Age-related effects of increasing postural challenge on eye movement onset latencies to visual targets

[Effects of postural control upon anti-saccade error rate in older people]

BACKGROUND

The anti-saccadic (AS) error-rate is used to diagnose neurological disorders. The natural aging process could generate difficulty in carrying out parallel neural processes of conscious motor inhibition and eye movement. Therefore, if balance control is imposed on an elderly person in biped positions during an AS movement, an increase in the AS error-rate is expected.

OBJECTIVE

To study the effects of postural control on the AS error-rate in older people.

METHODS

An intra and intergroup comparison was made of AS error-rate in an experimental group of older people (PM) and another control group of young people (PJ). For this, blocks of AS and pro-saccadic movements (control) were used randomly in four different postures: (1)sitting (SENT), (2)standing normally (NORMAL), (3)feet together (REDUC), and (4)feet in line (TANDEM).

RESULTS

The PM group, compared to the PJ group, showed a progressive increase in the AS error-rate from the sitting position to all standing positions, with the maximum AS error-rate in more complex vertical postures. In contrast, the PJ group did not present significative variability of this AS error-rate in all positions.

CONCLUSIONS

It is confirmed that the aging process is associated with an increase in the AS error-rate. This study reveals for the first time a significant increase in the AS error-rate when control of body balance is required for PM, implying a decrease in the multiple processing capacity in PM for the execution of complex and parallel tasks.

Are age-related deficits in route learning related to control of visual attention?

Typically aged adults show reduced ability to learn a route compared to younger adults. In this experiment, we investigate the role of visual attention through eye-tracking and engagement of attentional resources in age-related route learning deficits. Participants were shown a route through a realistic virtual environment before being tested on their route knowledge. Younger and older adults were compared on their gaze behaviour during route learning and on their reaction time to a secondary probe task as a measure of attentional engagement. Behavioural results show a performance deficit in route knowledge for older adults compared to younger adults, which is consistent with previous research. We replicated previous findings showing that reaction times to the secondary probe task were longer at decision points than non-decision points, indicating stronger attentional engagement at navigationally relevant locations. However, we found no differences in attentional engagement and no differences for a range of gaze measures between age groups. We conclude that age-related changes in route learning ability are not reflected in changes in control of visual attention or regulation of attentional engagement.

Do postural constraints affect eye, head, and arm coordination?

If a whole body reaching task is produced when standing or adopting challenging postures, it is unclear whether changes in attentional demands or the sensorimotor integration necessary for balance control influence the interaction between visuomotor and postural components of the movement. Is gaze control prioritized by the central nervous system (CNS) to produce coordinated eye movements with the head and whole body regardless of movement context? Considering the coupled nature of visuomotor and whole body postural control during action, this study aimed to understand how changing equilibrium constraints (in the form of different postural configurations) influenced the initiation of eye, head, and arm movements. We quantified the eye-head metrics and segmental kinematics as participants executed either isolated gaze shifts or whole body reaching movements to visual targets. In total, four postural configurations were compared: seated, natural stance, with the feet together (narrow stance), or while balancing on a wooden beam. Contrary to our initial predictions, the lack of distinct changes in eye-head metrics; timing of eye, head, and arm movement initiation; and gaze accuracy, in spite of kinematic differences, suggests that the CNS integrates postural constraints into the control necessary to initiate gaze shifts. This may be achieved by adopting a whole body gaze strategy that allows for the successful completion of both gaze and reaching goals.

NEW & NOTEWORTHY Differences in sequence of movement among the eye, head, and arm have been shown across various paradigms during reaching. Here we show that distinct changes in eye characteristics and movement sequence, coupled with stereotyped profiles of head and gaze movement, are not observed when adopting postures requiring changes to balance constraints. This suggests that a whole body gaze strategy is prioritized by the central nervous system with postural control subservient to gaze stability requirements.