Assessing the Impact of Movement Consequences on the Development of Early Reaching in Infancy.

Prior research on infant reaching has shown that providing infants with repeated opportunities to reach for objects aids the emergence and progression of reaching behavior. This study investigated the effect of movement consequences on the process of learning to reach in pre-reaching infants. Thirty-five infants aged 2.9 months at the onset of the study were randomly assigned to 1 of 3 groups. Two groups received a 14-day intervention to distinct reaching tasks: (1) in a contingent group, a toy target moved and sounded upon contact only, and (2) in a continuous group, the toy moved and sounded continuously, independent of hand-toy contact. A third control group did not receive any intervention; this group's performance was assessed only on 2 days at a 15-day interval. Results revealed that infants in the contingent group made the most progress over time compared to the two other groups. Infants in this group made significantly more overall contacts with the sounding/moving toy, and they increased their rate of visually attended target contacts relative to non-visually attended target contacts compared to the continuous and control groups. Infants in the continuous group did not differ from the control group on the number of hand-toy contacts nor did they show a change in visually attended target versus non-visually attended target contacts ratio over time. However, they did show an increase in movement speed, presumably in an attempt to attain the moving toy. These findings highlight the importance of contingent movement consequences as a critical reinforcer for the selection of action and motor learning in early development. Through repeated opportunities to explore movement consequences, infants discover and select movements that are most successful to the task-at-hand. This study further demonstrates that distinct sensory-motor experiences can have a significant impact on developmental trajectories and can influence the skills young infants will discover through their interactions with their surroundings.

Bare fingers, but no obvious influence of "prickly" Velcro! In the absence of parents' encouragement, it is not clear that "sticky mittens" provide an advantage to the process of learning to reach.

In their critique of our mittens study, Needham et al. (2015. Infant Behavior and Development) describe our findings as "surprising." Further; they suggest that babies in our "sticky mittens" condition may have been discouraged from reaching because, in our study, infants may have touched "prickly" Velcro with their bare fingers. In this response, we present data analyses that do not support the interpretation that finger contact with our Velcroed toy surfaces was associated with poor reaching performance in our "sticky" mittens group. We also clarify that our toys were mainly covered with "non-prickly" Velcro. To explain discrepancies between studies, we restate the original intent of our study and reasons for our methodological modifications. We point to confounds and lack of critical control conditions in the Needham et al. studies, which prevent the making of firm inferences about the effectiveness of the "sticky mittens experience" on the learning to reach process. We also present additional analyses on our "sticky" mittens group showing that the increasing rate of finger touch on the toy leads to greater reaching performance while the rate of toy sticking to the mittens does not. We discuss the importance of sensory-motor experience on the development of learning to reach in infancy and conclude that our results are not surprising.

Learning to reach with "sticky" or "non-sticky" mittens: a tale of developmental trajectories.

The effects of "sticky" and "non-sticky" mittens upon the progression of intentional reaching were examined over 16-day training in 24 non-reaching infants aged 2 months and 21 days. Thirteen age-matched controls did not receive training. Both mittens groups progressed over time; however, by day 16, only the "non-sticky" group made significantly more toy contacts than the controls when looking at the toy. Infants in the "non-sticky" group also directed their looking at the toy more than infants in the "sticky" mittens group. These results support the interpretation that repeated task exposure, with active, reaching-specific experience, was more likely to enhance the formation of object-directed behaviors than with the added provision of grasping simulation via "sticky mittens."

Mapping the feel of the arm with the sight of the object: on the embodied origins of infant reaching.

For decades, the emergence and progression of infant reaching was assumed to be largely under the control of vision. More recently, however, the guiding role of vision in the emergence of reaching has been downplayed. Studies found that young infants can reach in the dark without seeing their hand and that corrections in infants' initial hand trajectories are not the result of visual guidance of the hand, but rather the product of poor movement speed calibration to the goal. As a result, it has been proposed that learning to reach is an embodied process requiring infants to explore proprioceptively different movement solutions, before they can accurately map their actions onto the intended goal. Such an account, however, could still assume a preponderant (or prospective) role of vision, where the movement is being monitored with the scope of approximating a future goal-location defined visually. At reach onset, it is unknown if infants map their action onto their vision, vision onto their action, or both. To examine how infants learn to map the feel of their hand with the sight of the object, we tracked the object-directed looking behavior (via eye-tracking) of three infants followed weekly over an 11-week period throughout the transition to reaching. We also examined where they contacted the object. We find that with some objects, infants do not learn to align their reach to where they look, but rather learn to align their look to where they reach. We propose that the emergence of reaching is the product of a deeply embodied process, in which infants first learn how to direct their movement in space using proprioceptive and haptic feedback from self-produced movement contingencies with the environment. As they do so, they learn to map visual attention onto these bodily centered experiences, not the reverse. We suggest that this early visuo-motor mapping is critical for the formation of visually-elicited, prospective movement control.

Infant Eye-tracking in the Context of Goal-Directed Actions.

This paper presents two methods that we applied to our research to record infant gaze in the context of goal-oriented actions using different eye-tracking devices: head-mounted and remote eye-tracking. For each type of eye-tracking system, we discuss their advantages and disadvantages, we describe the particular experimental setups we used to study infant looking and reaching, explain how we were able to use and synchronize these systems with other sources of data collection (video recordings and motion capture) in order to analyze gaze and movements directed toward 3D objects within a common time frame. Finally, for each method, we briefly present some results from our studies to illustrate the different levels of analyses that may be carried out using these different types of eye-tracking devices. These examples aim to highlight some of the novel questions that may be addressed using eye-tracking in the context of goal-directed actions.

Proactive stability control while carrying loads and negotiating an elevated surface.

In this study, proactive stability control while handling loads and negotiating an elevated surface was examined. Ten young healthy males completed two gait-mode conditions--level walking and negotiating a raised surface. Load-handling conditions were: no load, empty box (reduced visual information), and loaded box (reduced visual information combined with increased inertial load). The lower limb trajectory in the sagittal plane was not modified as a function of reduced visual information or increased inertial load. The step width decreased while stepping over the surface and carrying the loaded box. The trunk pitch angle was biased backwards for both the empty box and the loaded box. When carrying the empty box and negotiating the surface, the trunk pitch range of motion (ROM) increased which may have been a strategy to increase visual exteroceptive information. As increased net trunk pitch could destabilize the system, concurrent stabilizing strategies--decreased gait velocity and reduced net trunk roll velocity--were observed. To meet the equilibrium goals when carrying the loaded box, the trunk pitch ROM and net pitch velocity were reduced during both level walking and surface accommodation. Trunk roll ROM was reduced when carrying the load and negotiating the surface. This study extends our knowledge regarding whole body coordination strategies during anticipatory locomotor adaptations.