Visuospatial working memory and obstacle crossing in young and older people

Abstract

Obstacle crossing requires visuospatial working memory to guide the trailing leg trajectory when vision in unavailable. Visuospatial working memory, as assessed with neuropsychological tests, declines with age, however, this remains to be investigated functionally in obstacle crossing. There is also evidence that visuospatial encoding during a secondary task interferes with balance control during stepping and walking in older people. Here, we studied the interaction effects of age by delay (study 1) and age by secondary visuospatial task (study 2) conditions on obstacle clearance in a visuospatial working memory -guided obstacle crossing task. Healthy young adults aged 19 to 36 years (n = 20 in study 1 and n = 17 in study 2) and healthy older adults aged 66 to 83 years (n = 29 in study 1 and n = 21 in study 2) were instructed to step over an obstacle with their leading leg and straddle it for a delay period before completing the crossing with their trailing leg. In study 1, two obstacle height conditions (12 cm, 18 cm) and two delay durations (20 s, 60 s) were presented in random order. In study 2, participants were required to attend to either no secondary task (control), a visuospatial secondary (star movement) task, or a nonspatial secondary (arithmetic) task, while straddling the obstacle for a delay duration of 20 s, at obstacle heights of 12 cm and 18 cm, randomly presented. Trailing leg kinematics (mean and variability of maximum toe clearance over the obstacle) were determined via motion capture. There were no statistically significant age by delay or age by secondary task interactions. In study 1, toe clearance variability was significantly greater in young adults and increased with increasing delay duration in both groups. In study 2, compared with the control condition, toe clearance variability was significantly greater in the non-spatial secondary task condition but not in the visuospatial condition. Contrary to our hypotheses, these findings suggest that young and older adults alike can store an obstacle representation via visuospatial working memory for durations of at least 60 s and use this information to safely scale their trailing leg over an obstacle. However, the increase in trailing leg toe clearance variability with delay duration suggests that obstacle representation starts to deteriorate even within the first 20 s regardless of age. The finding that undertaking a concurrent arithmetic task impaired visuospatial working memory-guided obstacle clearance suggests a potential increased risk of tripping during obstacle crossing while dual-tasking in both young and older people.

Keywords: Aged; Obstacle avoidance; Secondary task; Visuospatial processing; Working memory.

Fig. 1

a The obstacle (denoted by the green rod) attached at one end to a holder. b frontal view of the obstacle (denoted by the green bar) set at each of the two obstacle heights

Fig. 2

Sequence of steps in the obstacle-straddling paradigm; a overhead view of the sequence of foot placements taken by participants to step over the obstacle (green bar denotes the obstacle; footprints denote sequence of foot placements). b lateral view of the steps taken by participants to step over the obstacle; first crossing it with the leading leg, then pausing and straddling the obstacle for a delay duration during which the obstacle was lowered to the ground, before subsequently stepping over the obstacle with the trailing leg (green dot denotes the obstacle; arrow denotes the obstacle being lowered to the ground; dotted circle denotes original height of the obstacle before being lowered)

Fig. 3

Study 1 a mean TC showed no age by delay interaction effect. b TC variability showed no age by delay interaction effect. c mean TC showed an age by height interaction effect. Low 12 cm obstacle height. High 18 cm obstacle height. Lines and error bars represent means and standard deviations

Fig. 4

Study 2 a mean TC showed no age by condition interaction effect. b TC variability showed no age by condition interaction effect. Lines and error bars represent means and standard deviations. NS nonspatial. VS visuospatial