Postural stability assessment in expert versus amateur basketball players during optic flow stimulation.

We evaluated the role of visual stimulation on postural muscles and the changes in the center of pressure (CoP) during standing posture in expert and amateur basketball players. Participants were instructed to look at a fixation point presented on a screen during foveal, peripheral, and full field optic flow stimuli. Postural mechanisms and motor strategies were assessed by simultaneous recordings of stabilometric, oculomotor, and electromyographic data during visual stimulation. We found significant differences between experts and amateurs in the orientation of visual attention. Experts oriented attention to the right of their visual field, while amateurs to the bottom-right. The displacement in the CoP mediolateral direction showed that experts had a greater postural sway of the right leg, while amateurs on the left leg. The entropy-based data analysis of the CoP mediolateral direction exhibited a greater value in amateurs than in experts. The root-mean-square and the coactivation index analysis showed that experts activated mainly the right leg while amateurs the left leg. In conclusion, playing sports for years seems to have induced some strong differences in the standing posture between the right and left sides. Even during non-ecological visual stimulation, athletes maintain postural adaptations to counteract the body oscillation.

A mental workload and biomechanical assessment during split-belt locomotor adaptation with and without optic flow.

Adaptive human performance relies on the central nervous system to regulate the engagement of cognitive-motor resources as task demands vary. Despite numerous studies which employed a split-belt induced perturbation to examine biomechanical outcomes during locomotor adaptation, none concurrently examined the cerebral cortical dynamics to assess changes in mental workload. Additionally, while prior work suggests that optic flow provides critical information for walking regulation, a few studies have manipulated visual inputs during adaption to split-belt walking. This study aimed to examine the concurrent modulation of gait and Electroencephalography (EEG) cortical dynamics underlying mental workload during split-belt locomotor adaptation, with and without optic flow. Thirteen uninjured participants with minimal inherent walking asymmetries at baseline underwent adaptation, while temporal-spatial gait and EEG spectral metrics were recorded. The results revealed a reduction in step length and time asymmetry from early to late adaptation, accompanied by an elevated frontal and temporal theta power; the former being well corelated to biomechanical changes. While the absence of optic flow during adaptation did not affect temporal-spatial gait metrics, it led to an increase of theta and low-alpha power. Thus, as individuals adapt their locomotor patterns, the cognitive-motor resources underlying the encoding and consolidation processes of the procedural memory were recruited to acquire a new internal model of the perturbation. Also, when adaption occurs without optic flow, a further reduction of arousal is accompanied with an elevation of attentional engagement due to enhanced neurocognitive resources likely to maintain adaptive walking patterns.

Structurally-constrained optical-flow-guided adversarial generation of synthetic CT for MR-only radiotherapy treatment planning.

The rapid progress in image-to-image translation methods using deep neural networks has led to advancements in the generation of synthetic CT (sCT) in MR-only radiotherapy workflow. Replacement of CT with MR reduces unnecessary radiation exposure, financial cost and enables more accurate delineation of organs at risk. Previous generative adversarial networks (GANs) have been oriented towards MR to sCT generation. In this work, we have implemented multiple augmented cycle consistent GANs. The augmentation involves structural information constraint (StructCGAN), optical flow consistency constraint (FlowCGAN) and the combination of both the conditions (SFCGAN). The networks were trained and tested on a publicly available Gold Atlas project dataset, consisting of T2-weighted MR and CT volumes of 19 subjects from 3 different sites. The network was tested on 8 volumes acquired from the third site with a different scanner to assess the generalizability of the network on multicenter data. The results indicate that all the networks are robust to scanner variations. The best model, SFCGAN achieved an average ME of 0.9   5.9 HU, an average MAE of 40.4   4.7 HU and 57.2   1.4 dB PSNR outperforming previous research works. Moreover, the optical flow constraint between consecutive frames preserves the consistency across all views compared to 2D image-to-image translation methods. SFCGAN exploits the features of both StructCGAN and FlowCGAN by delivering structurally robust and 3D consistent sCT images. The research work serves as a benchmark for further research in MR-only radiotherapy.

Preliminary Assessment of an Optical Flow Method (OFM) for Nonrigid Registration and Temporal Subtraction (TS) of Serial CT Examinations to Facilitate Evaluation of Interval Change in Metastatic Lung Nodules.

RATIONALE AND OBJECTIVES: Accurate assessment of size change of lung nodules on chest computed tomography (CT) is important for diagnosis and response assessment. However, manual methods are time-consuming and error-prone. We therefore assessed whether an optical flow method (OFM) with temporal subtraction (TS) can facilitate detection and quantification of lung nodule change on serial CT datasets. MATERIALS AND METHODS: Serial chest CT examinations were selected from 12 patients with multiple pulmonary metastases. Lung nodules were evaluated for change in size using: (1) OFM with TS and (2) reference standard visual and manual assessment. Average time required to assess interval change using both methods was recorded and compared. Concordance of agreement between OFM with TS and reference standard assessment for nodule change was examined. RESULTS: 285 solid pulmonary nodules were evaluated. The average time per nodule to assess interval change in nodule size by OFM with TS (mean 1.15 + 0.5 minutes) was significantly less (P = 0.02) than that the reference standard approach (mean 1.56 + 0.5 minutes). Agreement between OFM with TS and reference standard occurred for 63.2% of nodules overall (kappa = 0.50, standard error 0.35, P< 0.00001), and significantly increased with larger nodule size (kappa = 0.48 for nodules <5 mm; kappa = 0.94 for nodules >20 mm, P < 0.0001). CONCLUSIONS: This preliminary study demonstrates the feasibility of an OFM with TS to assess for interval change in metastatic lung nodules on serial CT examinations with significantly improved reading speed and moderate agreement relative to reference standard assessment. Agreement improved with larger nodule size.

Visual Breast Asymmetry Assessment with Optical-Flow Algorithm.

Breast surgery is one of the most important procedures in cosmetic and reconstructive surgery. However, there is no ideal method to assess results. One of the greatest difficulties is the subjective aspect of evaluation. In recent years, several objective computer systems have been proposed and validated as assessment methods, such as BCCT®, OBCS®, GBAI©, etc. In this study, we propose a novel system named VIBA©, that uses an Optical Flow (OF) algorithm which objectively classifies results into symmetrical and asymmetrical categories, with a numerical score. Software was developed in MATLAB (MATLAB and Statistics Toolbox Release 2018b, The MathWorks, Inc., Natick, Massachusetts, USA) called VIBA-Calc© (VIBA stands for VIsual Breast Asymmetry). We compared our OF score with the well-established asymmetry scoring system called Objective Breast Cosmesis Scale (OBCS®). In order to do so, we studied 100 frontal photographs of patients who underwent aesthetic breast surgery between 2017 and 2018, from the senior author's private practice. VIBA-Calc© allows the user to load an image and then draw a rectangle containing both breasts. By simply clicking on a button, the program finds the midline of the rectangle and calculates the final score, as well as the color map of asymmetric regions. Classification into symmetric or asymmetric categories using OBCS and VIBA scores agreed in most cases. Concordance between both classification systems was almost perfect in the group of postoperative cases (k = 0.84; p < 0.001), and substantial in preoperative cases (k = 0.76; p < 0.001). Global Cohen's kappa coefficient was 0.80 (p < 0.001). VIBA© is a useful tool for pre- and post-operative evaluation of breasts, that could be used both in reconstructive and aesthetic surgery.

The stereoscopic advantage for vection persists despite reversed disparity.

Research has shown that consistent stereoscopic information improves the vection (i.e. illusions of self-motion) induced in stationary observers. This study investigates the effects of placing stereoscopic information into direct conflict with monocular motion signals by swapping the observer's left and right eye views to reverse disparity. Experiments compared the vection induced by stereo-consistent, stereo-reversed and flat-stereo patterns of: (1) same-size optic flow, which contained monocular motion perspective information about self-motion, and (2) changing-size optic flow, which provided additional monocular information about motion-in-depth based on local changes in object image sizes. As expected, consistent stereoscopic information improved the vection-in-depth induced by both changing-size and same-size patterns of optic flow. Unexpectedly, stereo-reversed patterns of same-size optic flow also induced stronger vection-in-depth than flat-stereo patterns of same-size optic flow. The effects of stereo-consistent and stereo-reversed information on vection strength were found to correlate reliably with their effects on perceived motion-in-depth and motion after-effect durations, but not with their effects on perceived scene depth. This suggests that stereo-consistent and stereo-reversed advantages for vection were both due to effects on perceived motion-in-depth. The current findings clearly demonstrate that stereoscopic information does not need to be consistent with monocular motion signals in order to improve vection. When taken together with past findings, they suggest that stereoscopic information only needs to be dynamic (as opposed to static) in order to improve vection-in-depth.

Bio-inspired modeling and implementation of the ocelli visual system of flying insects.

Two visual sensing modalities in insects, the ocelli and compound eyes, provide signals used for flight stabilization and navigation. In this article, a generalized model of the ocellar visual system is developed for a 3-D visual simulation environment based on behavioral, anatomical, and electrophysiological data from several species. A linear measurement model is estimated from Monte Carlo simulation in a cluttered urban environment relating state changes of the vehicle to the outputs of the ocellar model. A fully analog-printed circuit board sensor based on this model is designed and fabricated. Open-loop characterization of the sensor to visual stimuli induced by self motion is performed. Closed-loop stabilizing feedback of the sensor in combination with optic flow sensors is implemented onboard a quadrotor micro-air vehicle and its impulse response is characterized.