Biology subjects

Voudouris, D.

Publications and source records attributed to Voudouris, D..

15 recordsLinked to original sources

bioRxiv2026

Tactile suppression during movement as optimal integration of somatosensory feedback across time

Goal-directed movements generate tactile signals from the moving body, yet many are perceptually suppressed. Prevailing accounts propose that the nervous system reduces tactile sensitivity by prioritizing internal predictions over somatosensory feedback, contrasting with the view that suppression reflects peripheral masking. However, both accounts lack quantitative explanations of temporal dynamics and dependence on the motor task. Here, we show that tactile suppression is a consequence of optimal state estimation during movement. Using optimal feedback control theory, we derived how the nervous system should dynamically weight uncertain internal predictions against noisy somatosensory feedback. Human participants performed goal-directed reaching movements while vibrotactile stimuli were delivered at different time points. Suppression weakened as internal uncertainty about hand distance to target increased, consistent with greater reliance on sensory feedback. Model comparison identifies tactile suppression as dynamic, uncertainty-dependent state estimation rather than peripheral masking, establishing a normative principle for tactile sensitivity during action.

neuroscience↗

bioRxiv2026

Temporal dynamics of early somatosensory processing in goal-directed actions

Tactile sensitivity is temporally modulated on a moving limb. Yet the neural mechanisms underlying this modulation remain unclear. Using electroencephalography, we examined the temporal dynamics of early somatosensory processing during goal-directed reaching. Participants reached for their unseen left hand while brief vibrations were applied to the moving right index finger in different movement phases. Psychophysical results revealed overall tactile suppression during reaching, with sensitivity transiently improving around maximum speed relative to the late movement phase. Consistent with the psychophysical data, the short-latency P45 component, originating in primary somatosensory cortex, was suppressed during reaching but recovered around maximum speed. Reduced P45 amplitudes were associated with stronger tactile suppression measured behaviorally, linking early cortical activity to perceptual changes. This temporally specific modulation of tactile perception, associated with early cortical processing, suggests that the somatosensory system dynamically adapts its sensitivity to facilitate sensorimotor control in goal-directed actions. Significance statementThe perception of touch on a moving hand varies across different movement phases, depending on the importance of sensory feedback for guiding the hand. Our results show that these changes in perception are linked to modulations in early brain activity, indicating that the central nervous system adjusts touch processing in a time-sensitive manner at early processing stages to facilitate control of goal-directed actions.

neuroscience↗

bioRxiv2025

Adaptive Eye Movement Behavior for Actions in Younger and Older Adults

Humans typically combine eye and head movements to visually track and interact with moving objects. If the objects trajectory can be predicted, humans can shift gaze to the anticipated objects future location. For instance, when hitting a moving ball, people predictively look at the balls bouncing location, allowing them to overcome sensorimotor delays that would otherwise limit visual information uptake from that position. Such delays become pronounced with healthy aging, which might drive a behavioral shift towards stronger reliance on predictive gaze allocation to future positions of interest during visuomotor tasks. To investigate this, we examined gaze and hand movements of older and younger adults who played an iPad-based version of the game Pong against an automated opponent. Participants moved a paddle of two different sizes with their finger to intercept a ball moving in two speeds and bouncing off the side walls. We hypothesized that aging would lead to earlier gaze shifts to positions of interest, such as to the final wall bounce location before the ball moved toward the participants paddle, and to their own paddle around the moment of interception. As expected, both age groups intercepted fewer balls when using smaller paddles. Contrary to our hypothesis, older participants looked later than younger adults to the final wall bounce. However, they shifted their gaze earlier to their own paddle before interception, especially at the beginning of the experiment. This suggests that aging enhances predictive gaze shifts related to the immediate action. While gaze allocation patterns largely overlap between older and younger adults, aging specifically leads to adaptive eye movements just before interacting with the environment.

neuroscience↗

bioRxiv2025

Modulation of tactile sensitivity in the lower limbs during goal-directed movements

Tactile sensitivity drops in a moving than static limb due to a combination of central, predictive mechanisms and peripheral effects. This suppression is dynamically modulated during movement, as shown during upper-limb actions, yet little is known about its implication during complex lower-limb movements. We investigated tactile sensitivity during naturalistic kicking by delivering vibrotactile probe stimuli to the balancing and kicking feet at different movement phases. In Experiment 1, participants kicked a suspended ball while tactile sensitivity was probed at movement onset, mid-swing, ball contact, and after-contact. Results revealed distinct modulation patterns in each foot. When transitioning from bipedal to unipedal stance, tactile processing at the balancing foot was particularly suppressed but at the kicking foot it improved, suggesting concurrent modulation across the two legs depending on their motor function. Tactile sensitivity remained rather invariant at other time points, but was strongly suppressed on the kicking foot at the moment of ball contact. The strength of this suppression correlated with kicking speed, which could reflect either stronger predictive control or stronger peripheral processes that mask the vibrotactile probe. To test these, a new set of participants held their foot still while a ball collided with it at high or low speed. Suppression was greater with faster ball contacts, revealing that peripheral processes can modulate tactile processing. These findings show that lower-limb tactile sensitivity during goal-directed leg movements can be concurrently modulated across the legs, presumably reflecting an interplay between central sensorimotor processes guiding the movement and peripheral processes affecting sensitivity. Significance StatementTactile sensitivity is known to fluctuate during movement, but little is understood about how it is tuned during complex lower-limb actions. Using a naturalistic ball-kicking task, we reveal distinct modulation patterns in the balancing and kicking feet, showing that postural and guiding demands dynamically shape tactile sensitivity. We further demonstrate that the strength of tactile modulation is influenced by peripheral processes, such as tactile masking. These findings highlight that lower-limb tactile processing can be flexibly and concurrently modulated in the two legs during state transitions that impose different sensorimotor demands for complex natural behavior.

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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

Gaze when walking to grasp an object in the presence of obstacles

People generally look at positions that are important for their current actions, such as objects they intend to grasp. What if there are obstacles on their path to such objects? We asked participants to walk into a room and pour the contents of a cup placed on a table into another cup elsewhere on the table. There were two small obstacles on the floor between the door and the table. There was a third obstacle on the table near the target cup. Participants mainly looked at the items on the table, but as they approached and entered the room they often looked at the floor near the obstacles, although there was nothing particularly informative to see there. They relied on peripheral vision and memory of where they had seen obstacles to avoid kicking the obstacles. From well before participants crossed the obstacles, they primarily looked at the object that they intended to grasp. We conclude that people look at positions at which they plan to interact with the environment in a specific manner, rather than at items that constrain such interactions.

neuroscience↗

bioRxiv2024

Postural demands modulate tactile perception in the lower limb in young and older adults

Balance control requires constant integration of feedforward and feedback signals. In healthy aging, the quality of feedback signals decreases while feedforward control is upweighted; but it is unclear how tactile perception is modulated when balance control is challenged and how this interacts with age-related changes in sensorimotor processes. We therefore examined tactile perception in standing when confronted with different postural demands in young and older adults. To this end, we measured tactile sensitivity on the calf during sitting (baseline), standing on solid ground, and standing on unstable ground (foam). We also measured the center of pressure during standing using a force plate and calculated a 95% confidence ellipse area and the center of pressure length. Tactile sensitivity was assessed by fitting a psychometric function to verbal responses for detecting vibrotactile probes, calculating the detection threshold at 50% detection, and normalizing the two standing conditions to baseline. We examined the effect of age and postural demands on the center of pressure kinematics and detection thresholds. We found higher sway and poorer tactile sensitivity when standing on foam irrespective of age. The increase of postural demands seems to reduce the reliance on tactile feedback signals from the lower limbs in both young and older adults. Our results suggest that postural demands challenge healthy agers as young adults, probably leading to a down-weighting of tactile feedback processing.

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↗

bioRxiv2023

Visual perturbations temporally tune balance retention and associated tactile processing

Somatosensory feedback is essential for motor control, yet sensations from ones own movements are often suppressed. Despite extensive research on movement-induced tactile suppression, its mechanisms remain unclear. Most studies focus on simple upper-limb movements, leaving the generalization to other body parts unexplored. This study examines tactile processing on the lower limb during balance control by varying feedback processing demands. Participants experienced visual perturbations in a virtual room challenging their posture. Tactile sensitivity was assessed using vibrotactile stimuli to the lower leg at different times around the perturbation. We found that postural behavior is both predictively tuned before and reactively adjusted to expected perturbations. Our results provide evidence that tactile sensitivity changes according to feedback processing demands on the lower limb. Such dynamic sensory modulation could reflect the continuous up- and down-regulation of feedback signals to accomplish the task at hand.

neuroscience↗

bioRxiv2023

Sensorimotor memories influence movement kinematics but not associated tactile processing

When interacting with objects, we often rely on visual information. However, vision is not always the most reliable sense for determining relevant object properties. For example, when the mass distribution of an object cannot be inferred visually, humans may rely on predictions about the objects dynamics. Such predictions may not only influence motor behavior but also associated somatosensory processing, as sensorimotor predictions lead to reduced tactile sensitivity during movement. We examined whether predictions based on sensorimotor memories influence grasping kinematics and associated tactile processing. Participants lifted an object of unknown mass distribution and reported whether they detected a tactile stimulus on their grasping hand during the lift. In Experiment 1, the mass distribution could change from trial to trial, whereas in Experiment 2, we intermingled longer with shorter parts of constant and variable mass distributions, while also providing implicit or explicit information about the trial structure. In both experiments, participants grasped the object by predictively choosing contact points that would compensate the mass distribution experienced in the previous trial. Tactile suppression during movement, however, was invariant across conditions. These results suggest that predictions based on sensorimotor memories can influence movement kinematics but may not affect associated tactile perception. Public significance statementTo perform a goal-directed movement, such as grasping an object, humans combine the available sensory information with predictions about the prevailing dynamics. Sensorimotor predictions also lead to a decrease of movement-related tactile signals, a phenomenon termed tactile suppression. Tactile suppression is supposed to rely on a dynamic weighting of sensory feedback and predictive signals. When sensory feedback is not reliable, reliance on memory-based predictions may be desired. Here we show that motor behavior is influenced by predictions based on sensorimotor memories, but associated tactile processing appears to be robust.

neuroscience↗

bioRxiv2023

Pupil dilation scales with movement distance of real but not of imagined reaching movements

Pupillary responses have now been reliably identified for cognitive and motor tasks, but less is known about their relation to mentally simulating movements (known as motor imagery). Previous work found pupil dilations during the performance of simple finger movements, where peak pupillary dilation scaled with the complexity of the finger movement and force required. Recently, pupillary dilations were reported during imagery of grasping and piano playing. Here we examined whether pupillary responses are sensitive to the dynamics of the underlying motor task for both executed and imagined reach movements. Participants reached or imagined reaching to one of three targets placed at different distances from a start position. Both executed and imagined movement times scaled with target distance, and they were highly correlated, confirming previous work and suggesting that participants did imagine the respective movement. Increased pupillary dilation was evident during motor execution compared to rest, with stronger dilations for larger movements. Pupil dilations also occurred during motor imagery, however they were generally weaker than during motor execution and they were not influenced by imagined movement distance. Instead, dilations during motor imagery resembled pupil responses obtained during a non-motor imagery task (imagining a previously viewed painting). Our results demonstrate that pupillary responses can reliably capture the dynamics of an executed goal-directed reaching movement, but suggest that pupillary responses during imagined reaching movements reflect general cognitive rather than motor-specific components of the motor imagery process. New and noteworthyPupil size is influenced by the performance of cognitive tasks. Here we demonstrate that pupil size increases during execution and mental simulation of goal-directed reaching movements compared to rest. Pupil dilations scale with movement amplitude only during motor execution, whereas they are similar during motor imagery and a non-motor imagery, cognitive task.

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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↗

bioRxiv2021

Tactile suppression stems from sensation-specific sensorimotor predictions

The ability to sample sensory information with our hands is crucial for smooth and efficient interactions with the world. Despite this important role of touch, tactile sensations on a moving hand are perceived weaker than when presented on the same but stationary hand.1-3 This phenomenon of tactile suppression has been explained by predictive mechanisms, such as forward models, that estimate future sensory states of the body on the basis of the motor command and suppress the associated predicted sensory feedback.4 The origins of tactile suppression have sparked a lot of debate, with contemporary accounts claiming that suppression is independent of predictive mechanisms and is instead akin to unspecific gating.5 Here, we target this debate and provide evidence for sensation-specific tactile suppression due to sensorimotor predictions. Participants stroked with their finger over textured surfaces that caused predictable vibrotactile feedback signals on that finger. Shortly before touching the texture, we applied external vibrotactile probes on the moving finger that either matched or mismatched the frequency generated by the stroking movement. We found stronger suppression of the probes that matched the predicted sensory feedback. These results show that tactile suppression is not limited to unspecific gating but is specifically tuned to the predicted sensory states of a movement.

neuroscience↗

bioRxiv2021

Friction is preferred over grasp configuration in precision grip grasping

How humans visually select where to grasp an object depends on many factors, including grasp stability and preferred grasp configuration. We examined how endpoints are selected when these two factors are brought into conflict: Do people favor stable grasps or do they prefer their natural grasp configurations? Participants reached to grasp one of three cuboids oriented so that its two corners were either aligned with, or rotated away from, each individuals natural grasp axis (NGA). All objects were made of brass (mass: 420 g) but the surfaces of their sides were manipulated to alter friction: 1) all-brass, 2) two opposing sides covered with wood, while the other two remained of brass, or 3) two opposing sides covered with sandpaper, and the two remaining brass sides smeared with vaseline. Grasps were evaluated as either clockwise (thumb to the left of finger in frontal plane) or counterclockwise of the NGA. Grasp endpoints depended on both object orientation and surface material. For the all-brass object, grasps were bimodally distributed in the NGA-aligned condition but predominantly clockwise in the NGA-unaligned condition. These data reflected participants natural grasp configuration independently of surface material. When grasping objects with different surface materials, endpoint selection changed: Participants sacrificed their usual grasp configuration to choose the more stable object sides. A model in which surface material shifts participants preferred grip angle proportionally to the perceived friction of the surfaces accounts for our results. Our findings demonstrate that a stable grasp is more important than a biomechanically comfortable grasp configuration. NEW & NOTEWORTHYWhen grasping an object, humans can place their fingers at several positions on its surface. The selection of these endpoints depends on many factors, with two of the most important being grasp stability and grasp configuration. We put these two factors in conflict and examine which is considered more important. Our results highlight that humans are not reluctant to adopt unusual grasp configurations in order to satisfy grasp stability.

neuroscience↗

bioRxiv2019

Reaching around obstacles accounts for uncertainty in coordinate transformations

When reaching to a visual target, humans need to transform the spatial target representation into the coordinate system of their moving arm. It has been shown that increased uncertainty in such coordinate transformations, for instance when the head is rolled toward one shoulder, leads to higher movement variability and influence movement decisions. However, it is unknown whether the brain incorporates such added variability in planning and executing movements. We designed an obstacle avoidance task in which participants had to reach with or without visual feedback of the hand to a visual target while avoiding collisions with an obstacle. We varied coordinate transformation uncertainty by varying head roll (straight, 30{degrees} clockwise and 30{degrees} counterclockwise). In agreement with previous studies, we observed that the reaching variability increased when the head was tilted. Indeed, head roll did not influence the number of collisions during reaching compared to the head straight condition, but it did systematically change the obstacle avoidance behavior. Participants changed the preferred direction of passing the obstacle and increased the safety margins indicated by stronger movement curvature. These results suggest that the brain takes the added movement variability during head roll into account and compensates for it by adjusting the reaching trajectories.

neuroscience↗