The emergence and development of reaching in infancy

Open Access
Author:
Lee, Mei-Hua
Graduate Program:
Kinesiology
Degree:
Doctor of Philosophy
Document Type:
Dissertation
Date of Defense:
March 17, 2011
Committee Members:
  • Karl Maxim Newell, Dissertation Advisor
  • Karl Maxim Newell, Committee Chair
  • John Henry Challis, Committee Member
  • Rick Owen Gilmore, Committee Member
  • Cynthia Bartok, Committee Member
Keywords:
  • visual feedback
  • infancy
  • Reaching
  • auditory feedback
Abstract:
The development of reaching movements is influenced by the interactions among the organism, task, and environmental constraints (Kawai, Savelsbergh, & Wimmers, 1999; Pick & Carman, 1994; Newell, 1986; Thelen; 1981). This dissertation addresses the general issue of the development in infancy of goal-directed arm movements under the influence of different sources of informational constraints. More specifically, the main focus was to investigate the role of environmental constraints including object properties, visual and audition feedback of the arm trajectory on the development of prehension during infancy. In Experiment 1, it was found that as infant age increased (10 – 14 weeks) through the phases of object-oriented movements, the distinguishing feature was that there was a decrease in movement jerk (when normalized to a dimensionless quantity), which reflects the increasing ability to adaptively modulate arm movements. This change in the dynamic characteristics of the object-oriented arm movements precedes the onset of goal-directed reaching movements and is hypothesised to reflect a critical variable in the infant developmental process of learning to reach in prehension. In Experiment 2, the influence of auditory feedback on the development of reaching movements in infancy was investigated at 10-14 weeks of age. The results showed that before the onset of reaching, the amplitude of the arm movement increased when the auditory feedback was provided. Also, at the point of reaching onset, the number of reaches increased when the auditory feedback was presented. Together, these results showed that before the onset of reaching, infants are able to use auditory feedback to explore the possibilities for action, and that subsequently the primitive form of these object-oriented arm movements is developed into more skilled and goal-directed reaching movements. In Experiment 3, we addressed the question of whether the development of prehension was influenced by the visual information of the hand trajectory and object properties at reach onset, 6 mo and 1 yr of age. It was found that age of onset of reaching for an object was earlier when the visual feedback of the hand trajectory was available. However, the effect of the visual feedback of the hand trajectory diminished after reach onset; there were no significant difference in terms of movement speed and smoothness at 6 mo and 1 yr of age. Infants also reached for the larger object earlier and with higher velocity than for the smaller object. Collectively, these results reveal the distinct roles of visual information of the hand trajectory and object property on the development of prehension during the infancy. In sum, the results of the experiments highlight the importance of exploratory behavior in early infancy and how exploratory behavior prior to the onset of reaching movements can be channeled through the vision and auditory information feedback. These findings are consistent with the perspective that the development of motor skill is influenced by the interactions among the organism, task and environment constraints. The weightings of the constraints as boundary conditions change at a certain developmental time in the emergence and mastering of the movement patterns.