The social cognition and perception-action literatures are largely separate, both conceptually and empirically. However, both areas of research emphasize infants' emerging abilities to use available information-social and perceptual information, respectively-for making decisions about action. Borrowing methods from both research traditions, this study examined whether 18-month-old infants incorporate both social and perceptual information in their motor decisions. The infants' task was to determine whether to walk down slopes of varying risk levels as their mothers encouraged or discouraged walking. First, a psychophysical procedure was used to determine slopes that were safe, borderline, and risky for individual infants. Next, during a series of test trials, infants received mothers' advice about whether to walk. Infants used social information selectively: They ignored encouraging advice to walk down risky slopes and discouraging advice to avoid safe slopes, but they deferred to mothers' advice at borderline slopes. Findings indicate that 18-month-old infants correctly weigh competing sources of information when making decisions about motor action and that they rely on social information only when perceptual information is inadequate or uncertain. Two sources of information are available to infants for making decisions about action: perceptual information generated by infants' own exploratory movements and social information offered by infants' parents and other people. An eager infant poised at the top of the stairs as mother screams "No!," a timid infant who is encouraged to attempt the daunting playground slide, a crawling infant whose parent's silence conveys that it is okay to roam, and a beginning walker reluctant to take steps into mother's open arms must decide whether to descend, slide, crawl, and walk on the basis of the available perceptual and social information.Sometimes perceptual and social cues are concordant, offering redundant information that specifies the way to act (e.g., when parents nod toward an inviting toy or say "No, no" toward a menacing dog). Other times, perceptual and social information are at odds, specifying opposing courses of action (e.g., when parents warn their toddlers to stay away from an empty street or encourage their infants to crawl onto the unfamiliar surface of a sandy beach). Discordant perceptual and social information is especially interesting because infants confront an interpretive challenge: They must decide how to weigh and integrate competing sources of information. In such situations, infants might assign priority to social information and defer to mothers' advice, regardless of their own perceptual assessment of the situation. Alternatively, infants might rely on perceptual information and ignore their mothers' social messages. A third possibility is that infants assess social and perceptual cues on a case-by-case basis, relying selectively on social information when perceptual cues leave them uncertain about how to act. On this last account, infan...

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° 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.

Affordances-possibilities for action-are constrained by the match between actors and their environments. For motor decisions to be adaptive, affordances must be detected accurately. Three experiments examined the correspondence between motor decisions and affordances as participants reached through apertures of varying size. A psychophysical procedure was used to estimate an affordance threshold for each participant (smallest aperture they could fit their hand through on 50% of trials), and motor decisions were assessed relative to affordance thresholds. Experiment 1 showed that participants scale motor decisions to hand size, and motor decisions and affordance thresholds are reliable over two blocked protocols. Experiment 2 examined the effects of habitual practice: Motor decisions were equally accurate when reaching with the more practiced dominant hand and less practiced non-dominant hand. Experiment 3 showed that participants recalibrate motor decisions to take changing body dimensions into account: Motor decisions while wearing a hand-enlarging prosthesis were similar to motor decisions without the prosthesis when data were normalized to affordance thresholds. Across experiments, errors in decisions to reach through too-small apertures were likely due to low penalty for error. Keywordsaffordance; aperture; perception-action; psychophysics; reaching Possibilities for motor action-or what Gibson (1979) termed affordances-depend on the match between environmental conditions and actors' physical characteristics (e.g., Adolph & Berger, 2006). The affordance concept is central to motor control because adaptive motor decisions must be based on actual possibilities for action (Gibson, 1979;Warren, 1984). On a perception-action account of motor control, observers must perceive affordances (or lack of them) with sufficient accuracy to select the appropriate movements and modify them appropriately to suit the constraints of the current situation. The perceptual problem is not trivial. Affordances can change from moment to moment due to variations in the environment and in actors' bodies and propensities. Perceiving affordances is an ongoing process of gauging the relationship between the current status of the body and the relevant environmental properties. Navigating through AperturesA good example of coping with changing affordances is navigating various body parts through apertures. Fitting through an aperture-steering a path along a crowded sidewalk, squeezing between seats in a lecture hall, reaching the hand into the slot of a vending machine-is constrained by the dimensions and shape of the relevant body parts relative to the dimensions and shape of the opening. Visual guidance is critical for comparing body dimensions to the size of the opening, and for determining how best to orient the relevant body parts relative to *shaziela@nyu.edu. NIH Public Access NIH-PA Author ManuscriptNIH-PA Author Manuscript NIH-PA Author Manuscript its shape. Indeed, even frogs and toads use visual information for guiding...

Perceiving possibilities for action—affordances—requires sensitivity, accuracy, and consistency. In the current study, we tested children of different ages (16-month-olds to 7-year-olds) and adults to examine the development of affordance perception for reaching through openings of various sizes. Using a psychophysical procedure, we estimated individual affordance functions to characterize participants' actual ability to fit their hand through openings and individual decision functions to characterize attempts to reach. Decisions were less accurate in younger children (16-month-olds to 5-year-olds); they were more likely to attempt impossible openings and to touch openings prior to refusing, suggesting a slow developmental trend in learning to perceive affordances for fitting through openings. However, analyses of multiple outcome measures revealed that the youngest participants were equally consistent in their decision making as the oldest ones and that every age group showed sensitivity to changes in the environment by scaling their attempts to opening size.