Posture and gaze tracking of a vertically moving target reveals age-related constraints in visuo-motor coupling

Abstract

Previously we have demonstrated that the effect of aging on posture and gaze active tracking of a visual target moving in the horizontal direction is dependent on target’s complexity. In this study, we asked whether a similar phenomenon is present when tracking a visual target moving with varying complexity in the vertical direction. Ten young (22.98 ± 2.9 years) and 10 older adults (72.45 ± 4.72 years) tracked for 120 s, a visual target moving vertically by shifting their bodyweight in the anterior-posterior direction. Three target motions were tested: a simple periodic (sine wave), a more complex (Lorenz attractor) and an ultra-complex random (Surrogated Lorenz attractor) pattern. Cross-spectral analysis revealed lower sway-target coherence as a function of age, regardless of target motion’s complexity. This age effect was significant for the sway-target gain but not for the phase index. Gaze-target analysis revealed age related differences only when tracking the more complex targets. Regardless of age, tracking of the complex target was associated with lower cross Approximate Entropy. It is concluded that tracking of visual targets oscillating in the vertical direction reveals age related constraints that are independent of visual motion’s complexity. These constraints are evident in the spatial and not temporal aspects of visuo-motor coupling, which suggests the presence of neuromuscular deficiencies in controlling visually guided postural sway in the anterior-posterior direction.

Center of Pressure Feedback Modulates the Entrainment of Voluntary Sway to the Motion of a Visual Target

“…Tracking of the chaotic target resulted in lower coherence, greater target overshooting, and a longer phase lag between the target and the CoP motion when compared to periodic target tracking. These results confirm previous findings from our laboratory showing that voluntary, sagittal plane sway synchronizes better with predictable (i.e., periodic) target motion than less predictable (i.e., chaotic) target motion when actively tracking a vertically moving target [12,16]. It could be suggested that postural tracking of the chaotic target imposed more extensive visuo-motor processing due to the less predictable nature of the target's motion, which may have kept participants more actively engaged in the tracking task due to the continuous need to attend to the target motion.…”

“…The predictable signal was a sinewave with a single frequency (f) set at 0.25 Hz that was generated using the sin function [sine = sin(2pi × f × t)]. This particular frequency was selected because it was the dominant frequency of intuitive, self-paced voluntary sway based on prior studies [12,16] and pilot testing. The less predictable signal was derived from a Lorenz attractor according to the parameters: σ = 10, β = 8/3, and r = 28 and the initial conditions: x0 = 0.1, y0 = 0.1, and z0 = 0.1.…”

“…The role of visual feedback when actively tracking a moving visual target with the whole body is less studied. Work from our laboratory suggests that humans, regardless of their age, can couple their voluntary sway to a moving visual target regardless of whether this oscillates in a stereotypical (i.e., periodically) or in a more complex (i.e., chaotically) fashion [12]. However, the role of CoP feedback in visuo-postural entrainment and its dependence on target predictability is still not known.…”

“Walking” through the sensory, cognitive, and temporal degradations of healthy aging

“…The latter deficits can be targeted by multisensory processing strategies that can facilitate performance since they require the additional recruitment of parietal and prefrontal areas, which compensates for the sensory impairments in bottom‐up processing during executive control (i.e., Hemispheric Asymmetry Reduction in OLDer adults—HAROLD model) . Multisensory stimulation could, therefore, enhance cognitive processing, assist the elderly to rely on more than one modality during gait and postural control, and possibly yield transfer effects in critical everyday tasks, including visuomotor coordination, balance maintenance and gait control, estimation of body motion in space, detection of changes in head acceleration, perception of peripersonal space, and reduction of cognitive‐motor interference in dual tasking when the secondary task includes a visualization component …”

Standing on unstable surface challenges postural control of tracking tasks and modulates neuromuscular adjustments specific to task complexity

“…The periodic signal was a sinewave with a single frequency (f) set at 0.25 Hz that was generated using the sin function . The particular frequency was selected because this is the dominant frequency of natural, self-paced voluntary sway 30 , 31 . The chaotic signal was derived from a Lorenz attractor, according to the parameters: σ = 10, β = 8/3 and r = 28 and the initial conditions: x 0 = 0.1, y 0 = 0.1 and z 0 = 0.1.…”