Improvements in Obstacle Clearance Parameters and Reaction Time Over a Series of Obstacles Revealed After Five Repeated Testing Sessions in Older Adults

The effect of visual sensory interference during multitask obstacle crossing in younger and older adults

When older adults step over obstacles during multitasking, their performance is impaired; the impairment results from central and/or sensory interference. The purpose was to determine if sensory interference alters performance under low levels of cognitive, temporal, and gait demand, and if the change in performance is different for younger versus older adults. Participants included 17 younger adults (20.9±1.9 years) and 14 older adults (69.7±5.4 years). The concurrent task was a single, simple reaction time (RT) task: depress button in response to light cue. The gait task was stepping over an obstacle (8 m walkway) in three conditions: (1) no sensory interference (no RT task), (2) low sensory interference (light cue on obstacle, allowed concurrent foveation of cue and obstacle), or (3) high sensory interference (light cue away from obstacle, prevented concurrent foveation of cue and obstacle). When standing, the light cue location was not relevant (no sensory interference). An interaction (sensory interference by task, p<0.01) indicated that RT was longer for high sensory interference during walking, but RT was not altered for standing, confirming that sensory interference increased RT during obstacle approach. An interaction (sensory interference by age, p<0.01) was observed for foot placement before the obstacle: With high sensory interference, younger adults placed the trail foot closer to the obstacle while older adults placed it farther back from the obstacle. The change increases the likelihood of tripping with the trail foot for younger adults, but with the lead limb for older adults. Recovery from a lead limb trip is more difficult due to shorter time for corrective actions. Overall, visual sensory interference impaired both RT and gait behavior with low levels of multitask demand. Changes in foot placement increased trip risk for both ages, but for different limbs, reducing the likelihood of balance recovery in older adults.

The influence of carrying an anterior load on attention demand and obstacle clearance before, during, and after obstacle crossing

Carrying an anterior load during obstacle negotiation increases attention demand, which may differ at various crossing stages. Less is known on the impact of lower visual field obstruction and the weight of the anterior load on obstacle negotiation and attention demand. The objectives of this study were to: (1) determine if carrying a weighted anterior load, lower visual field occlusion, or both, modify obstacle clearance and/or reaction time (RT); and (2) examine whether RT is modulated across obstacle crossing phases as measured by a probe RT protocol. Sixteen young adults crossed an obstacle while carrying no load, a clear 5 kg load, and an opaque 5 kg load, while performing a simple RT task. Auditory stimuli were presented at five locations: (1) two steps before the obstacle; (2) one step before the obstacle; (3) as the leading limb crossed the obstacle; (4) as the lead limb touched down after the obstacle; and (5) as the trail limb crossed the obstacle. The toe clearance height of the leading limb was greatest for the weighted opaque box load type followed by the weighted clear box type compared to the no box load type. Carrying an anterior load during obstacle crossing did not influence RT. RTs were longer at the pre-crossing and beginning of the crossing phases compared to after-crossing phases. Results suggest that carrying a weighted anterior load and lower visual field occlusion increase the risk for tripping. Attention demands differ across obstacle crossing phases during dual-tasking and should be considered in fall-risk assessments.

Medication and trial duration influence postural and pointing parameters during a standing repetitive pointing task in individuals with Parkinson's disease

We aimed to determine the effects of levodopa medication on the performance of a repetitive pointing task while standing, and to investigate the optimal trial duration in individuals with Parkinson’s disease, and older adults. Seventeen individuals with Parkinson’s disease (5 freezers) and 9 older adults stood on force platforms for 30 s and 120 s while performing a bilateral repetitive pointing task, tracked by motion capture. Participants with Parkinson’s disease were assessed on and off medication and older adults were also assessed on separate days. The main findings were that: 1) on medication, participants with Parkinson’s exhibited greater center of pressure root mean square in the medial-lateral direction, greater velocity in the medial-lateral and anterior-posterior directions, and greater range in the medial-lateral direction than off medication; 2) longer trial durations resulted in greater center of pressure range in the medial-lateral and anterior-posterior directions and greater coefficient of variation in finger pointing on the least affected side; 3) Parkinson’s participants exhibited larger range in the medial-lateral direction compared to older adults; 4) off medication, freezers presented with less range and root mean square in the anterior-posterior direction than non-freezers; and 5) a correlation emerged between the freezing of gait questionnaire and pointing asymmetry and the coefficient of variation of pointing on the most affected side. Therefore, Parkinson’s medication may increase instability during a repetitive pointing task. Longer trials may provide a better depiction of sway by discriminating between those with and without neurological impairment. Individuals with Parkinson’s were less stable than older adults, supporting that they are at a greater risk for falls. The greater restrictive postural strategy in freezers compared to non-freezers is likely a factor that augments fall-risk. Lastly, the link between freezing of gait and upper-limb movement indicates that freezing may manifest first in the lower-limbs.