PhD Oral Exam - Laurence Lai, Psychology

When studying for a doctoral degree (PhD), candidates submit a thesis that provides a critical review of the current state of knowledge of the thesis subject as well as the student’s own contributions to the subject. The distinguishing criterion of doctoral graduate research is a significant and original contribution to knowledge.

Once accepted, the candidate presents the thesis orally. This oral exam is open to the public.

Abstract

It is known that executive functions (EFs) contribute increasingly to postural control as a function of age. However, there is a general lack of specificity in the work linking specific EFs to different balancing behaviours, and few cognitive mechanisms have been proposed to explain how individual EFs affect postural control in the context of aging. The aim of the current work is to examine the role that anticipation plays in postural control by applying the Dual Mechanisms of Control (DMC; Braver, 2012) framework to a postural recovery paradigm. The DMC framework posits that Proactive Control is the primary cognitive mechanism that drives age-related changes in anticipatory behaviours. Proactive Control has traditionally been examined through the AX-CPT, a computerized task that required participants to adjust their speeded motor responses depending on the cue and target combinations (Braver, 2012). In Study 1, 13 younger and 14 older adults underwent a novel postural recovery paradigm (Balance AX-CPT), a cued-postural recovery protocol which provided both valid and invalid cues that signalled potential platform movements. Anticipatory muscle activation (measured by electromyography) in a short time window following cue presentation served as the index of proactive control. Results suggested that overall, participants with stronger proactive control displayed significantly higher preparatory leg muscle activation to the valid cues regardless of age. In Study 2, the role of Proactive Control in postural recovery was further isolated in the context of aging by introducing a dual-task design. Seven younger and eleven older adults completed the Balance AX-CPT protocol that included a dual-task condition, in which participants performed a concurrent n-Back task should interfere with Proactive Control. Both age groups continued to display significantly higher preparatory muscle activation to valid cues, and there were also subtle indicators of postural prioritization that were primarily observed in older adult participants with weaker Proactive Control. Unexpectedly, both age groups showed dual-task facilitation on the concurrent cognitive task, which suggested that they engaged in attentional focus. Overall, the results provided experimental evidence for the anticipatory role that Proactive Control serves as the underlying mechanism for cued postural recovery in the context of aging.