Infants prospectively control reaching based on the difficulty of future actions: To what extent can infants’ multiple-step actions be explained by Fitts’ law?

Abstract

Prospective motor control, a key element of action planning, is the ability to adjust one's actions with respect to task demands and action goals in an anticipatory manner. The current study investigates whether 14-month-olds can prospectively control their reaching actions based on the difficulty of the subsequent action. We used a reach-to-place task, with difficulty of the placing action varied by goal size and goal distance. To target prospective motor control, we determined the kinematics of the prior reaching movements using a motion-tracking system. Peak velocity of the first movement unit of the reach served as indicator for prospective motor control. Both difficulty aspects (goal size and goal distance) affected prior reaching, suggesting that both these aspects of the subsequent action have an impact on the prior action. The smaller the goal size and the longer the distance to the goal, the slower infants were in the beginning of their reach toward the object. Additionally, we modeled movement times of both reaching and placing actions using a formulation of Fitts' law (as in heading). The model was significant for placement and reaching movement times. These findings suggest that 14-month-olds can plan their future actions and prospectively control their related movements with respect to future task difficulties. (PsycINFO Database Record

Two-step actions in infancy - the TWAIN model

“…Developing a model for two-step actions in infancy was motivated by four issues: First, while established speed-accuracy models, such as the ones by Fitts (1954) or Welford, Norris, and Shock (1969), have been applied to describe infants' actions (Gottwald et al, 2017;Zaal & Thelen, 2005), they were originally developed to describe adults' actions. During infancy, however, there is rapid development, both with respect to the actions that infants can perform and with respect to the accuracy of these actions (e.g., ).…”

“…Using models primarily from the adult literature might therefore not be suitable to fully understand action development or to investigate the nature of two-step actions before they are fully mastered. Second, while existing models have been used to describe two-step actions (Gottwald et al, 2017), they were originally developed for single actions, such as finger pointing. For richer understanding of the development of the more ecologically valid two-step actions performed by infants, it is important to develop models that also consider the two-step nature of actions.…”

“…(but see e.g., DeSantis, Harkins, Tronick, Kaplan, & Beeghly, 2011;Munakata, 1998), and specifically infants' actions (Berthier, 1996;Berthier & Keen, 2006;Gottwald, 2018;Gottwald et al, 2017;Zaal & Thelen, 2005) despite the rich possibilities of such an approach. Finally, existing modelling studies with infants have comparably low sample sizes -around 10 to infants per age group (e.g., Berthier & Keen, 2006;Zaal & Thelen, 2005).…”

“…Multiple-step actions are actions consisting of two or more sub-actions -for example, reach-to-place actions, which consist of the two sub-actions (1) reaching and (2) placing (cf. Gottwald et al, 2017). Based on Bernstein's conceptualization of action as goal-directed behavior with the goal as the center of action planning (Bernstein, 1996;Grafton & Hamilton, 2008) and in contrast to non-goal directed behavior, we can think of multiple-step actions as being to some extent planned before they are performed.…”

“…Similar results were shown for infants: Ten-month-olds perform their reach based on the parameters of the subsequent placing action (Claxton, Keen, & McCarty, 2003) and 14-montholds perform even the first part (i.e., the first movement unit; cf. von Hofsten, 1979Hofsten, , 1991 of their reach based on the parameters of the subsequent placing action (Gottwald et al, 2017).…”