Biology subjects

Nisky, I.

Publications and source records attributed to Nisky, I..

14 recordsLinked to original sources

bioRxiv2023

Exploring the Relation Between Stiffness Perception and Action Using Models and Artificial Neural Networks

We use sensory feedback to form our perception, and control our movements and forces (actions). There is an ongoing debate about the relation between perception and action, with evidence in both directions. For example, there are cases in which perceptual illusions affect action signals and cases where they do not. However, even when they do, it is unknown if perceptual information can be inferred from action signals alone. To answer this question, we utilized a perceptual illusion created by artificial tactile skin stretch, which increases stiffness perception, and affects grip force. We used data recorded in a stiffness discrimination task in which participants compared pairs of virtual objects, comprised of force and artificial skin stretch and indicated which they perceived as stiffer. We explored if models could predict participants' perceptual responses, and the increase in stiffness perception caused by the skin stretch, solely from their recorded action signals. That is, with no information provided about the stimuli. We found that participants' perceptual augmentation could be predicted to an extent from their action signals alone. We predicted the average augmentation effect across participants, and a general trend of increased predicted perceptual augmentation for increased real perceptual augmentation. These results indicate that at least some perceptual information is present in action signals. Furthermore, of the action signals examined, grip force was necessary for predicting the augmentation effect, and a motion signal (e.g., position) was needed for predicting human-like perception, shedding light on what information may be present in the different signals.

neuroscience↗

bioRxiv2023

Artificial Tactile Stimulation Provides Haptic Cuing in Force Field Adaptation

When interacting with objects with unfamiliar dynamics, the sensorimotor system uses haptic information to develop internal representations of the new dynamics. These representations are subsequently used to manipulate the objects by applying predictive forces that comply with the mechanical properties of the objects. In a recent study (Farajian et al. 2020), we showed that when participants evaluated the stiffness of elastic objects, adding artificial tactile stimulation created an illusion of higher stiffness, increasing the grip force control used to interact with the object. Here, we took a step further in understanding how kinesthetic and tactile information is integrated into the control of objects. Specifically, we examined how added skin stretch influenced the learning of novel forces. We found that the extent of force compensation that the participants exhibited depended on the direction of the artificial skin stretch applied simultaneously with the force; learning was enhanced when the skin was stretched in the opposite direction to the external force and diminished when the skin was stretched in the same direction. Strikingly, when the skin stretch stimulation was delivered during probe trials in which the force perturbation was absent, the behavior pattern was flipped, with an increase in force compensation for the same-direction skin stretch stimulation and vice versa. Modeling suggests that these results reflect a unique effect of tactile stimulation during the learning of novel forces; rather than becoming integrated with the dynamic information, it is used by the sensorimotor system as a guidance cue, possibly through explicit mechanisms, providing information on the way to compensate for the forces and optimize movements. We believe that these findings propose a novel instructive role of tactile stimulation during interaction with a dynamic object. This provides a significant potential to leverage these effects in the development of devices aiming to assist and guide users in many human-in-the-loop applications, such as rehabilitation and surgical robotics.

neuroscience↗

bioRxiv2023

Direction-Specific Effects of Artificial Skin-Stretch on Stiffness Perception and Grip Force Control

When interacting with an object, we use kinesthetic and tactile information to create our perception of the objects properties and to prevent its slippage using grip force control. We previously showed that applying artificial skin-stretch together with, and in the same direction as, kinesthetic force increases the perceived stiffness. Here, we investigated the effect of the direction of the artificial stretch on stiffness perception and grip force control. We presented participants with kinesthetic force together with negative or positive artificial stretch, in the opposite or the same direction of the natural stretch due to the kinesthetic force, respectively. Our results showed that artificial skin-stretch in both directions augmented the perceived stiffness; however, the augmentation caused by the negative stretch was consistently lower than that caused by the positive stretch. Additionally, we proposed a computational model that predicts the perceptual effects based on the preferred directions of the stimulated mechanoreceptors. When examining the grip force, we found that participants applied higher grip forces during the interactions with positive skin-stretch in comparison to the negative skin-stretch, which is consistent with the perceptual results. These results may be useful in tactile technologies for wearable haptic devices, teleoperation, and robot-assisted surgery.

neuroscience↗

bioRxiv2022

Orientation control strategies and adaptation to a visuomotor perturbation in rotational hand movements

Computational approaches to biological motor control are used to discover the building blocks of human motor behavior. Models explaining features of human hand movements have been studied thoroughly, yet only a few studies attempted to explain the control of the orientation of the hand; instead, they mainly focus on the control of hand translation, predominantly in a single plane. In this study, we aimed to establish a basic understanding of the way humans control the orientation of their hands. We developed a quaternion-based score that quantifies the geodicity of rotational hand movements and evaluated it experimentally. In the first experiment participants performed a simple orientation-matching task with a robotic manipulator. We found that rotations are generally performed by following a geodesic in the quaternion hypersphere, which suggests that, similarly to translation, the orientation of the hand is centrally controlled. We also established a baseline for the study of human response to perturbed visual feedback of the orientation of the hand. In the subsequent second experiment we studied the adaptation of participants to visuomotor rotation that is applied on the hands rotation, and the transfer of the adaptation to a different initial orientation. We observed partial adaptation to the perturbation. The patterns of the transfer of the adaptation to a different initial orientation were consistent with the representation of the orientation in extrinsic coordinates. The results of the two experiments raise questions regarding the nature of central control of hand orientation. Discussion and intuitions from these results can be of benefit for many applications that involve fine manipulation of rigid bodies, such as teleoperation and neurorehabilitation. Author summaryDaily motor actions, as simple as pouring a glass of wine or as complicated as playing a violin, require coordinated activation of multiple muscles that synchronize to produce a precise motion of the hand. Controlled by sensorimotor areas in the central nervous system, our muscles can translate and rotate our hand from one posture to another. Our study focused on the very basis of the control of orientation: we attempted to reveal which variables are centrally controlled when we rotate our hand. The discovery that simple rotations are generally performed along a geometrically optimal path established a baseline for studying the response to rotation-based perturbations. By visually remapping the orientation of the hand, we found that humans perceive their hands orientation in visual, rather than joint-based coordinates. These findings have implications for the design of human-centered control systems for teleoperation, where visual distortions may occur, and for the design of rehabilitation devices for people with motor impairments.

neuroscience↗

bioRxiv2022

A New Power Law Linking the Speed to the Geometry of Tool-Tip Orientation in Teleoperation of a Robot Assisted Surgical System

Fine manipulation is important in dexterous tasks executed via teleoperation, including in robot-assisted surgery. Discovering fundamental laws of human movement can benefit the design and control of teleoperated systems, and the training of their users. These laws are formulated as motor invariants, such as the well-studied speed-curvature power law. However, while the majority of these laws characterize translational movements, fine manipulation requires controlling the orientation of objects as well. This subject has received little attention in human motor control studies. Here, we report a new power law linking the speed to the geometry in orientation control - humans rotate their hands with an angular speed that is exponentially related to the local change in the direction of rotation. We demonstrate this law in teleoperated tasks performed by surgeons using surgical robotics research platforms. Additionally, we show that the laws parameters change slowly with the surgeons training, and are robust within participants across task segments and repetitions. The fact that this power law is a robust motor invariant suggests that it may be an outcome of sensorimotor control. It also opens questions about the nature of this control and how it can be harnessed for better control of human-teleoperated robotic systems.

neuroscience↗

bioRxiv2020

Visual Feedback Weakens the Augmentation of Perceived Stiffness by Artificial Skin Stretch

Tactile stimulation devices are gaining popularity in haptic science and technology - they are lightweight, low-cost, can be easily made wearable, and do not suffer from instability during closed loop interactions with users. Applying tactile stimulation in the form of stretching the skin of the fingerpads, concurrently with kinesthetic force feedback, has been shown to augment the perceived stiffness during interactions with elastic objects. However, all of the studies to date have investigated the perceptual augmentation effects of artificial skin-stretch in the absence of visual feedback. We investigated how visual displacement feedback affects the augmentation of perceived stiffness caused by the skin-stretch. We used a forced-choice paradigm stiffness discrimination task with four different conditions: force feedback, force feedback with artificial skin-stretch, force and visual feedback, and force and visual feedback with artificial skin-stretch. We found that visual displacement feedback weakens the skin-stretch induced perceptual augmentation and improves the stiffness discrimination sensitivity.

bioengineering↗

bioRxiv2020

The Effect of Between-Probe Variability in Haptic Feedback on Stiffness Perception and Grip Force Adjustment

When interacting with objects, haptic information is used to create perception of the object stiffness and to regulate grip force. Studies have shown that introducing noise into sensory inputs can create uncertainty in those sensory channels, yet a method of creating haptic uncertainty without distorting the haptic information has yet to be discovered. Toward this end, we investigated the effect of between-probe haptic variability on stiffness perception and grip force control. In a stiffness discrimination task, we added different levels of between-probe haptic variability by changing the stiffness of the force fields between consecutive probes. Unlike the low and high variability levels, the medium level created perceptual haptic uncertainty. Additionally, we ascertained that participants calculated a weighted average of the different stiffness levels applied by a given force field. Examining participants grip force showed that the modulation of the grip force with the load force decreased with repeated exposure to the force field, whereas no change in the baseline was observed. These results were observed in all the variability levels and suggest that between-probe variability created haptic uncertainty that affected the grip force control. Overall, the medium variability level can be effective in inducing uncertainty in both perception and action.

neuroscience↗

bioRxiv2018

The Effect of Dissociation between Proprioception and Vision on Perception and Grip Force Control in a Stiffness Judgment Task

Our sensorimotor system estimates stiffness to form stiffness perception, such as for choosing a ripe fruit, and to generate actions, such as to adjust grip force to avoid slippage of a scalpel during surgery. We examined how temporal manipulation of the haptic and visual feedback affect stiffness perception and grip force adjustment during a stiffness discrimination task. We used delayed force feedback and delayed visual feedback to break the natural relations between these modalities when participants tried to choose the harder spring between pairs of springs. We found that visual delay caused participants to slightly overestimate stiffness while force feedback delay caused a mixed effect on perception; for some it caused underestimation and for some overestimation of stiffness. Interestingly and in contrast to previous findings without vision, we found that participants increased the magnitude of their applied grip force for all conditions. We propose a model that suggests that this increase was a result of coupling the grip force adjustment to their proprioceptive hand position, which was the only modality which we could not delay. Our findings shed light on how the sensorimotor system combines information from different sensory modalities for perception and action. These results are important for the design of improved teleoperation systems that suffer from unavoidable delays.

neuroscience↗

bioRxiv2017

An intermittent control model predicts the triphasic muscles activity during hand reaching

There are numerous ways to reach for an apple hanging from a tree. Yet, our motor system uses a specific muscle activity pattern to generate reaching movements that have similar characteristics. For many decades, we know that this pattern features activity bursts and silent periods. We suggest that these bursts are a strong evidence against the common view that the brain continuously controls the commands to the muscles. Instead, we suggest a model that changes these commands in a discrete way. We use unsupervised machine learning to identify transitions in the state of the muscles, and show that fitting a discrete model to the kinematics of movement using only one parameter predicts the transitions in the state of the muscles. Such discrete controller suggests that the brain reduces the complexity of the motor control problem as well as the wear-and-tear of the muscles by sending commands to the muscles at sparse times. Identifying this discrete controller can be applied in the control of prostheses and physical human-robot interaction systems such as exoskeletons and assistive devices.

neuroscience↗

bioRxiv2017

Stretching the skin of the fingertip creates a perceptual and motor illusion of touching a harder spring

We investigated how artificial tactile feedback in the form of a skin-stretch affects perception of stiffness and grip force adjustment. During interactions with objects, information from kinesthetic and tactile sensors is used to estimate the forces acting on the limbs. These enable the perception of the mechanical properties of objects to form, and the creation of internal models to predict the consequences of interactions with these objects, such as feedforward grip-force adjustments to prevent slippage. Previous studies showed that an artificial stretch of the skin of the fingertips can produce a linear additive effect on stiffness perception, but it remains unclear how such stretch affects the control of grip force. Here, we used a robotic device and a custom-built skin-stretch device to manipulate kinesthetic and tactile information. Using a stiffness discrimination task, we found that adding artificial tactile feedback to a kinesthetic force can create the illusion of touching a harder spring which affects both perception and action. The magnitude of the illusion is linearly related to the amplitude of the applied stretch. We also isolated the contribution of tactile stimulation to the predictive and reactive components of grip force adjustment, and found that unlike in other cases of perceptual illusions, the predictive grip force is modulated consistently with the perceptual tactile-induced illusion. These results have major implications for the design of tactile interfaces across a variety of touch applications such as wearable haptic devices, teleoperations, robot-assisted surgery, and prosthetics.\n\nSignificance StatementSensing forces, using kinesthetic and tactile modalities, is important for assessing the mechanical properties of objects, and for acting the objects while stabilizing grasp against slippage. A major challenge in understanding the internal representations that allow for a predictive grip force control during contact with objects is to dissociate the contribution of tactile and kinesthetic stimuli. To date, this contribution was investigated only in impaired cases either through local anesthesia or in patients with sensory impairment. Our study demonstrates using a programmable mechatronic device that artificially applied skin-stretch creates an illusion of a greater load force that affects grip force control and stiffness perception. These results are applicable in tactile technologies for wearable haptic devices, teleoperation, robot-assisted surgery, and prosthetics.

neuroscience↗

bioRxiv2017

Energy Exchanges at Contact Events Guide Sensorimotor Integration Across Intermodal Delays

One must know the mass of an object to accurately predict how it moves under the effect of an applied force. Similarly, the brain must represent the arms inertia to predict the arms movements elicited by commands impressed upon the muscles. Here, we present evidence suggesting that the integration of sensory information leading to the representation of the arms inertia does not take place continuously in time but only at discrete transient events, in which kinetic energy is exchanged between the arm and the environment. We used a visuomotor delay to induce crossmodal variations in state feedback and uncovered that the difference between visual and proprioceptive velocity estimations at isolated collision events was compensated by a change in the representation of arm inertia. The compensation maintained an invariant estimate across modalities of the expected energy exchange with the environment. This invariance captures different types of dysmetria observed across individuals following prolonged exposure to a fixed intermodal temporal perturbation and provides a new interpretation for cerebellar ataxia.

neuroscience↗

bioRxiv2017

State-Based Delay Representation and Its Transfer from a Game of Pong to Reaching and Tracking

To accurately estimate the state of the body, the nervous system needs to account for delays between signals from different sensory modalities. To investigate how such delays may be represented in the sensorimotor system, we asked human participants to play a virtual pong game in which the movement of the virtual paddle was delayed with respect to their hand movement. We tested the representation of this new mapping between the hand and the delayed paddle by examining transfer of adaptation to blind reaching and blind tracking tasks. These blind tasks enabled to capture the representation in feedforward mechanisms of movement control. A Time Representation of the delay is an estimation of the actual time lag between hand and paddle movements. A State Representation is a representation of delay using current state variables: the distance between the paddle and the ball originating from the delay may be considered as a spatial shift; the low sensitivity in the response of the paddle may be interpreted as a minifying gain; and the lag may be attributed to a mechanical resistance that influences paddles movement. We found that the effects of prolonged exposure to the delayed feedback transferred to blind reaching and tracking tasks and caused participants to exhibit hypermetric movements. These results, together with simulations of our representation models, suggest that delay is not represented based on time, but rather as a spatial gain change in visuomotor mapping.\n\nSignificance StatementIt is known that the brain copes with sensory feedback delays to control movements, but it is unclear whether it does so using a representation of the actual time lag. We addressed this question by exposing participants to a visuomotor delay during a dynamic game of pong. Following the game, participants exhibited hypermetric reaching and tracking movements that indicate that delay is represented as a visuomotor gain rather than as a temporal shift.

neuroscience↗

bioRxiv2017

Smart switching in feedforward control of grip force during manipulation of elastic objects

Switching systems are common in artificial control systems. Here, we suggest that the brain adopts a switched feedforward control of grip forces during manipulation of objects. We measured how participants modulated grip force when interacting with soft and rigid virtual springs when stiffness varied nearly continuously between trials. We identified a sudden phase transition between two forms of feedforward control that differed in the timing of the synchronization between the anticipated load force and the applied grip force. The switch occurred several trials after a threshold stiffness level. These results suggest that in the control of grip force, the brain acts as a switching control system. This opens new research questions as to the nature of the discrete state variables that drive the switching.

neuroscience↗

bioRxiv2017

Adaptation to a Space-variant Visuomotor Delay can Cause Neglect-like Effects on Drawing Symmetry

In daily interactions, our sensorimotor system accounts for spatial and temporal discrepancies between the senses. Functional lateralization between hemispheres causes differences in attention and control of action. In addition, differences in transmission delays between modalities affects motor control. Studies on hemispatial neglect syndrome suggest a link between temporal processing and lateral spatial biases. To understand this link, we studied participants who performed lateral reaching, and adapted to delayed visual feedback in either left, right, or both workspaces. We tested transfer of adaptation to blind drawing, and found that adaptation to left or both delay caused selective leftward elongation. In contrast, adaptation to right delay caused elongation in both directions. Arm dynamics alone cannot explain these findings, but a model of a combined attentional-motor asymmetry across the hemispheres explains our observations. This suggests a possible connection between laterality in delay processing and motor performances observed in cases of hemispatial neglect.

neuroscience↗