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

Abstract

When a single light cue is given in the visual field, our eyes orient towards it with an average latency of 200 ms. If a second cue is presented at or around the time of the response to the first, a secondary eye movement occurs that represents a re-orientation to the new target. While studies have shown that eye movement latencies to 'single-step' targets may or may not be lengthened with age, secondary eye-movements (during 'double-step' displacements) are significantly delayed with increasing age. The aim of this study was to investigate if the postural challenge posed simply by standing (as opposed to sitting) results in significantly longer eye movement latencies in older adults compared to the young. Ten young (<35 years) and 10 older healthy adults (>65 years) participated in the study. They were required to fixate upon a central target and move their eyes in response to 2 types of stimuli: 1) a single-step perturbation of target position either 15º to the right or left, and 2) a double-step target displacement incorporating an initial target jump to the right or left by 15º, followed after 200 ms, by a shift of target position to the opposite side (e.g., +15º then -15º). All target displacement conditions were executed in sit and stand positions with the participant at the same distance from the targets. Eye movements were recorded using electro-oculography. Older adults did not show significantly longer eye movement latencies than the younger adults for single-step target displacements, and postural configuration (stand compared to sit) had no effect upon latencies for either group. We categorised double-step trials into those during which the second light changed after or before the onset of the eye shift to the first light. For the former category, young participants showed faster secondary eye shifts to the second light in the standing position, while the older adults did not. For the latter category of double-step trial, young participants showed no significant difference between sit and stand secondary eye movement latencies, but older adults were significantly longer standing compared to sitting. The older adults were significantly longer than the younger adults across both postural conditions, regardless of when the second light change occurred during the eye shift to the first light. We suggest that older adults require greater time and perhaps attentional processes to execute eye movements to unexpected changes of target position when faced with the need to maintain standing balance.

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

“…This aligns with previous discussion highlighting greater postural control during complex double-step saccades (Boulanger et al 2017). Also, an influence of posture on saccade initiation in younger adults was not evident for simple single-step saccades but accelerated the onset of a secondary saccade when standing under certain circumstances (Jimenez et al 2016). Further insights into the role of cognition on postural and visuomotor control could also be examined using the linear approach to threshold with ergodic rate (LATER) model (Noorani and Carpenter 2016).…”

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

“…A possible explanation for the differences in results between our study and the study by Dowiasch et al ( 2015 ) comes from the fact that participants in their study were actively locomoting through the environment, while our participants were passively transported along the route. It is conceivable that age-related differences in postural control (Jimenez et al, 2016 ), control of locomotion and steering cause differences in gaze behaviour. For example, Uiga et al ( 2015 ) suggest that older adults focus more on the lower portion of the visual field, potentially because they are more afraid of falling and therefore closely monitor the space just in front of them.…”