Biology subjects

Gomi, H.

Publications and source records attributed to Gomi, H..

11 recordsLinked to original sources

bioRxiv2025

Eye-hand coordination beyond vision: preceding gaze history shapes reaching memories

Skilled reaching behaviors, such as grasping a cup or catching a ball, require adaptive changes in response to error signals. In natural behavior, reaches are typically coordinated with preceding eye movements toward the target. Despite this behavioral relevance, the potential linkage between preceding eye movements themselves, rather than static gaze positions, and memory formation for reaching has been largely overlooked. Here, we used a visuomotor rotation task to investigate how recent dynamic gaze states contribute to the formation and retrieval of reaching memories. We show that, in the learning of two conflicting visuomotor maps that would normally interfere with one another (namely, clockwise and counterclockwise rotation), not only the static spatial relationship between the gaze and the target but also the dynamic state of the eye movements themselves can serve as contextual cues that enable learning. We further show that the generalization pattern of reach learning across different gaze conditions can be explained by the gaze states distance computed with temporal weighting. These findings indicate that reaching memories are encoded in tight association with the recent history of preceding gaze states. Our results expand the functional role of eye-hand coordination beyond visual guidance, revealing its importance in orchestrating flexible motor learning. Significant StatementIn everyday behavior, goal-directed arm movements are typically preceded by eye movements, and eye-hand coordination has been regarded mainly as a functional mechanism for visual guidance of action. This study expands that view by showing that preceding gaze states also shape how the brain learns and retrieves motor memories of reaches. We demonstrate that conflicting visuomotor maps, which are usually difficult to learn because of memory interference, can be learned simultaneously when they are associated with different preceding eye movements. Furthermore, generalization experiments show that reach learning depends on the recent history of gaze states within a brief time window before reach onset. These findings indicate that preceding gaze history plays a significant role in shaping flexible reach memories.

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bioRxiv2024

15 second assessment of hand and foot motor skill using a smartphone

Motor skills are essential for daily functioning and serve as key indicators of healthy development and aging. However, existing assessments of motor skill are inaccessible to the public and do not directly measure the quality of the movement. Here, we developed a convenient and robust measure of motor skill that uses a smartphone app to provide on-the-spot assessment in just 15 seconds. To validate our method, we asked 1675 participants between the ages of three to eighty-eight years old to trace circles at a fixed rhythm with a smartphone, which was either held in the hand or strapped to the ankle. Motor skill was quantified by the smartphone app using an algorithm that calculated the variability in the accelerations trajectory. Our assessment revealed significant changes in the skill of the hands and feet with age and practice. The variability of the hands and feet linearly decreased and matured in the mid-teens, but it regressed gradually thereafter. Laterality, or the difference in the motor skill between the left and right limbs, increased with age as the non-dominant hand and foot regressed faster in the elderly. Motor practice affected both skill and laterality as left-handers who were forced to write with their right-hand during childhood had a tell-tale sign of stronger right-handedness and, surprisingly, right-footedness. Our assessment aims to democratize motor skill assessment, making it accessible for professionals and users of all ages.

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bioRxiv2024

Minimizing command timing volatility is a key factor in skilled actions

Variability between movements prevents the best athletes from making a perfect shot every time. While fluctuations in the amplitude of neural sensory inputs and motor outputs are thought to be primarily responsible, they only account for a fraction of the observed variability. Here, we propose that a significant portion of the variability is due to imprecisely timed motor commands. This command timing volatility theory best explained the three peaks observed in the force variabilitys time-series in discrete reaching movements and during periodic force control. Furthermore, we show how the timing volatility in the non-dominant arms muscles is larger than in the dominant arm, then develop a variability index that estimates the arms timing volatility via its variability during circle tracing. The difference in the variability index between the left and right hands accurately predicts the Edinburgh Quotient, suggesting a relationship between handedness and the command timing volatility of the left- and right-hands. Lastly, we constructed a simulation of reaching movements made by an arm controlled by muscles whose command timing was made incrementally more volatile. As timing volatility increased, aiming became less precise and movements jerkier. Such impairments during reaching are reported in patients with different neuronal diseases that damage any brain regions critical to motor timing, suggesting that essential aspects of these symptoms may be caused by excessive timing volatility. Our theory provides a unifying computational perspective of movement variability in healthy and diseased individuals that is essential to understanding the control of movements.

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bioRxiv2023

Modulation of somatosensory signal transmission in the primate cuneate nucleus during voluntary hand movement

Successful extraction of tactile and kinematic information is crucial for appropriate motor actions in daily life. To achieve this objective, sensory signals should be effectively regulated during motor actions. This regulation is understood both empirically and conceptually, but it is not well known where and how it is implemented in the central nervous system. Here, we show that, during voluntary movement, sensory signals are already attenuated in the primate cuneate nucleus, an early processing site in the ascending lemniscus pathway. The degree of suppression was comparable with the one reported in the cortex, suggesting that psychological attenuation of somatosensation could be ascribed to the cuneate. The results also revealed that this sensory attenuation was of descending origin, suggesting that cortical sensory prediction signals could regulate cuneate sensory transmission for extracting meaningful, and attenuate unnecessary, signals for movement regulation. This recurrent sensory modulation mechanism between cortical and subcortical areas may generalize to other sensory modalities and cognitive processes.

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bioRxiv2023

Active self-touch restores bodily self-awareness following disruption by the rubber hand illusion

Bodily self-awareness relies on a constant integration of visual, tactile, proprioceptive, and motor signals. In the "Rubber Hand Illusion" (RHI), conflicting visuo-tactile stimuli lead to changes in self- awareness. It remains unclear whether other, somatic signals could compensate for the alterations in self-awareness caused by visual information about the body. Here, we used the RHI in combination with robot-mediated self-touch to systematically investigate the role of tactile, proprioceptive, and motor signals in protecting and restoring bodily self-awareness. Participants moved the handle of a leader robot with their right hand and simultaneously received corresponding tactile feedback on their left hand from a follower robot. This self-touch stimulation was performed either before or after the induction of a classical RHI. Across three experiments, active self-touch delivered after - but not before - the RHI, significantly reduced the proprioceptive drift caused by RHI, supporting a restorative role of active self-touch on bodily self-awareness. The effect was not present during involuntary self-touch, where the participants hand was passively moved, suggesting that the restorative effect depends on the presence of a voluntary motor command, and that synchrony of bilateral sensory events is insufficient. Unimodal control conditions confirmed that the coordination of both tactile and motor components of self-touch was necessary to restore bodily self-awareness. These results suggest that voluntary self-touch can restore an intrinsic representation of the body following visual capture during RHI.

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bioRxiv2022

A model predictive control strategy to regulate movements and interactions

Humans are adept at moving the arm to interact with objects and surfaces. The brain is thought to regulate motion and interactions using two different controllers, one specialized for movements and the other for force regulation. However, it remains unclear whether different control mechanisms are necessary. Here we show that the brain can employ a single high-level control strategy for both movement and interaction control. The Model Predictive Control (MPC) strategy introduced in this paper uses an internal model of the environment to plan the arms muscle activity whilst updating its predictions using periodic feedback. Computer simulations demonstrate MPCs ability to produce human-like movements and after-effects in free and force field environments. It can simultaneously regulate both force and stiffness during interactions, and can accomplish motor tasks demanding transitions between motion and interaction control. Model Predictive Control promises to be an important tool to test ideas of motor control as it can handle nonlinear dynamics with changing environments and goals without having to specify the movement duration.

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bioRxiv2021

Neural dynamics of illusory tactile pulling sensations

The sensation of directional forces and their associated sensorimotor commands are inextricably intertwined, complicating the identification of brain circuits responsible for tactile pulling sensations. One hypothesis is that, like tactile frequency discrimination, pulling sensations are generated by early sensory-frontal activity. Alternatively, they may be generated later in the somatosensory association cortex. To dissociate these accounts and uncouple the pulling sensation from unrelated but correlated sensory and motor processing, we combined high-density EEG with an oddball paradigm and asymmetric vibration, which creates an illusory sensation of the hand being directionally pulled. Oddballs that created a pulling sensation in the opposite direction to common stimuli were compared to the same oddballs in the context of neutral common stimuli (symmetric vibration) and to neutral oddballs. Brain responses to having directional pulling expectations violated by directional stimuli were therefore isolated. Contrary to the sensory-frontal account, frontal N140 brain activity was actually larger for neutral than pulling oddballs. Instead, pulling sensations were associated with amplitude and latency modulations of midline P200 and P3b potentials, and specifically, to contralateral parietal lobe activity 280ms post-stimulus. The timing of this activity suggested pulling sensations involve spatial processing, such as tactile remapping between coordinate frames. Source localization showed this activity to be centered on the postcentral sulcus, superior parietal lobule and intraparietal sulcus, suggesting that pulling sensations arise via the processing of body position, tactile orientation and peripersonal space. Our results demonstrate how tactile illusions can uniquely disambiguate parietal contributions to somatosensation by removing unrelated sensory processing. Significance statementThe neural mechanisms of tactile pulling sensations are poorly understood. Competing early sensory-frontal and later somatosensory association cortex accounts are hard to dissociate due to confounding sensory and motor signals present when forces are applied to the skin. Here, we used EEG and a novel asymmetric vibration approach to induce an illusory pulling sensation, which circumvents these issues. We found that pulling sensations were associated with parietal lobe activity 280ms post-stimulus and modulations of the P200. The timing and location of this activity suggested that pulling sensations necessitate spatial processing and supported a somatosensory association cortex account of the pulling sensation.

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bioRxiv2021

Intermanual transfer of visuomotor learning is facilitated by a cognitive strategy

Humans continuously adapt their movement to a novel environment by recalibrating their sensorimotor system. Recent evidence, however, shows that explicit planning to compensate for external changes, i.e. a cognitive strategy, can also aid performance. If such a strategy is indeed planned in external space, it should improve performance in an effector independent manner. We tested this hypothesis by examining whether promoting a cognitive strategy during a visual-force adaptation task performed in one hand can facilitate learning for the opposite hand. Participants rapidly adjusted the height of visual bar on screen to a target level by isometrically exerting force on a handle using their right hand. Visuomotor gain increased during the task and participants learned the increased gain. Visual feedback was continuously provided for one group, while for another group only the endpoint of the force trajectory was presented. The latter has been reported to promote cognitive strategy use. We found that endpoint feedback produced stronger intermanual transfer of learning and slower response times than continuous feedback. In a separate experiment, we confirmed that the aftereffect is indeed reduced when only endpoint feedback is provided, a finding that has been consistently observed when cognitive strategies are used. The results suggest that intermanual transfer can be facilitated by a cognitive strategy. This indicates that the behavioral observation of intermanual transfer can be achieved either by forming an effector-independent motor representation, or by sharing an effector-independent cognitive strategy between the hands. New and noteworthyThe causes and consequences of cognitive strategy use for motor learning are poorly understood. We tested whether a visuomotor task learned using a strategy generalizes across effectors. Visual feedback was manipulated to enhance the use of a cognitive strategy. Learning using a cognitive strategy for one hand transferred to the task performed by the un-learned hand. Our result suggests that intermanual transfer can also result from a common cognitive strategy used to control both hands.

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bioRxiv2021

Sensory and cognitive factors affecting multi-digit touch: a perceptual and modeling study

Whilst everyday interactions with objects often involve multiple tactile contacts, integration of tactile signals remains poorly understood. Here we characterise the integration process of tactile motion on multiple fingerpads. Across four experiments, participants averaged the direction of two simultaneous tactile motion trajectories delivered to different fingerpads. Averaging performance differed between within- and between-hands in terms of sensitivity and precision but was unaffected by somatotopic proximity between stimulated fingers. The sensitivity to the average direction was influenced by the discrepancy between individual motion signals, but only for within-hand conditions. This was explained by a model, in which the virtually leading finger received a higher perceptual weighting. Precision was greater in between-hand compared to within-hand conditions. While biased weighting accounted for differences in sensitivity, it was not sufficient to explain the difference in precision, implying additional sensory limitations during within-hand integration. We suggest that unimanual integration is limited and thus exploits a natural cognitive prior involving a single object moving relative to the hand to maximise information gain. Author summaryTactile stimulation is always on. Yet little is known about how the brain combines widespread tactile inputs for perception. Most tactile studies emphasize a single point of tactile stimulation (e.g., location or intensity of a static stimulus) and minimal units of tactile perception (e.g., acuity or selectivity). However, our daily interactions with the world involve encoding spatially and temporally extended tactile signals. Perceiving tactile objects and events as coherent entities requires the somatosensory system to aggregate tactile afferent signals across separate skin regions (i.e., separate digits). Across four experiments we asked participants to average direction of two tactile motion trajectories delivered simultaneously to two different fingerpads, either on the same, or on different hands. Our results show strong integration between multiple tactile inputs, but subject to limitations for inputs delivered within a hand. Our model suggests that tactile inputs are weighted according to an integrative model of hand-object interaction that operates within-hands on purely geometric information to prioritise novel information from a virtually leading finger (VLF).

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bioRxiv2020

Constructing spatial perception through self-touch

Classical accounts of spatial perception are based either on the topological layout of sensory receptors, or on implicit spatial information provided by motor commands. In everyday self-touch, as when stroking the left arm with the right hand, these elements are inextricably linked, meaning that tactile and motor contributions to spatial perception cannot readily be disentangled. Here, we developed a robot-mediated form of self-touch in order to decouple the spatial extent of active or passive movements from their tactile consequences. Participants judged the spatial extent of either the movement of the right hand, or of the resulting tactile stimulation to their left forearm. Across five experiments, we found bidirectional interference between motor and tactile information. Crucially, both directions of interference were stronger during active than passive movements. Thus, voluntary motor commands produced stronger integration of multiple signals relevant to spatial perception.

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bioRxiv2020

Somatosensory evoked potentials indexing lateral inhibition are modulated according to the mode of perceptual processing: comparing or combining multi-digit tactile motion

Many perceptual studies focus on the brains capacity to discriminate between stimuli. However, our normal experience of the world also involves integrating multiple stimuli into a single perceptual event. Neural circuit mechanisms such as lateral inhibition are believed to enhance local differences between sensory inputs from nearby regions of the receptor surface. However, this mechanism would seem dysfunctional when sensory inputs need to be combined rather than contrasted. Here, we investigated whether the brain can strategically regulate the strength of suppressive interactions that underlie lateral inhibition between finger representations in human somatosensory processing. To do this, we compared sensory processing between conditions that required either comparing or combining information. We delivered two simultaneous tactile motion trajectories to index and middle fingertips of the right hand. Participants had to either compare the directions of the two stimuli, or to combine them to form their average direction. To reveal preparatory tuning of somatosensory cortex, we used an established event-related potential design to measure the interaction between cortical representations evoked by digital nerve shocks immediately before each tactile stimulus. Consistent with previous studies, we found a clear suppressive interaction between cortical activations when participants were instructed to compare the tactile motion directions. Importantly, this suppressive interaction was significantly reduced when participants had to combine the same stimuli. These findings suggest that the brain can strategically switch between a comparative and a combinative mode of somatosensory processing, according to the perceptual goal, by preparatorily adjusting the strength of a process akin to lateral inhibition.

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