The online control of visually guided movement across the lifespan

Abstract

The online control of movement is essential to the flexible control of eye-hand coordinated action. As people age, there is evidence to suggest that various aspects of both motor and visual performance decline. While some aspects of eye-hand coordination have been extensively studied in an ageing population, the online control of goal directed movement has received less attention. The aim of this thesis is to understand how healthy ageing impacts the online control of visually guided movement. The manuscripts in this thesis used a target perturbation paradigm and manipulated the time at which a target perturbation occurred to investigate how healthy ageing impacts visually guided motor control. Early, mid and later times during the reach were selected to determine how each group was able to use the available time to correct their reach. Eye movement, hand movement or a combination of such was recorded and performance was considered across age groups and target perturbation times. Overall, the results demonstrate that while both younger and older participants were able to compensate for target perturbations that occurred earlier in the movement, the difficulties in compensating for target perturbations that occurred later in the reach were exacerbated in older participants. Manuscript 1 demonstrated that older participants had significantly increased movement times and longer saccade latencies compared to younger participants. Manuscript 2 showed that older participants were slower overall and produced a correction to a change in target location proportionally less often than younger participant, with effects exacerbated in the later perturbation time condition. Manuscript 3 furthered the results of Manuscripts 1 and 2 and demonstrated that that older participants were both slower to initiate a correction in response to a target perturbation and did so less frequently. Older participants also had slower saccade latencies to targets pre and post target perturbation with a correlation across both groups between the eye and the hand position at the time of movement completion. These results suggest that the age-related effects on performance may be due in part to a delay in the acquisition of visual information to inform the reaching movement, stemming from the increase in saccade latencies pre and post target perturbation for older participants. Taken together, the results of this thesis demonstrate that hand-eye coordination during online control is impacted by healthy ageing.