Biology subjects

Georgiadis, P.

Publications and source records attributed to Georgiadis, P..

3 recordsLinked to original sources

bioRxiv2025

Head engagement during visuomotor tracking is determined by postural demands and aging

Vision is important for various tasks, from visually tracking moving objects to maintaining balance. People obtain visual information through eye movements performed either alone or in combination with head movements. Even when isolated eye movements can accommodate the amplitude of the desired gaze shift, humans still perform head movements, as they provide additional sensory signals that can be integrated with retinal input resulting in improved gaze estimates. However, head movements also create mechanical torques and attenuate vestibular processing that could disturb balance. We, therefore, here examined whether head engagement is determined by postural requirements when performing a visual tracking task. Young participants visually tracked a target moving horizontally along different amplitudes, while they were seated, standing on a firm and an unstable surface. Our results showed stronger head engagement when standing than sitting, but no systematic differences were found between firm and unstable surfaces. To further explore the interplay between head engagement and postural demands, we conducted a second experiment where young and older participants performed a similar task, but now they were either allowed to move their head or instructed to limit their head movements. Both tracking accuracy and postural sway increased when engaging the head. When asked to limit head movements, both age groups engaged their head minimally, but head movements were more pronounced in more challenging postures. When allowed to move their head naturally, younger participants engaged their head more when standing than sitting, but older adults reduced their head movements with more demanding postures. We suggest that head movements in younger adults facilitate visual tracking, while limited head movements in older adults preserve balance.

neuroscience↗

bioRxiv2024

Reliability of tactile perception and suppression measurements

Tactile signals arising on ones own body allow estimation of ones own sensory state and foster interactions with the environment. However, tactile perception can be influenced by various factors. For instance, tactile perception is suppressed on a moving limb compared to when it is resting, a phenomenon termed tactile suppression. Here we examine whether tactile perception during resting and during movement is robust over shorter and longer time intervals. Participants had to detect tactile stimuli of various intensities on their index finger while this finger was resting or moving (finger extension). This detection task was performed on four sessions at separate days across a period of one month. We found that tactile perception during resting is robust within single sessions and across days. However, tactile perception during movement changed across days, but these changes lacked a clear systematic pattern. We further show that temporal changes in perception alone cannot fully account for the previously reported tactile suppression effects. Finally, split-half correlations reveal high consistency in the estimated perceptual measures, demonstrating that estimates of tactile perception are robust across measurement points.

physiology↗

bioRxiv2022

Standing balance in aging is robust against head rotation during visual tracking.

Standing balance is relatively more unstable when visually pursuing a moving target than when fixating a stationary one. These effects are common across age groups if the head is restrained during visual task performance. The present study focused on the role of the head motion on standing balance during the pursuit of a moving target as a function of age. Three predictions were tested: a) standing balance is compromised to a greater extent in older than young adults by gaze target pursuit compared to fixation, b) older adults pursue a moving target with greater and more variable head rotation than young adults, and c) greater and more variable head rotation during the gaze pursuit task is associated with greater postural sway. Twenty-two (22) older (age: 71.7{+/-}8.1, 12 M / 10 F) and twenty-three (23) young adults (age: 23.6{+/-}2.5, 12 M / 11 F) stood on a force plate in front of a 60-inch monitor while performing two visual tasks: fixation at a stationary target and gaze pursuit of a horizontally moving target. Centre of pressure (CoP) and head kinematics were synchronously recorded with the Vicon motion analysis system, while head-unconstrained gaze was captured by the Pupil Labs Invisible mobile tracking system. Postural sway, reflected in the interquartile CoP range and the root mean square (RMS) of CoP velocity increased during the gaze pursuit compared to the fixation task (p<.05), and this effect was more pronounced in older than young participants (p<.05). Older adults pursued the moving target employing more variable (p=.022) head yaw rotation than young participants although the amplitude of head rotation was not systematically different between groups (p=. 077). The amplitude and variance of head yaw rotation did not correlate with postural sway measures. Results suggest that older adults may engage more variable head rotation when tracking a moving target to compensate for age-related deficits in eye smooth pursuit movement. However, this strategy does not seem to compromise standing balance.

neuroscience↗