The influence of gaze stabilization and fixation on stepping reactions in younger and older adults.

Purpose: To date, there has been little evidence to suggest the importance of foveal viewing versus peripheral retina viewing when trying to recover from a perturbation. The purposes of this investigation were to (1) determine whether a visual target can be stabilized on the fovea during a perturbation, (2) determine whether stepping responses following a perturbation are influenced by foveal fixation, and (3) compare gaze stability and stepping responses between young and aging adults.

Materials/methods: Ten young adults and 10 aging adults were asked to wear an eye-tracking device linked to a kinematic tracking system during perturbations. Perturbations were delivered under 2 conditions: control (no instructions regarding gaze location were given) and earth-fixed (EF) (subjects were asked to fixate gaze on an EF target). Stepping responses were recorded via force plates. Gaze stability, reported as percent foveal fixation (% FF), was calculated from eye-tracking data. Step latencies (SLs) were computed from force plate data. A 2 x 2 analysis of variance was used to assess statistical significance between groups. For the young and aging adults, linear correlations were made to identify relationships between % FF and SL.

Results: For each condition, aging adults took longer to initiate a step (control, P = .002; EF, P = .003). Young adults were better at maintaining gaze fixation than older adults (P = .0045). Linear correlations demonstrated significant negative relationships between SL and % FF for young (r = -0.76, P = .001) and older (r = -0.87, P = .0001) adults. As % FF increased, SL decreased.

Conclusions: The ability to maintain gaze fixation of an EF target may be important in reducing SL following a perturbation. Older adult subjects demonstrated a decreased ability to fixate a target during balance tasks while also displaying longer SLs.