Task-specific adaptations of postural sway in sitting infants

Developmental Changes in How Head Orientation Structures Infants' Visual Attention

Most studies of developing visual attention are conducted using screen-based tasks in which infants move their eyes to select where to look. However, real-world visual exploration entails active movements of both eyes and head to bring relevant areas in view. Thus, relatively little is known about how infants coordinate their eyes and heads to structure their visual experiences. Infants were tested every 3 months from 9 to 24 months while they played with their caregiver and three toys while sitting in a highchair at a table. Infants wore a head-mounted eye tracker that measured eye movement toward each of the visual targets (caregiver's face and toys) and how targets were oriented within the head-centered field of view (FOV). With age, infants increasingly aligned novel toys in the center of their head-centered FOV at the expense of their caregiver's face. Both faces and toys were better centered in view during longer looking events, suggesting that infants of all ages aligned their eyes and head to sustain attention. The bias in infants' head-centered FOV could not be accounted for by manual action: Held toys were more poorly centered compared with non-held toys. We discuss developmental factors-attentional, motoric, cognitive, and social-that may explain why infants increasingly adopted biased viewpoints with age.

Focused attention as a new sitter: How do infants balance it all?

This study investigated the impact of postural control on infants' Focused Attention (FA). Study 1 examined whether and how sitting independently versus with support impacted 6- to 8-month-old infants' ability to focus attention during object exploration. FA measures did not depend on support condition. However, sitting experience was significantly negatively correlated with FA measures in the supported condition, suggesting that infants with more sitting experience performed fewer exploratory movements, possibly due to faster information processing ability compared to infants with less sitting experience. These unexpected findings prompted an exploration of more subtle looking behaviors during FA in Study 2-a case study of three infants who wore a head-mounted eye-tracker during an FA task. The ability to rapidly shift visual attention was key to gathering environmental information useful for problem solving-an interpretation that is supported by prior findings of the relationship between fast looks and faster information processing.

Controlling posture to see the world: The integration of visual task demands and postural sway in sitting and standing infants

Our ability to integrate posture with visually demanding tasks is a critical aspect of motor behavior flexibility. When looking at a small object, excessive body movements impair an individual's ability to visually attend to the object. To overcome this problem, we adjust our postural sway to successfully focus on the object. The goal of the current study was to assess whether infants also adjust postural sway when engaged in a challenging visual task. The participants, 19 independently sitting infants (Sitters) and 21 newly independently standing infants (Standers), sat or stood on a force plate while viewing differently sized images displayed on a monitor (smaller images: 8 × 6.5 cm or 3 × 3 cm; larger images: 13 × 16 cm or 13 × 13 cm). Regardless of image size, Standers were less stable than Sitters with larger sway areas and faster sway velocities. Both Sitters and Standers adjusted sway area but not sway velocity, based on image size. Sitters and Standers differed in how they controlled sway dynamics. Standers but not Sitters altered sway dynamics based on image size. Overall, infants used posture-specific adaptive control strategies to make fine-grained adjustments based on image size. The development of the ability to integrate posture with a visually demanding task further emphasizes the capability of advanced complex motor behaviors during infancy, enabling infants to flexibly attend to important aspects of their environment at different postural positions.

Multiple patterns of infant rolling in limb coordination and ground contact pressure

Infants acquire the ability to roll over from the supine to the prone position, which requires body coordination of multiple degrees of freedom under dynamic interactions with the ground. Although previous studies on infant rolling observed kinematic characteristics, little is known about the kinetic characteristics of body segments in contact with the surface. We measured the ground contact pressure under the arms, legs, head, and proximal body segments using a pressure mat and their displacements using a three-dimensional motion capture system. The data obtained from 17 infants aged 9-10 months indicated that most of them showed 2-4 of 6 highly observed movement patterns, including 1 axial rolling, 2 spinal flexion, and 3 shoulder girdle leading patterns. The arms and legs had small contributions to the ground contact pressure in the axial rolling and spinal flexion patterns. The ipsilateral leg in relation to the rolling direction was involved in supporting the body weight in only 1 shoulder girdle leading pattern. The contralateral leg showed large peak pressure to push on the floor before rolling in 3 shoulder girdle leading patterns. The results indicate that infants can produce multiple rolling-over patterns with different strategies to coordinate their body segments and interact with the floor. The results of the analysis of the movement patterns further suggest that few patterns correspond to those reported in adults. This implies that infants generate unique motor patterns by taking into account their own biomechanical constraints.