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Poster Abstract Book ABSTRACT BOOK NCM VIRTUAL 30th Annual Meeting April 20 – 22, 2021 photo © Juan Carlos Fonseca Mata #NCM2021 www.ncm-society.org Table of Contents Poster Session 1 ............................................................................................................................................ 2 A – Control of Eye & Head Movement ...................................................................................................... 2 B – Fundamentals of Motor Control ......................................................................................................... 4 C – Posture and Gait ............................................................................................................................... 16 D – Integrative Control of Movement ..................................................................................................... 25 E – Disorders of Motor Control ............................................................................................................... 32 F – Adaptation & Plasticity in Motor Control .......................................................................................... 38 G – Theoretical & Computational Motor Control ................................................................................... 54 Poster Session 2 .......................................................................................................................................... 61 A – Control of Eye and Head Movement ................................................................................................ 61 B – Fundamentals of Motor Control ....................................................................................................... 63 C – Posture and Gait ............................................................................................................................... 74 D – Integrative Control of Movement ..................................................................................................... 82 E – Disorders of Motor Control ............................................................................................................... 89 F – Adaptation & Plasticity in Motor Control .......................................................................................... 95 G – Theoretical & Computational Motor Control ................................................................................. 110 Poster Session 3 ........................................................................................................................................ 119 A – Control of Eye and Head Movement .............................................................................................. 119 B – Fundamentals of Motor Control ..................................................................................................... 121 C – Posture and Gait ............................................................................................................................. 133 D – Integrative Control of Movement ................................................................................................... 141 E – Disorders of Motor Control ............................................................................................................. 148 F – Adaptation & Plasticity in Motor Control ........................................................................................ 154 G – Theoretical & Computational Motor Control ................................................................................. 169 NCM 2021 Poster Abstracts Poster Session 1 A – Control of Eye & Head Movement 1-A-1 Gain adaptation and variability of vestibular corticothalamic neurons shape our perception of natural self motion stimuli Presenting Author: Jerome Carriot Authors: Jerome Carriot¹, Isabelle Mackrous¹, Graham McAllister¹, Hamed Hooshangnejad², Kathleen Cullen², Chacron Maurice¹ ¹McGill University, ²Johns Hopkins University Natural stimuli display complex spatiotemporal characteristics that vary over many orders of magnitude. In order to encode such stimuli efficiently, sensory systems must continuously adapt by changing their response properties. However, the computational role of such adaptation remains poorly understood in the context in which adaptation can increase coding ambiguity. Here we first investigated how vestibular thalamocortical neurons and their afferent input neurons within the vestibular nuclei respond to both simple artificial and more complex natural self-motion stimuli in rhesus macaques. We found that both groups displayed comparable response properties to artificial stimuli which led to ambiguity. However, while such ambiguity persisted for artificial stimuli for vestibular nuclei neurons, vestibular thalamocortical neurons instead faithfully and unambiguously followed the detailed timecourse of natural self-motion stimuli. A mathematical model including known filtering properties as well as gain adaptation successfully reproduced our experimental data, thereby showing that gain adaptation plays an essential role towards removing coding ambiguity. We demonstrate that vestibular thalamocortical neurons are best optimized to encode natural self-motion stimuli as opposed to vestibular nuclei neurons. Our results challenge the common wisdom that adaptation leads to ambiguity by showing that, instead, such adaptation actually leads to faithful and unambiguous encoding of natural stimuli. Second, we investigated the role of these vestibular thalamocortical neurons in the perception of self-motion. Specifically, we tested whether their responses can account for a violation of Weber's law, namely that discrimination performance is enhanced at higher stimulus amplitudes. To do so, we quantified how neuronal gain and variability varied as a function of stimulus amplitude and computed neural discrimination thresholds. While neural gain strongly decreased as a function of stimulus amplitude, neural variability instead initially increased at low values but saturated at high values. As a result, neural thresholds were not proportional to stimulus amplitude as they also saturated at higher values. Further, while single neuron discrimination thresholds were two-fold higher than those of perception, values computed from neural populations agreed with perception for all amplitudes. Thus, overall, the dependency of neural population discrimination thresholds on stimulus amplitude can explain why vestibular perceptual performance is better than that predicted from Weber's law. Our results uncover a novel role for neural variability in shaping how sensory pathways generate perception. Taken together, we further provide novel insights as to how variability and gain control contribute to adaptive encoding of natural stimuli with continually varying statistics. 1-A-2 The effect of spatial frequency on visual-vestibular conflict detection and self-reported simulator sickness Presenting Author: Savannah Halow Authors: Savannah Halow¹, Paul MacNeilage¹, Eelke Folmer¹ ¹University of Nevada, Reno Perception of a stable visual environment depends on mechanisms that monitor the agreement between visual and non-visual cues to head movement. Visual cues include a combination of optic flow and oculomotor signals needed to bring retinal motion into head coordinates. Non-visual cues include vestibular signals as well as efference copies of motor commands to rotate the head on the body. Conflict between these signals is associated with debilitating conditions such as motion or simulator sickness. Here we investigate how characteristics of the visual scene impact observers' ability to detect visual-vestibular conflict and the corresponding levels of subjective simulator sickness. Experiments were conducted using a head-mounted display (HTC Vive Pro Eye) with fixation behavior monitored by its embedded eye tracker. On each trial, participants made active yaw head movements of ~30 deg over 1.5 sec while fixating a scene- or head-fixed point. During the head movement, the gain on the visual scene motion was manipulated. Participants were asked to report whether the gain was too low or too high, that is, if the environment appeared to be moving with or against head movement, respectively. Additionally, participants were asked to report their relative level of sickness approximately every 3 minutes during the experiment based on a 1-10 Discomfort Score scale. Finally, participants also filled out a Simulator Sickness Questionnaire immediately after each of the condition blocks. Fitting a psychometric function to the resulting data yields the gain perceived as stationary (PSE) and the range of gains that are compatible with perception of a stationary visual environment (JND), referred to by Wallach as the Range of Immobility. Participants were tested using a virtually rendered optokinetic drum with either a low or high-frequency stripe pattern. Our results revealed higher visual gains were seen as stationary (lower PSEs) in the low-frequency condition suggesting slower perceived speed of scene motion. This is consistent with the known effect of spatial frequency on perceived speed of retinal image motion. Sensitivity to conflict was also best (lower JND) in the low-frequency condition consistent with the idea of signal-dependent noise on estimated scene motion. These results quantify the relationship between spatial frequency, detection of visual-vestibular conflict, and self-reported simulator sickness. Acknowledgments: Research was supported
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