Biology subjects

Kurtzer, I.

Publications and source records attributed to Kurtzer, I..

6 recordsLinked to original sources

bioRxiv2026

Aging selectively impairs how peripheral vision calibrates anticipatory postural responses to object motion

Anticipatory postural adjustments (APAs) scale with velocity of approaching objects, with scaling magnitude depending on whether the moving object is actively foveated and tracked, processed through fixated peripheral vision, or processed through fixated central vision. Aging preferentially degrades the magnocellular pathway underlying peripheral motion processing while sparing the extraretinal signals available during smooth pursuit. We therefore asked whether the effect of aging on velocity-dependent APA scaling differs across these three visual pathways. Eighteen young and eighteen older adults stopped a virtual object approaching at four velocities (15-33 cm/s) under three gaze conditions: active foveation via smooth pursuit, central fixation, and peripheral fixation. We measured peak anticipatory force, rate of force development, and time to contact at force onset. Despite reduced smooth pursuit gain in older adults, velocity-dependent scaling was equivalent between age groups during active foveation, and minimal in both groups during central fixation. Critically, young adults scaled force rate during peripheral fixation nearly as steeply as during active foveation, whereas older adults slope was significantly lower -- a difference not observed during the other gaze conditions. Older adults achieved comparable peak force by initiating responses earlier. These results establish that age-related decline in anticipatory motor control is pathway-specific: aging selectively impairs peripheral motion processing for APAs, while extraretinal mechanisms remain capable of sustaining velocity-dependent scaling. More broadly, peripheral motion processing emerges as a candidate physiological locus of age-related postural vulnerability, raising the question of whether magnocellular-targeted training can restore APA scaling in older adults. Key PointsO_LIYoung and older adults stopped virtual objects under three visual conditions: active foveation via smooth pursuit eye movements, and stationary gaze with the object moving through either central or peripheral vision. C_LIO_LIVelocity-dependent force rate scaling was preserved during active foveation in both age groups, minimal during fixated central vision in both age groups, and selectively impaired in older adults during fixated peripheral vision. C_LIO_LIWe found an age-induced vulnerability in peripheral visual motion processing for anticipatory posture stabilization. C_LI

neuroscience↗

bioRxiv2025

Smooth pursuit eye movements contribute to long-latency reflex modulation in the lower extremity

Somatosensory mediated reactions play a fundamental role in adapting to environmental changes, particularly through long-latency responses (LLRs)--rapid corrective muscle responses (50-100ms) following limb perturbations that account for limb biomechanics and task goals. We investigated how smooth pursuit eye movements (SPEM), which are slow eye movements used to track moving objects, influence LLRs of the upper and lower limb during mechanical interactions with moving objects. In the first experiment, participants stood and stabilized their arm against a colliding virtual object. This occurred while subjects either visually pursued the moving object or fixated a central location. The robot occasionally applied a mechanical perturbation to the arm either 200ms or 60ms before the anticipated collision. As in previous studies, LLRs were observed in leg muscles to a perturbation of the upper limb. Moreover, leg LLRs were modulated by gaze, being larger during pursuit than fixation but only during the late perturbations. This timing-specific modulation aligns with previous reports of policy transitions in feedback control roughly 60ms before impact. Upper limb LLRs were not significantly impacted by gaze. This lack of modulation could reflect the context of upright stance, so we conducted a second experiment which was the same in all ways except that the subjects remained seated. Again, the upper limb LLRs were not impacted by gaze. The selective impact of gaze modulation on stance control highlights the sophisticated nature of coordinating eye movements, arm control, and whole-body postural responses. NEW and NOTEWORTHYSmooth pursuit eye movements are used to track moving objects. We show for the first time that smooth pursuit eye movements contribute to modulation of long-latency reflexes in the lower limb during virtual object interactions in upright stance. These findings suggest a neurophysiological link between predictive control of eye movements and feedback control of upright stance.

neuroscience↗

bioRxiv2024

Predictive posture stabilization before contact with moving objects: equivalence of smooth pursuit tracking and peripheral vision

Postural stabilization is essential to effectively interact with our environment. Humans preemptively adjust their posture to counteract impending disturbances, such as those encountered during interactions with moving objects, a phenomenon known as anticipatory postural adjustments (APAs). APAs are thought to be influenced by predictive models that incorporate object motion via retinal motion and extra-retinal signals. Building on our previous work that examined APAs in relation to the perceived momentum of moving objects, here we explored the impact of object motion within different visual field sectors on the human capacity to anticipate motion and prepare APAs for contact between virtual moving objects and the limb. Participants interacted with objects moving towards them under different gaze conditions. In one condition, participants fixated on either a central point (central fixation) or left-right of the moving object (peripheral fixation), while in another, they followed the moving object with smooth pursuit eye movements (SPEM). We found that APAs had the smallest magnitude in the central fixation condition and that no notable differences in APAs were apparent between the SPEM and peripheral fixation conditions. This suggests that the visual system can accurately perceive motion of objects in peripheral vision for posture stabilization. Using Bayesian Model Averaging, we also evaluated the contribution of different gaze variables, such as eye velocity and gain (ratio of eye and object velocity) and showed that both eye velocity and gain signals were significant predictors of APAs. Taken together, our study underscores the roles of oculomotor signals in modulation of APAs. New and NoteworthyWe show that the human visuomotor system can detect motion in peripheral vision and make anticipatory adjustments to posture before contact with moving objects, just as effectively as when the eye movement system tracks those objects through smooth pursuit eye movements. These findings pave the way for research into how age-induced changes in spatial vision, eye movements, and motion perception could affect the control of limb movements and postural stability during motion-mediated interactions with objects.

neuroscience↗

bioRxiv2023

Smooth pursuit eye movements contribute to anticipatory force control during mechanical stopping of moving objects

When stopping a closing door or catching an object, humans process the motion of inertial objects and apply reactive limb force over short period to interact with them. One way in which the visual system processes motion is through extraretinal signals associated with smooth pursuit eye movements (SPEM). We conducted three experiments to investigate how SPEM contribute to anticipatory and reactive hand force modulation when interacting with a virtual object moving in the horizontal plane. We hypothesized that SPEM signals are critical for timing motor responses, anticipatory control of hand force, and task performance. Participants held a robotic manipulandum and attempted to stop an approaching simulated object by applying a force impulse (area under force-time curve) that matched the objects virtual momentum upon contact. We manipulated the objects momentum by varying either its virtual mass or its speed under free gaze or constrained gaze conditions. We examined gaze variables, timing of hand motor responses, anticipatory force control, and overall task performance. Our results show that when SPEM were constrained, anticipatory modulation of hand force prior to contact decreased. However, constraining SPEM did not seem to affect the timing of the motor response or the task performance. Together, these results suggest that SPEM may be important for anticipatory control of hand force prior to contact and may also play a critical role in anticipatory stabilization of limb posture when humans interact with moving objects. New and NoteworthyWe show for the first time that smooth pursuit eye movements (SPEM) play a role in modulation of anticipatory control of hand force to stabilize posture against contact forces. SPEM are critical for tracking moving objects, facilitate processing motion of moving objects, and are impacted during aging and in many neurological disorders, such as Alzheimers disease and Multiple Sclerosis. These results provide a novel basis to probe how changes in SPEM could contribute to deficient limb motor control in older adults and patients with neurological disorders.

neuroscience↗

bioRxiv2021

Object motion kinematics influence both feedforward and feedback motor responses during virtual catching

An important window into sensorimotor function is how humans interact and stop moving projectiles, such as stopping a door from closing shut or catching a ball. Previous studies have suggested that humans time the initiation and modulate the amplitude of their muscle activity based on the momentum of the approaching object. However, real-world experiments are constrained by laws of mechanics, which cannot be manipulated experimentally to probe the mechanisms of sensorimotor control and learning. An augmented-reality variant of such tasks allows for experimental manipulation of the relationship between motion and force to obtain novel insights into how the nervous system prepares motor responses to interact with moving stimuli. Existing paradigms for studying interactions with moving projectiles use massless object and are primarily focused on quantifying gaze and hand kinematics. Here, we developed a novel collision paradigm using a robotic manipulandum where participants mechanically stopped a virtual object moving in the horizontal plane. On each block of trials, we varied the virtual objects momentum by increasing either its speed or mass. Participants stopped the object by applying a force impulse that matched the object momentum. We observed that arm force increased as a function of object momentum linked to changes in virtual mass or speed, mirroring results from studies involving catching free-falling objects. In addition, increasing object speed resulted in later onset of hand force relative to the impending time-to-contact. These findings show that the present paradigm can be used to determine how humans process projectile motion for hand motor control.

neuroscience↗

bioRxiv2021

Age-related deficits in rapid visuomotor decision-making

Many goal-directed actions that require rapid visuomotor planning and perceptual decision-making are affected in older adults, causing difficulties in execution of many functional activities of daily living. Visuomotor planning and perceptual decision-making are mediated by the dorsal and ventral visual streams, respectively, but it is unclear how age-induced changes in sensory processing in these streams contribute to declines in goal-directed actions. Previously, we have shown that in healthy adults task demands affect the integration of sensory information between the two streams and more motorically demanding tasks induce earlier decisions and more decision errors. Here, we asked the question if older adults would exhibit larger declines in interactions between the two streams during demanding motor tasks. Older adults (n=15) and young controls (n=26) performed a simple reaching task and a more demanding interception task towards virtual objects. In some blocks of trials, participants also had to select an appropriate movement based on the shape of the object. Our results showed that older adults made a similar number of initial decision errors during both the reaching and interception tasks but corrected fewer of those errors during movement. During the more demanding interception decision task, older adults made more decision- and execution-related errors than young adults, which were related to early initiation of their movements. Together, these results suggest that older adults have a reduced ability to integrate new perceptual information to guide online action, which may reflect impaired ventral-dorsal stream interactions. HighlightsO_LIOlder adults showed reduced performance in a visuomotor decision-making task C_LIO_LIInitial decision errors were similar between young and older adults C_LIO_LIOlder adults were less likely to correct initial decision errors C_LIO_LIMore demanding movements were associated with earlier and less accurate decisions C_LI

neuroscience↗