Elsevier

Gait & Posture

Volume 34, Issue 3, July 2011, Pages 340-346
Gait & Posture

Gaze strategies for avoiding obstacles: Differences between young and elderly subjects

https://doi.org/10.1016/j.gaitpost.2011.05.022Get rights and content

Abstract

Visual input is highly relevant for safely stepping over obstacles. In this study, gaze-behaviour was investigated in elderly, middle-aged and young subjects as they walked on a treadmill repeatedly stepping over obstacles, which approached either on the right or left side. In between obstacle-steps, subjects visually fixated a target N or F located two or four steps ahead on the floor, respectively. An acoustic warning signal announced the obstacles, after which subjects were free to look wherever they wanted. Gaze-movements were measured by video-oculography. Four conditions with 20 obstacles were conducted (two with target N, two with target F). In two conditions, high-precision stepping was investigated by asking subjects to step with minimal foot-clearance over the obstacles, while receiving acoustic feedback about their performance. In the high-precision conditions, more subjects (target N: 70%, F: 81%) turned their gaze on the obstacles and for a longer time than in unrestricted conditions. When fixating on the near target N and unrestricted stepping over the obstacles, significantly more elderly subjects (85%) turned their gaze on the obstacle compared to middle-aged (17%) and young subjects (29%). The elderly turned their gaze earlier and longer on the obstacle than middle-aged or young subjects. Our results reveal a different gaze-behaviour strategy of elderly subjects suggesting a greater dependency on visual inputs.

Introduction

Safe locomotion allows independent mobility in daily life, but requires a complex interaction of somatosensory, vestibular, and visual inputs. The latter seems to play a dominant role [1], [2]. Diminished afferent functions increase the risk of falling. Moreover, people who have experienced a fall may develop a fear of falling, jeopardizing their independence. The elderly in particular are prone to falling, with an incidence between 28% and 35% [3], [4], [5], [6], [7]. Falls are frequently caused by stumbling over obstacles [5], [7] such as uneven ground, curb stones or door steps [8], [9].

Several studies have shown different gait behaviours between young and elderly subjects during walking over challenging pathways. The elderly walked slower and with shorter steps over multi-surface terrain, such as slippery or uneven grounds [10]. Furthermore, they crossed an obstacle with a step more elongated than necessary for a safe landing position [11]. Their success rate for safe obstacle-avoidance was lower, the reaction time longer, the horizontal toe and heel distances to the obstacle were smaller, and the vertical foot-clearance was larger than in young subjects [12]. Elderly people adjusted their stepping pattern one step earlier than young subjects during walking over virtual obstacles [13].

Besides adjustments in gait parameters, gaze-behaviour appears also to be altered in aged people during challenging walking tasks. When instructed to step precisely on given targets, elderly subjects visually fixated these targets earlier and longer compared to young subjects [14]. During walking on a multi-surface terrain, elderly subjects needed more and prolonged visual inputs from the lower field than younger subjects [15]. In an obstacle-avoidance task with an additional cognitive challenge for selecting which limb crosses first over the obstacle, the elderly visually fixated the place where the leading foot should land for a longer time compared to young subjects [16]. Moreover, elderly fallers turned their gaze away from the obstacle earlier than elderly non-fallers in a dual-task condition [17].

The present study evaluates changes in gaze-behaviour during repetitive stepping over obstacles during normal and high-precision conditions in healthy young, middle-aged and elderly subjects. This investigation adds information to the existing literature, as several methodological approaches previously applied are now combined into one study. We evaluated changes in gaze-behaviour during repetitive obstacle steps (i) without restricting vision by using video-oculography, (ii) under equal conditions for each step to improve measurement accuracy, (iii) under some time pressure, and (iv) in three age groups. We hypothesized that (i) elderly subjects focus more on the obstacle and (ii) focussing on the obstacle is increased during high-precision conditions compared to unrestricted obstacle avoiding.

Section snippets

Participants

The experiment was approved by the Cantonal Ethic Commission Zurich. Participants gave informed and written agreement prior to data collection. Forty-four healthy subjects without orthopaedic or neurological disease participated and were classified in three groups: 17 subjects older than 60 years (average ±SD: 68.4 ± 5.5; range 63–81 years), all living independently and recruited at the Senior University Zurich; 12 middle-aged subjects (45.2 ± 5.5; range 35–53 years), recruited by advertisement via

Results

One-hundred and sixty out of 176 datasets (4 conditions × 44 subjects) could be analysed. The rest were of insufficient quality due to recording problems (e.g., no pupil detection because of closed eyelids). Results are presented in Table 1, Table 2.

Discussion

The present study investigated differences in gaze-behaviour between healthy elderly, middle-aged and young subjects during stepping over obstacles. We found that (i) compared to the younger subjects, more elderly turned their gaze on or into the direction of the obstacles in the near target condition, (ii) the elderly turned their gaze earlier and prolonged on or into the direction of the obstacles (except for condition F), (iii) in the high-precision conditions, more subjects turned their

Summary and conclusions

The results have highlighted different gaze-behaviour strategies during walking over obstacles in healthy well-performing elderly subjects, who did not report any falls. Our hypothesis was confirmed, as the elderly subjects looked earlier and prolonged at the obstacles than younger subjects. Additionally, in high-precision conditions, more elderly subjects used their visual input and turned the gaze downward to the obstacles compared to the younger ones, who might have better used peripheral

Conflict of interest

We report no conflict of interests. The financial and personal supports of this study are mentioned in the acknowledgement and had no influence at all on the presentation of the results of this study.

Acknowledgments

We thank Johannes Vockeroth, Stefan Kohlbecher and Andreas Häussler of the EyeSeeCam-team for technical support. We also thank the volunteers for their willingness to take part in our investigations. This work was financial supported by the Zurich Center for Integrative Human Physiology, the Betty and David Koetser Foundation for Brain Research, and the Swiss National Science Foundation.

References (28)

  • J. Stevens et al.

    Dogs and cats as environmental fall hazards

    J Saf Res

    (2010)
  • P. Kennedy et al.

    Relative contributions of visual and vestibular information on the trajectory of human gait

    Exp Brain Res

    (2003)
  • A. Blake et al.

    Falls by elderly people at home: prevalence and associated factors

    Age Ageing

    (1988)
  • S. Buatois et al.

    Posturography and risk of recurrent falls in healthy non-institutionalized persons aged over 65

    Gerontology

    (2006)
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