Abstract
Purpose :
Numerous studies suggested that vision plays a crucial role in postural control. The purpose of the current presentation is to show that this visual-postural interplay is complex and may change either from one individual to another and, for one observer, according to task requirements.
Methods :
6 experiments were conducted. They followed the same global paradigm. Subjects stood, barefoot and arms along the body, in front of a projection screen. Optical motion sensors, located on a helmet, and 6 IR cameras (Optotrak system) were used to track and register head movements during each trial. The stimulus displayed on the screen was a black and white checkerboard with an empty grey area (5° of visual angle) in front of the subject’s eyes. The peripheral checkerboard could be either static or in motion: 2Hz periodic translation in Antero-Posterior (AP), Medio-Lateral (ML) directions. Within the 5° central area, fixation points, letters or words were displayed and used to change task requirements. Surrounding sound exposure was also controlled. Subjects were divided into 2 age groups (young adults vs 65yo and over), and 2 refractive error groups (myopes vs emmetropes).
Results :
Postural stability was assessed by calculating the Velocity Root Mean Square (VRMS) of head movements. Results showed that the amount of postural instability induced by peripheral motion changed according to viewing conditions, tasks and subjects groups. For instance, myopes’ balance control was more affected by the visual conditions than emmetropes. Subjects aged over 65 showed more vision dependency than young adults. Furthermore, the direction of motion, the cognitive load, the eye movement pattern, changed the postural response to visual stimuli. Our results did not provide evidence of a relation between visuo-postural response and the surrounding sound.
Conclusions :
Numerous studies showed that the role of vision in balance control increased with aging.
We confirmed this result and added that refractive error was also a factor of between-subject variation of vision-posture interplay. Our results also showed that the properties of the task (i.e. cognitive load; saccades vs fixation) and of sensory stimulation (AP and ML motion) were intra-individual factors of visually induced postural response variability. Furthermore, beyond the mean response to experimental conditions, we noticed a huge individual variability.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.