Modifications with aging in the role played by vision and proprioception for movement control

Older adults rely on somatosensory information from the effector limb in the planning of discrete movements to somatosensory cues

While younger and older adults can perform upper-limb reaches to spatial targets with comparable endpoint accuracy (i.e., Helsen et al., 2016; Goodman et al., 2020), movement planning (i.e., reaction time) is significantly longer in older versus younger adults (e.g., Pohl et al., 1996; Goodman et al., 2020). Critically relevant to the current study, age-related differences in reaction time are even greater when older adults plan movement towards somatosensory versus visual or bimodal targets in the absence of vision of the moving limb (e.g., Goodman et al., 2020). One proposed explanation of these lengthened reaction times to somatosensory targets is that older adults may be experiencing challenges in implementing sensorimotor transformations when planning discrete movements of their unseen limb. To test this idea and assess the contributions of somatosensory information to these motor planning processes, tendon vibration was applied to the muscles of the effector limb between reaching movements made towards visual, somatosensory, or bimodal targets. The results revealed that older adults show the greatest increases in reaction times when vibration was applied during the preparation of movements to somatosensory targets. Further, both older and younger adults exhibited decreased movement endpoint precision when tendon vibration was applied. However, only older adults showed significantly lower movement endpoint precision due to tendon vibration when making movements to somatosensory targets, versus both visual and bimodal targets. These results corroborate previous evidence that older adults have difficulties planning upper-limb movements to somatosensory targets. As well, these results yielded novel evidence that such motor planning processes in older adult rely on somatosensory cues from the effector limb.

Investigation of Feedback Schedules on Speech Motor Learning in Older Adults

BACKGROUND

The principles of motor learning (PML) emerged from studies of limb motor skills in healthy, young adults. The applicability of these principles to speech motor learning, and to older adults, is uncertain.

AIMS

The purpose of this study was to examine one PML, feedback frequency, and its effect on retention and generalization of a novel speech and comparable tracing task.

METHODS

Sixty older adults completed a speech motor learning task requiring the production of a novel phrase at speaking rates 2 times and 3 times slower than habitual rate. Participants also completed a limb motor learning task requiring the tracing of a sine wave 2x and 3x slower than habitual rate. Participants were randomly assigned to receive feedback every trial, every 5th trial, or every 10th trial. Mean absolute error was measured to examine immediate generalization, delayed generalization, and 2-day retention.

FINDINGS

Results suggested that feedback frequency did not have an effect on the retention and generalization of the speech or manual task, supporting the small but growing literature highlighting the constraints of generalizing the PML to other modalities and populations.

Manual aiming in healthy aging: does proprioceptive acuity make the difference?

The present study examines whether non-active older adults are more dependent on visual information when executing aiming movements and whether age-related declines in proprioception play a mediating role herein. Young (N = 40) and older adults (N = 38) were divided into physically active and non-active subgroups based on self-reported sports participation levels. In experiment 1, participants executed wrist-aiming movements with and without visual feedback. In experiment 2, passive proprioceptive acuity was assessed using wrist motion detection and position matching tests. Results showed similar aiming accuracy across age groups both with and without visual feedback, but older adults exhibited longer movement times, prolonged homing-in phase, and made more corrective submovements. Passive proprioceptive acuity was significantly affected by physical activity level and age, with participants in the active group scoring better than their non-active peers. However, these declines did not predict performance changes on the aiming task. Taken together, our observations suggest that decline in proprioceptive acuity did not predict performance changes on the aiming task and older adults were able to compensate for their decreased motion and position sense when allowed sufficient time. In line with these observations, we proposed that older adults are able to compensate for their decline in proprioception by increasing their reliance on predictive models.

Impact of limiting visual input on gait: Individuals with Parkinson disease, age-matched controls, and healthy young participants

Normal and limited vision gait was investigated in individuals with Parkinson disease (PD), healthy older and healthy young individuals. Participants walked a GAITRite mat with normal vision or vision of lower limbs occluded. Results indicate individuals with PD walked more slowly, with shorter and wider steps, and spent more time in double support with limited vision as compared to full vision. Healthy young and old individuals took shorter steps but were otherwise unchanged between conditions.

Both age and physical activity level impact on eye-hand coordination

Aging impacts on our ability to perform goal-directed aiming movements. Older adults generally make slower and shorter initial impulses towards the end target, and therefore require more time for corrections in the final movement stage. Recent studies however suggest that a physically active lifestyle may attenuate these age-related changes. Also, it remains unclear whether eye-movement control exhibits a similar pattern of adaptation in older adults. Therefore, the first aim of this study was to describe how age and physical activity level impact eye-hand coordination during discrete manual aiming. Young and older participants were divided into physically active and sedentary subgroups, and performed discrete aiming movements while hand and eye movements were recorded. Secondly, to determine whether older adults depend more on vision during aiming, the task was repeated without visual feedback. The results revealed that the typical age-related hand movement adaptations were not only observed in older, but also in sedentary young participants. Older and sedentary young participants also spent more hand movement time after the eyes fixated the end target. This finding does not necessarily reflect an augmented reliance on vision, as all groups showed similar aiming errors when visual feedback was removed. In conclusion, both age and physical activity level clearly impacted eye-hand coordination during discrete manual aiming. This adapted coordination pattern seems to be caused by other factors than an increased reliance on vision.

Velocity discrimination: Reliability and construct validity in older adults

The aim of this study was to determine whether a test of velocity discrimination is a reliable and valid measure of proprioception in healthy older adults. Results revealed excellent test-retest reliability over a 2-week period. Velocity discrimination also indicated good construct validity with modest correlations with center of pressure sway outcomes in eyes open and closed conditions as well as stair climbing time. Good construct validity was identified by velocity discrimination sensitivity to age with a higher mean value for the older participants than for the younger participants. These findings suggest velocity discrimination is a valid and reliable measure of velocity sense, which may be included with measures of position and movement sense to enhance the proprioceptive testing repertoire among researchers. Implications of these results are discussed in terms of evaluation of proprioceptive training programs aimed to enhance postural control.

Age-related differences in the control of multijoint movements

The present study investigates whether regulation of interactive torque during multijoint movements decays with advanced age as a result of declines in the motor system. Young and elderly adults repeatedly drew a circle and ovals oriented in different directions using shoulder and elbow joint movements. Each template was traced at three levels of cycling frequency with and without vision. Although vision did not affect performance, increases in cycling frequency caused distortions of movement trajectories in both groups. The pattern of distortions differed, however, between the groups. These differences were accounted for by differences in elbow control. Young adults provided regulation of elbow amplitude and timing by matching muscle torque magnitude with increased interactive torque. In contrast, elderly adults did not increase muscle torque magnitude and modulated torque timing for elbow motion regulation. This strategy is discussed as adaptation to decrements in the aging motor system.

The effect of aging on adaptive eye-hand coordination

Perceptual-motor adaptability of older adults (65 and older) was assessed. Participants in two groups (younger, 20-36 years, and older, 67-87 years) pointed 100 times at a straight-ahead visual target while looking through laterally displacing prisms, with the hand visible early in the pointing movement. Aftereffect tests were administered after adaptation. Each group was then split into decay and readaptation subgroups in which respective treatments were given twice. After each treatment, aftereffect tests were readministered. Eye-hand total shift was significantly smaller for older participants, proprioceptive shift was not statistically smaller for older participants, and visual shift did not appear. Readaptation produced greater reduction in aftereffects than did decay; this effect was the same for both groups. The main conclusion is that perceptual-motor adaptability declines with advancing age.