Doctoral Dissertations

Date of Award

8-2024

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Psychology

Major Professor

Daniela Corbetta

Committee Members

Daniela Corbetta, Aaron T. Buss, Caglar A. Tas, Jared M. Porter

Abstract

The onset of reaching during infancy, a critical milestone influenced by developmental experiences, is the focal point of this research study. The individual differences in these experiences may significantly impact when infants achieve this milestone. Traditionally, the study of reaching onset has focused on the interplay between the visual and motor systems, with researchers often overlooking the motor system. However, a detailed analysis of motor behaviors is warranted, given the extensive research on the visual-motor system. This study, therefore, not only fills a gap in the existing research but also makes a significant contribution to the developmental psychology field and child development by shedding new light on the motor system's role in reaching onset. The current study analyzes six infants' behavioral and kinematic changes around the onset of reaching. Further, the infants were categorized into two groups based on age at reach-onset: early and late reachers. Using observational data and based on a literature review, movement activities, such as mouth and face contacts and midline hand clasping, were identified. Frequency, duration, and kinematics were analyzed to determine infants' developmental changes around the week of reach onset. Results show that differences between early and late reachers in attaining this milestone are linked to overall activity and transitions from non-reaching to reaching behaviors. Early reachers displayed increasing movement events as they approached the time of reach onset, and these events decreased following when they reached. On the contrary, late reachers displayed minimal movement events until the onset of reaching, at which time they increased their events significantly until the last week of observation. These findings indicate that early reachers are more active and must dampen down their activity to reach successfully. Alternatively, late reachers require a ramping up in their activity levels once they have developed reaching.

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