Date of Award

8-2011

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Psychology

Major Professor

Daniela Corbetta

Committee Members

Gordon M. Burghardt, Jeffrey Fairbrother, Jenny Macfie, Greg Reynolds

Abstract

Previous studies found that providing infants with repeated opportunities for reaching improved the emergence and quality of the behavior, presumably via exploratory and selective processes (Bojczyk & Corbetta, 2004; Lobo et al., 2008). Here we further examined the effects of opportunities for reaching by exposing infants to multimodal objects that were activated either continuously by a hidden motor or contingently by hand-toy contact. We asked if such objects would motivate infants to try to reach for them even more than still and silent objects.

Forty-four pre-reaching infants were recruited within the week prior to turning three months of age and were seen for 16 consecutive days. Three groups received daily exposure to objects that either moved and made noise continuously (continuous), moved and made noise only on hand-object contact (contingent), or did not move or make noise when touched (repeated task exposure). A control group received no daily experience. On day 1, all infants were assessed in the laboratory to ensure they were not reaching. From days 2-15, an experimenter tested the repeated groups in the home. On day 16, all infants’ reaching was reassessed in our laboratory. Arm kinematics were recorded during laboratory visits. All testing was the same: infants were seated in an infant chair behind a table and an experimenter placed 1 toy on the table at midline for one minute. Infants received ten trials per day. We measured amount of intentional reaches, hand-toy distance, and peak movement speed.

Intentional reaching significantly increased for all repeated groups. Examination of infants that improved showed that the contingent group displayed a significantly higher gain in reaching over time relative to the repeated task exposure and continuous groups. Kinematic measures indicated that these young infants modulated the speed of their reaching movements to match task demands. Specifically, infants in the continuous group displayed increased peak speeds of their movements in order to contact a moving object. Results suggest that repeated opportunities to reach for objects underlies the emergence of reaching; however this process may be aided by providing a salient, multimodal link that highlights the effects of successful action.

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