Felix Huang - Academia.edu (original) (raw)

Papers by Felix Huang

We explored how the perception of stiffness can be distorted in Minimally Invasive Surgery. We co... more We explored how the perception of stiffness can be distorted in Minimally Invasive Surgery. We combined a mechanical simulator with a haptic device, and implemented linear springs at the tip of the simulated laparoscopic device. To explore the influence of mechanical advantage on perception, we set different values of the ratio between internal and external length of the tool. We found that a nonsymmetrical ratio causes bias in the perceived stiffness when novice tangential probing is compared to radial probing. In contrast, haptic experts did not show similar perceptual bias.

Journal of NeuroEngineering and Rehabilitation, 2020

Background: Clinical practice typically emphasizes active involvement during therapy. However, tr... more Background: Clinical practice typically emphasizes active involvement during therapy. However, traditional approaches can offer only general guidance on the form of involvement that would be most helpful to recovery. Beyond assisting movement, robots allow comprehensive methods for measuring practice behaviors, including the energetic input of the learner. Using data from our previous study of robot-assisted therapy, we examined how separate components of mechanical work contribute to predicting training outcomes. Methods: Stroke survivors (n = 11) completed six sessions in two-weeks of upper extremity motor exploration (selfdirected movement practice) training with customized forces, while a control group (n = 11) trained without assistance. We employed multiple regression analysis to predict patient outcomes with computed mechanical work as independent variables, including separate features for elbow versus shoulder joints, positive (concentric) and negative (eccentric), flexion and extension. Results: Our analysis showed that increases in total mechanical work during therapy were positively correlated with our final outcome metric, velocity range. Further analysis revealed that greater amounts of negative work at the shoulder and positive work at the elbow as the most important predictors of recovery (using cross-validated regression, R 2 = 52%). However, the work features were likely mutually correlated, suggesting a prediction model that first removed shared variance (using PCA, R 2 = 65-85%). Conclusions: These results support robotic training for stroke survivors that increases energetic activity in eccentric shoulder and concentric elbow actions.

ACS Biomaterials Science & Engineering, 2020

The surgical process remains elusive to many. This paper presents two independent empirical inves... more The surgical process remains elusive to many. This paper presents two independent empirical investigations where psychomotor skill metrics were used to quantify elements of the surgical process in a procedural context during surgical tasks in a simulated environment. The overarching goal of both investigations was to address the following hypothesis: Basic motion metrics can be used to quantify specific aspects of the surgical process including instrument autonomy, psychomotor efficiency, procedural readiness, and clinical errors. Electromagnetic motion tracking sensors were secured to surgical trainees' (N = 64) hands for both studies, and several motion metrics were investigated as a measure of surgical skill. The first study assessed performance during a bowel repair and laparoscopic ventral hernia (LVH) repair in comparison to a suturing board task. The second study assessed performance in a VR task in comparison to placement of a subclavian central line. The findings of the first study support our subhypothesis that motion metrics have a generalizable application to surgical skill by showing significant correlations in instrument autonomy and psychomotor efficiency during the suturing task and bowel repair (idle time: r = 0.46, p < 0.05; average velocity: r = 0.57, p < 0.05) and the suturing task and LVH repair (jerk magnitude: r = 0.36, p < 0.05; bimanual dexterity: r = 0.35, p < 0.05). In the second study, performance in VR (steering and jerkiness) correlated to clinical errors (r = 0.58, p < 0.05) and insertion time (r = 0.55, p < 0.05) in placement of a subclavian central line. Both gross (dexterity) and fine motor skills (steering) were found to be important as well as efficiency (i.e., idle time, duration, velocity) when seeking to understand the quality of surgical performance. Both studies support our hypotheses that basic motion metrics can be used to quantify specific aspects of the surgical process and that the use of different technologies and metrics are important for comprehensive investigations of surgical skill.

IEEE transactions on neural systems and rehabilitation engineering : a publication of the IEEE Engineering in Medicine and Biology Society, Feb 16, 2017

The wide variation in upper extremity motor impairments among stroke survivors necessitates more ... more The wide variation in upper extremity motor impairments among stroke survivors necessitates more intelligent methods of customized therapy. However, current strategies for characterizing individual motor impairments are limited by the use of traditional clinical assessments (e.g. Fugl-Meyer) and simple engineering metrics (e.g. goal-directed performance). Our overall approach is to statistically identify the range of volitional movement capabilities, and then apply a robot-applied force vector field intervention that encourages under-expressed movements. We investigated whether explorative training with such customized force fields would improve stroke survivors' (n = 11) movement patterns in comparison to a control group that trained without forces (n = 11). Force and Control groups increased Fugl-Meyer UE scores (average of 1.0 and 1.1, respectively), which is not considered clinically meaningful. Interestingly, participants from both groups demonstrated dramatic increases in ...

Journal of NeuroEngineering and Rehabilitation, 2016

Background: While clinical assessments provide tools for characterizing abilities in motor-impair... more Background: While clinical assessments provide tools for characterizing abilities in motor-impaired individuals, concerns remain over their repeatability and reliability. Typical robot-assisted training studies focus on repetition of prescribed actions, yet such movement data provides an incomplete account of abnormal patterns of coordination. Recent studies have shown positive effects from self-directed movement, yet such a training paradigm leads to challenges in how to quantify and interpret performance. Methods: With data from chronic stroke survivors (n = 10, practicing for 3 days), we tabulated histograms of the displacement, velocity, and acceleration for planar motion, and examined whether modeling of distributions could reveal changes in available movement patterns. We contrasted these results with scalar measures of the range of motion. We performed linear discriminant analysis (LDA) classification with selected histogram features to compare predictions versus actual subject identifiers. As a basis of comparison, we also present an age-matched control group of healthy individuals (n = 10, practicing for 1 day). Results: Analysis of range of motion did not show improvement from self-directed movement training for the stroke survivors in this study. However, examination of distributions indicated that increased multivariate normal components were needed to accurately model the patterns of movement after training. Stroke survivors generally exhibited more complex distributions of motor exploration compared to the age-matched control group. Classification using linear discriminant analysis revealed that movement patterns were identifiable by individual. Individuals in the control group were more difficult to identify using classification methods, consistent with the idea that motor deficits contribute significantly to unique movement signatures. Conclusions: Distribution analysis revealed individual patterns of abnormal coordination in stroke survivors and changes in these patterns with training. These findings were not apparent from scalar metrics that simply summarized properties of motor exploration. Our results suggest new methods for characterizing motor capabilities, and could provide the basis for powerful tools for designing customized therapy.

Conference proceedings : ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Annual Conference, 2014

Manipulation of error feedback has been of great interest to recent studies in motor control and ... more Manipulation of error feedback has been of great interest to recent studies in motor control and rehabilitation. Typically, motor adaptation is shown as a change in performance with a single scalar metric for each trial, yet such an approach might overlook details about how error evolves through the movement. We believe that statistical distributions of movement error through the extent of the trajectory can reveal unique patterns of adaption and possibly reveal clues to how the motor system processes information about error. This paper describes different possible ordinate domains, focusing on representations in time and state-space, used to quantify reaching errors. We hypothesized that the domain with the lowest amount of variability would lead to a predictive model of reaching error with the highest accuracy. Here we showed that errors represented in a time domain demonstrate the least variance and allow for the highest predictive model of reaching errors. These predictive model...

2014 36th Annual International Conference of the IEEE Engineering in Medicine and Biology Society, 2014

Human movement ability should be described not only by its typical behavior, but also by the wide... more Human movement ability should be described not only by its typical behavior, but also by the wide variation in capabilities. This would mean that subjects that are encouraged to move throughout their workspace but otherwise free to move any way they like might reveal their unique movement tendencies. In this study, we investigate how much information (data) is needed to reliably construct a movement distribution that predicts an individual&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;s movement tendencies. We analyzed the distributions of position, velocity and acceleration data derived during self-directed motor exploration by stroke survivors (n=10 from a previous study) and healthy individuals (n=5). We examined whether these simple kinematic variables differed in terms of the amount of data required. We found a trend of decreasing time needed for characterization with the order of kinematic variable, for position, velocity, and acceleration, respectively. In addition, we investigated whether data requirements differ between stroke survivors and healthy. Our results suggest that healthy individuals may require more data samples (time for characterization), though the trend was only significant for position data. Our results provide an important step towards using statistical distributions to describe movement tendencies. Our findings could serve as more comprehensive tools to track recovery in or design more focused training intervention in neurorehabiliation applications.

2013 IEEE 13th International Conference on Rehabilitation Robotics (ICORR), 2013

Recent studies in rehabilitation have shown potential benefits of patient-initiated exploratory p... more Recent studies in rehabilitation have shown potential benefits of patient-initiated exploratory practice. Such findings, however, lead to new challenges in how to quantify and interpret movement patterns. We posit that changes in coordination are most evident in statistical distributions of movements. In a test on 10 chronic stroke subjects practicing for 3 days, we found that inter-quartile range of motion did not show improvement. However, a multivariate Gaussians analysis required more complexity at the end of training. Beyond simply characterizing movement, linear discriminant classification of each patient's movement distribution also identified that each patient's motor deficit left a unique signature. The greatest distinctions were observed in the space of accelerations (rather than position or velocity). These results suggest that unique deficits are best detected with such a distribution analysis, and also point to the need for customized interventions that consider such patient-specific motor deficits.

Neurorehabilitation Technology, 2011

Brain injury often results a partial loss of the neural resources communicating to the periphery ... more Brain injury often results a partial loss of the neural resources communicating to the periphery that controls movements. Consequently, the prior signals may no longer be appropriate for getting the muscles to do what is neededa new pattern needs to be learned that appropriately uses the residual resources. Such learning may not be too different from the learning of skills in sports, music performance, surgery, teleoperation, piloting, and child development. Our lab has leveraged what we know about neural adaptation and engineering control theory to develop and test new interactive environments that enhance learning (or relearning). One successful application is the use of robotics and video feedback technology to augment error signals, which tests standing hypotheses about error-mediated neuroplasticity and illustrates an exciting prospect for rehabilitation environments of tomorrow.

We conducted two experiments to determine what sensory feedback is required in a motor task where... more We conducted two experiments to determine what sensory feedback is required in a motor task where subjects manually excite oscillations of a virtual spring and inertia object. We examined performance considering the frequency content of the manual input, the consistency of phasing behavior between input and output motion, and the effective work rate by human subjects on the spring-inertia system. In Experiment-1, subjects (n=11) performed the manipulation task at a fixed resonant frequency (ωr=7 rad/s) with and without augmented sensory information, using only haptic feedback as the candidate channel. Including feedback resulted in superior performance in each metric (paired t-tests: p<.05). In Experiment-2, subjects (n=10) performed a similar task, with the additional challenge that various resonant frequencies were presented without preview (ωr= 7, 9, 11, 13 rad/s) under three feedback conditions: vision, haptic, or vision and haptic combined. Combined feedback demonstrated superior performance according to phase marker variability and effective work rate (paired t-tests: p<.05) in one case for ωr=7 rad/s. Our results demonstrate that a feedforward strategy is insufficient for maintaining resonant behavior of a spring-inertia system, while sensory feedback from vision or haptic sources allows the necessary on-line corrections and even rapid tuning to changes in the resonant frequency to occur.

We tested whether humans can learn to sense and compensate for interaction forces in contact task... more We tested whether humans can learn to sense and compensate for interaction forces in contact tasks. Many tasks, such as use of hand tools, involve significant interaction forces between hand and environment. One control strategy would be to use high hand impedance to reduce sensitivity to these forces. But an alternative would be to learn feedback compensation for the extrinsic dynamics and associated interaction forces, with the potential for lower control effort. We observed subjects as they learned control of a ball-and-beam system, a visuo-motor task where the goal was to quickly position a ball rolling atop a rotating beam, through manual rotation of the beam alone. We devised a ball-and-beam apparatus that could be operated in a real mode, where a physical ball was present; or in a virtual training mode, where the ball's dynamics were simulated in real time. The apparatus presented the same visual feedback in all cases, and optionally produced haptic feedback of the interaction forces associated with the ball's motion. Two healthy adult subject groups, Vision-Only and Vision-Haptics (each N=10), both trained for 80 trials on the simulated system, and then were evaluated on the real system to test for skill transfer effects. If humans incorporate interaction forces in their learning, the Vision-Haptics group would be expected to exhibit a smoother transfer, as quantified by changes in completion time of a ball-positioning task. During training, both groups adapted well to the task, with reductions of 64-70% in completion time. At skill transfer to the real system, the Vision-Only group had a significant 35% increase in completion time (p < 0.05). There was no significant change in the Vision-Haptics group, indicating that subjects had learned to compensate for interaction forces. These forces could potentially be incorporated in virtual environments to assist with motor training or rehabilitation.

IEEE Transactions on Haptics, 2012

To better understand how kinematic variables impact learning in surgical training, we devised an ... more To better understand how kinematic variables impact learning in surgical training, we devised an interactive environment for simulated laparoscopic maneuvers, using either 1) mechanical constraints typical of a surgical "box-trainer" or 2) virtual constraints in which free hand movements control virtual tool motion. During training, the virtual tool responded to the absolute position in space (Position-Based) or the orientation (Orientation-Based) of a hand-held sensor. Volunteers were further assigned to different sequences of target distances (Near-Far-Near or Far-Near-Far). Training with the Orientation-Based constraint enabled much lower path error and shorter movement times during training, which suggests that tool motion that simply mirrors joint motion is easier to learn. When evaluated in physically constrained (physical box-trainer) conditions, each group exhibited improved performance from training. However, Position-Based training enabled greater reductions in movement error relative to Orientation-Based (mean difference: 14.0 percent; CI: 0.7, 28.6). Furthermore, the Near-Far-Near schedule allowed a greater decrease in task time relative to the Far-Near-Far sequence (mean −13:5 percent, CI: −19:5, −7:5). Training that focused on shallow tool insertion (near targets) might promote more efficient movement strategies by emphasizing the curvature of tool motion. In addition, our findings suggest that an understanding of absolute tool position is critical to coping with mechanical interactions between the tool and trocar.

Experimental Brain Research, 2014

Several studies have suggested that the motor system takes advantage of a coordinate system when ... more Several studies have suggested that the motor system takes advantage of a coordinate system when learning a novel sensorimotor environment. Such investigations, however, have not distinguished between initial preferences of a coordinate system versus possible changes due to learning. Here, we present experimental methods that specifically entertain the possibility of multiple coordinate systems during generalization. Subjects trained with their right arm on a viscous force field. We evaluated their performances for both arms in an untrained workspace before and after training using three fields, each representing extrapolation with a candidate coordinate system. Surprisingly, our results showed evidence of improvement (pre to post) in all fields for both limbs. These findings are consistent with the hypothesis of multiple, simultaneous coordinate systems involved in generalization. We also investigated how feedback might affect the results and found in several cases that performance was better for visual displays that were aligned with the limb (in first person) versus non-aligned.

Journal of Neurophysiology, 2010

Recent human-machine interaction studies have suggested that movement augmented with negative vis... more Recent human-machine interaction studies have suggested that movement augmented with negative viscosity can enhance performance and can even promote better motor learning. To test this, we investigated how negative viscosity influences motor adaptation to an environment where forces acted only in one axis of motion. Using a force-feedback device, subjects performed free exploratory movements with a purely inertia generating forces proportional to hand acceleration, negative viscosity generating destabilizing forces proportional to hand velocity, or a combination of the acceleration and velocity fields. After training, we evaluated each subject's ability to perform circular movements in only the inertial field. Combined training resulted in lowest error and revealed similar responses as inertia training in catch trials. These findings are remarkable because negative viscosity, available only during training, evidently enhanced learning when combined with inertia. This success in ...

IEEE Transactions on Biomedical Engineering, 2013

With chronic stroke survivors (n = 30), we investigated how upper extremity training with negativ... more With chronic stroke survivors (n = 30), we investigated how upper extremity training with negative viscosity affects coordination under unperturbed conditions. Subjects trained with a planar robotic interface simulating 1) negative viscosity augmented to elbow and shoulder joints; 2) negative viscosity combined with inertia; or 3) a null-field condition. Two treatment groups practiced with both force conditions (cross-over design), while a control group practiced with a null-field condition. Training (exploratory movement) and evaluations (prescribed circular movement) alternated in several phases to facilitate transfer from forces to the null field. Negative viscosity expanded exploration especially in the sagittal axis, and resulted in significant within-day improvements. Both treatment groups exhibited next day retention unobserved in the control. Our results suggest enhanced learning from forces that induce a broader range of kinematics. This study supports the use of robot-assisted training that encourages active patient involvement by preserving efferent commands for driving movement.

We devised an interactive environment in which subjects could perform simulated laparoscopic mane... more We devised an interactive environment in which subjects could perform simulated laparoscopic maneuvers, using either unconstrained movements or standard mechanical contact typical of a box-trainer. During training the virtual tool responded to the absolute position in space (Position-Based) or the orientation (Orientation-Based) of a hand-held sensor. Volunteers were further assigned to different sequences of target distances (Near-Far-Near or Far-Near-Far). Orientation-Based control produced much lower error and task times during training, which suggests that the motor system more easily accommodates tool use with degrees of freedom that match joint angles. When evaluated in constrained (physical box-trainer) conditions, each group exhibited improved performance from training. However, Position-Based training enabled greater reductions in movement error relative to Orientation-Based (mean −13.7%, CI:−27.1, −0.4). Furthermore, the Near-Far-Near schedule allowed a greater decrease in task time relative to the Far-Near-Far sequence (mean −13.5%, CI:−19.5, −7.5). Training at shallow insertion in virtual laparoscopy might promote more efficient movement strategies by emphasizing the curvature of tool motion. In addition, our findings suggest that an understanding of absolute tool position is critical to coping with mechanical interactions between the tool and trochar.

Because recent preliminary evidence points to the use of Error augmentation (EA) for motor learni... more Because recent preliminary evidence points to the use of Error augmentation (EA) for motor learning enhancements, we visually enhanced deviations from a straight line path while subjects practiced a sensorimotor reversal task, similar to laparoscopic surgery. Our study asked 10 healthy subjects in two groups to perform targeted reaching in a simulated virtual reality environment, where the transformation of the hand position matrix was a complete reversal-rotated 180 degrees about an arbitrary axis (hence 2 of the 3 coordinates are reversed). Our data showed that after 500 practice trials, error-augmented-trained subjects reached the desired targets more quickly and with lower error (differences of 0.4 seconds and 0.5 cm Maximum Perpendicular Trajectory deviation) when compared to the control group. Furthermore, the manner in which subjects practiced was influenced by the error augmentation, resulting in more continuous motions for this group and smaller errors. Even with the extreme sensory discordance of a reversal, these data further support that distorted reality can promote more complete adaptation/learning when compared to regular training. Lastly, upon removing the flip all subjects quickly returned to baseline rapidly within 6 trials.

With stroke survivors (n=30) as the test population, we investigated how upper extremity training... more With stroke survivors (n=30) as the test population, we investigated how upper extremity training with negative viscosity affects coordination in unassisted conditions. Using a planar force-feedback device, subjects performed exploratory movements within an environment that simulated 1) negative viscosity added to elbow and shoulder joints 2) augmented inertia to the upper and lower arm combined with negative viscosity, or 3) a null force field (control). After training, we evaluated each subject&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;s ability to perform circular movements in the null field. Negative viscosity training resulted in greater within-day reductions in error compared with the combined field training. Negative viscosity promoted greater distributions of accelerations during free exploration, especially in the sagittal axis, while combined field training diminished overall activity. Both force field training groups exhibited next day retention, while this was not observed for the control group. The improvement in performance suggests that greater range of kinematic experiences contribute to learning, even despite novel force field environments. These findings provide support for the use of movement amplifying environments for upper extremity rehabilitation, allowing greater access to training while maintaining user engagement.

We investigated how free interaction with an object influences the formation of motor planning. S... more We investigated how free interaction with an object influences the formation of motor planning. Subjects controlled a force-feedback planar manipulandum that presented simulated anisotropic inertial forces. As a performance evaluation, subjects made circular movements about a prescribed track. In order to investigate potential enhancement of motor planning, we introduced negative damping during an ldquointeractive primingrdquo phase prior to task performance. As a control, we presented a second subject group with normal interactive priming. Our results showed significantly greater reduction in maximum curvature error for the subject group that received enhanced priming (two-tailed T-test, p=1.86e-6) compared to the control group. Group-I demonstrated a 34.8% reduction in error while Group-II achieved 5.78% reduction. We also observed that the presentation of enhanced priming evidently caused a greater sensitivity to catch trials compared to the control. Group-I demonstrated a larger increase (92.0%) in maximum curvature error in catch- trials (with respect to baseline), compared to Group-II (50.8%) during early training (two-tailed T-test, p=1.9e-3). These results suggest that some forms of augmentation to task dynamics - leading to the exploration of a broader state space -can help the accelerate the learning of control strategies suitable for an unassisted environment. The finding is also consistent with the hypothesis that subjects can decompose the environment impedance into acceleration and velocity dependent elements.

We investigated how learning of inertial load manipulation is influenced by movement amplificatio... more We investigated how learning of inertial load manipulation is influenced by movement amplification with negative viscosity. Using a force-feedback device, subjects trained on anisotropic loads (5 orientations) with free movements in one of three conditions (inertia only, negative viscosity only, or combined), prior to common evaluation conditions (prescribed circular pattern with inertia only). Training with combined-load resulted in lower error (6.89 plusmn 3.25%) compared to inertia-only (8.40 plusmn 4.32%) and viscosity-only (8.17 plusmn 4.13%) according to radial deviation analysis (% of trial mean radius). Combined-Load and inertia-only groups exhibited similar unexpected no-load trials (8.38 plusmn 4.31% versus 8.91 plusmn 4.70% of trial mean radius), which suggests comparable low-impedance strategies. These findings are remarkable since negative viscosity, only available during training, evidently enhanced learning when combined with inertia. Modeling analysis suggests that a feedforward after-effect of negative viscosity cannot predict such performance gains. Instead, results from combined-load training are consistent with greater feedforward inertia compensation along with a small increase in impedance control. The capability of the nervous system to generalize learning from negative viscosity suggests an intriguing new method for enhancing sensorimotor adaptation.