Biology subjects

Seel, T.

Publications and source records attributed to Seel, T..

2 recordsLinked to original sources

bioRxiv2023

Comparing sparse inertial sensor setups for sagittal-plane walking and running reconstructions

Estimating spatiotemporal, kinematic, and kinetic movement variables with little obtrusion to the user is critical for clinical and sports applications. Previously, we developed an approach to estimate these variables from measurements with seven lower-body inertial sensors, i.e., the full setup, using optimal control simulations. Here, we investigated if this approach is similarly accurate when using sparse sensor setups with less inertial sensors. To estimate the movement variables, we solved optimal control problems on sagittal plane lower-body musculoskeletal models, in which an objective was optimized that combined tracking of accelerometer and gyroscope data with minimizing muscular effort. We created simulations for 10 participants at three walking and three running speeds, using seven sensor setups with between two and seven sensors located at the feet, shank, thighs, and/or pelvis. We calculated the correlation and root mean square deviations (RMSDs) between the estimated movement variables and those from inverse analysis using optical motion capture (OMC) and force plate data. We found that correlations between IMU- and OMC-based variables were high for all sensor setups, while including all sensors did not necessarily lead to the smallest RMSDs. Setups without a pelvis sensor led to too much forward trunk lean and inaccurate spatiotemporal variables. RMSDs were highest for the setup with two foot-worn IMUs. The smallest setup that estimated joint angles as accurately as the full setup (<1 degree difference in RMSD) was the setup with IMUs at the feet and thighs. The mean correlations for joint angles, moments, and ground reaction forces were at least 0.8 for walking and 0.9 for running when either a pelvic sensor or thigh sensors were included. Therefore, we conclude that we can accurately perform a comprehensive sagittal-plane motion analysis with sparse sensor setups when sensors are placed on the feet and on either the pelvis or the thighs.

bioengineering↗

bioRxiv2023

Saccadic omission revisited: What saccade-induced smear looks like

During active visual exploration, saccadic eye movements rapidly shift the visual image across the human retina. Although these high-speed shifts occur at a high rate and introduce considerable amounts of motion smear during natural vision, our perceptual experience is oblivious to it. This saccadic omission, however, does not entail that saccadeinduced motion smear cannot be perceived in principle. Using tachistoscopic displays of natural scenes, we rendered saccade-induced smear highly conspicuous. By systematically manipulating peri-saccadic display durations we studied the dynamics of smear in a time-resolved manner, assessing identification performance of smeared scenes, as well as perceived smear amount and direction. Both measures showed distinctive, U-shaped time courses throughout the saccade, indicating that generation and reduction of perceived smear occurred during saccades. Moreover, low spatial frequencies and orientations parallel to the direction of the ongoing saccade were identified as the predominant visual features encoded in motion smear. We explain these findings using computational models that assume no more than saccadic velocity and human contrast sensitivity profiles, and present a motion-filter model capable of predicting observers perceived amount of smear based on their eyes trajectories, suggesting a direct link between perceptual and saccade dynamics. Replays of the visual consequences of saccades during fixation led to virtually identical results as actively making saccades, whereas the additional simulation of perisaccadic contrast suppression heavily reduced this similarity, providing strong evidence that no extra-retinal process was needed to explain our results. Saccadic omission of motion smear may be conceptualized as a parsimonious visual mechanism that emerges naturally from the interplay of retinal consequences of saccades and early visual processing.

neuroscience↗