are provided.     

Confidence and Eyewitness Identifications: The Cross‐Race Effect,Decision Time and Accuracy

Participants encountered same‐race and cross‐race faces at encoding, completed a series of line‐up identification tests and provided confidence ratings by using one of nine different confidence scales. Confidence was less well calibrated with identification accuracy when participants selected a cross‐race than a same‐race face because of overconfidence. By contrast, there was no cross‐race effect on confidence–accuracy calibration when participants responded ‘not present’. Whereas confidence was a very strong predictor of accuracy for fast identifications of a line‐up face, this was much less the case for slower decisions. Highly confident identifications showed a dramatic drop in accuracy from faster decisions to slower decisions, whereas there was little change in accuracy between faster and slower decisions for moderately confident or weakly confident identifications. Finally, we observed little influence of the format of the nine different confidence scales: numerical and verbal scales produced comparable calibration scores, as did scales with few or many points. Copyright © 2015 John Wiley & Sons, Ltd.     

One and Done? Optimal Decisions From Very Few Samples

In many learning or inference tasks human behavior approximates that of a Bayesian ideal observer, suggesting that, at some level, cognition can be described as Bayesian inference. However, a number of findings have highlighted an intriguing mismatch between human behavior and standard assumptions about optimality: People often appear to make decisions based on just one or a few samples from the appropriate posterior probability distribution, rather than using the full distribution. Although sampling‐based approximations are a common way to implement Bayesian inference, the very limited numbers of samples often used by humans seem insufficient to approximate the required probability distributions very accurately. Here, we consider this discrepancy in the broader framework of statistical decision theory, and ask: If people are making decisions based on samples—but as samples are costly—how many samples should people use to optimize their total expected or worst‐case reward over a large number of decisions? We find that under reasonable assumptions about the time costs of sampling, making many quick but locally suboptimal decisions based on very few samples may be the globally optimal strategy over long periods. These results help to reconcile a large body of work showing sampling‐based or probability matching behavior with the hypothesis that human cognition can be understood in Bayesian terms, and they suggest promising future directions for studies of resource‐constrained cognition.     

Do infants have a sense of numerosity? A p‐curve analysis of infant numerosity discrimination studies

Research demonstrating that infants discriminate between small (e.g., 1 vs. 3 dots) and large numerosities (e.g., 8 vs. 16 dots) is central to theories concerning the origins of human numerical abilities. To date, there has been no quantitative meta‐analysis of the infant numerical competency data. Here, we quantitatively synthesize the evidential value of the available literature on infant numerosity discrimination using a meta‐analytic tool called p‐curve. In p‐curve the distribution of available p‐values is analyzed to determine whether the published literature examining particular hypotheses contains evidential value. p‐curves demonstrated evidential value for the hypotheses that infants can discriminate between both small and large unimodal and cross‐modal numerosities. However, the analyses also revealed that the published data on infants’ ability to discriminate between large numerosities is less robust and statistically powered than the data on their ability to discriminate small numerosities. We argue there is a need for adequately powered replication studies to enable stronger inferences in order to use infant data to ground theories concerning the ontogenesis of numerical cognition.     

Twelve‐ to 14‐month‐old infants can predict single‐event probability with large set sizes

Previous research has revealed that infants can reason correctly about single‐event probabilities with small but not large set sizes ( Bonatti, 2008 ; Teglas et al., 2007 ). The current study asks whether infants can make predictions regarding single‐event probability with large set sizes using a novel procedure. Infants completed two trials: A preference trial to determine whether they preferred pink or black lollipops and a test trial where infants saw two jars, one containing mostly pink lollipops and another containing mostly black lollipops. The experimenter removed one occluded lollipop from each jar and placed them in two separate opaque cups. Seventy‐eight percent of infants searched in the cup that contained a lollipop from the jar with a higher proportion of their preferred color object, significantly better than chance. Thus infants can reason about single‐event probabilities with large set sizes in a choice paradigm, and contrary to most findings in the infant literature, the prediction task used here appears a more sensitive measure than the standard looking‐time task.     

Is this still called a dog? 18‐month‐olds' generalization of familiar labels to unusual objects

In two experiments the flexibility of 18‐month‐olds' extension of familiar object labels was investigated using the intermodal preferential looking paradigm. The first experiment tested whether infants consider intact and incomplete objects as equally acceptable referents for familiar labels. Infants looked equally long at the intact and incomplete objects whether or not a label was presented. In the second experiment, infants were requested to find the referent of a target word among an incomplete target and an intact distracter or an intact target and an incomplete distracter. The incomplete objects were missing a large or small part. Infants looked longer at the incomplete target, even when large or small parts were deleted. Taken together, these findings suggest that infants do not hold a strong shape bias when generalizing familiar words. Copyright © 2002 John Wiley & Sons, Ltd.     

Go naked: diapers affect infant walking

In light of cross‐cultural and experimental research highlighting effects of childrearing practices on infant motor skill, we asked whether wearing diapers, a seemingly innocuous childrearing practice, affects infant walking. Diapers introduce bulk between the legs, potentially exacerbating infants’ poor balance and wide stance. We show that walking is adversely affected by old‐fashioned cloth diapers, and that even modern disposable diapers – habitually worn by most infants in the sample – incur a cost relative to walking naked. Infants displayed less mature gait patterns and more missteps and falls while wearing diapers. Thus, infants’ own diapers constitute an ongoing biomechanical perturbation while learning to walk. Furthermore, shifts in diapering practices may have contributed to historical and cross‐cultural differences in infant walking.     

Coping with asymmetry: How infants and adults walk with one elongated leg

The stability of a system affects how it will handle a perturbation: The system may compensate for the perturbation or not. This study examined how 14-month-old infants—notoriously unstable walkers—and adults cope with a perturbation to walking. We attached a platform to one of participants’ shoes, forcing them to walk with one elongated leg. At first, the platform shoe caused both age groups to slow down and limp, and caused infants to misstep and fall. But after a few trials, infants altered their gait to compensate for the platform shoe whereas adults did not; infants recovered symmetrical gait whereas adults continued to limp. Apparently, adult walking was stable enough to cope with the perturbation, but infants risked falling if they did not compensate. Compensation depends on the interplay of multiple factors: The availability of a compensatory response, the cost of compensation, and the stability of the system being perturbed.     

Implications of statistical power for confidence intervals

The statistical power of a hypothesis test is closely related to the precision of the accompanying confidence interval. In the case of a z-test, the width of the confidence interval is a function of statistical power for the planned study. If minimum effect size is used in power analysis, the width of the confidence interval is the minimum effect size times a multiplicative factor φ. The index φ, or the precision-to-effect ratio, is a function of the computed statistical power. In the case of a t-test, statistical power affects the probability of achieving a certain width of confidence interval, which is equivalent to the probability of obtaining a certain value of φ. To consider estimate precision in conjunction with statistical power, we can choose a sample size to obtain a desired probability of achieving a short width conditional on the rejection of the null hypothesis.     

Riskier for me or for others? The role of domain and probability in self-other differences,in risky decision-making

Abstract

In social and economic interactions, people often decide differently for others, as against for themselves, under situations involving risks. This sometimes leads to conflicts or contradictions. Although previous studies have explored such contradictions, the findings have been inconsistent. To reconcile these inconsistencies, this paper investigates the role played by the different domains and probabilities in the self-other differences under risk. Two groups of participants completed a gambling task combining different domains (gain vs. loss) and probabilities (small vs. large). One group made decisions for others and the other group made decisions for themselves. The results revealed a four pattern of discrepancy: the ones who made decisions for others were less risk-seeking than those who made decisions for themselves over the small probability gains. This was reversed over the large probability gains. Conversely, the participants who made decisions for others were more risk-seeking than those who made decisions for themselves over the small probability losses. The results were reversed over the large probability losses. These results reconcile the contradictory findings of the previous studies and suggest the significant role played by contextual factors in such discrepancies.