Enhanced cognitive interference during visuomotor tasks may cause eye-hand dyscoordination.

In complex visuomotor tasks, such as cooking, people make many saccades to continuously search for items before and during reaching movements. These tasks require cognitive resources, such as short-term memory and task-switching. Cognitive load may impact limb motor performance by increasing demands on mental processes, but mechanisms remain unclear. The Trail-Making Tests, in which participants sequentially search for and make reaching movements to 25 targets, consist of a simple numeric variant (Trails-A) and a cognitively challenging variant that requires alphanumeric switching (Trails-B). We have previously shown that stroke survivors and age-matched controls make many more saccades in Trails-B, and those increases in saccades are associated with decreases in speed and smoothness of reaching movements. However, it remains unclear how patients with neurological injuries, e.g., stroke, manage progressive increases in cognitive load during visuomotor tasks, such as the Trail-Making Tests. As Trails-B trial progresses, switching between numbers and letters leads to progressive increases in cognitive load. Here, we show that stroke survivors with damage to frontoparietal areas and age-matched controls made more saccades and had longer fixations as they progressed through the 25 alphanumeric targets in Trails-B. Furthermore, when stroke survivors made saccades during reaching movements in Trails-B, their movement speed slowed down significantly. Thus, damage to frontoparietal areas serving cognitive motor functions may cause interference between oculomotor, visual, and limb motor functions, which could lead to significant disruptions in activities of daily living. These findings augment our understanding of the mechanisms that underpin cognitive-motor interference during complex visuomotor tasks.

UNav: An Infrastructure-Independent Vision-Based Navigation System for People with Blindness and Low Vision.

Vision-based localization approaches now underpin newly emerging navigation pipelines for myriad use cases, from robotics to assistive technologies. Compared to sensor-based solutions, vision-based localization does not require pre-installed sensor infrastructure, which is costly, time-consuming, and/or often infeasible at scale. Herein, we propose a novel vision-based localization pipeline for a specific use case: navigation support for end users with blindness and low vision. Given a query image taken by an end user on a mobile application, the pipeline leverages a visual place recognition (VPR) algorithm to find similar images in a reference image database of the target space. The geolocations of these similar images are utilized in a downstream task that employs a weighted-average method to estimate the end user's location. Another downstream task utilizes the perspective-n-point (PnP) algorithm to estimate the end user's direction by exploiting the 2D-3D point correspondences between the query image and the 3D environment, as extracted from matched images in the database. Additionally, this system implements Dijkstra's algorithm to calculate a shortest path based on a navigable map that includes the trip origin and destination. The topometric map used for localization and navigation is built using a customized graphical user interface that projects a 3D reconstructed sparse map, built from a sequence of images, to the corresponding a priori 2D floor plan. Sequential images used for map construction can be collected in a pre-mapping step or scavenged through public databases/citizen science. The end-to-end system can be installed on any internet-accessible device with a camera that hosts a custom mobile application. For evaluation purposes, mapping and localization were tested in a complex hospital environment. The evaluation results demonstrate that our system can achieve localization with an average error of less than 1 m without knowledge of the camera's intrinsic parameters, such as focal length.

Real-Time Loosely Coupled 3DMA GNSS/Doppler Measurements Integration Using a Graph Optimization and Its Performance Assessments in Urban Canyons of New York.

Smart health applications have received significant attention in recent years. Novel applications hold significant promise to overcome many of the inconveniences faced by persons with disabilities throughout daily living. For people with blindness and low vision (BLV), environmental perception is compromised, creating myriad difficulties. Precise localization is still a gap in the field and is critical to safe navigation. Conventional GNSS positioning cannot provide satisfactory performance in urban canyons. 3D mapping-aided (3DMA) GNSS may serve as an urban GNSS solution, since the availability of 3D city models has widely increased. As a result, this study developed a real-time 3DMA GNSS-positioning system based on state-of-the-art 3DMA GNSS algorithms. Shadow matching was integrated with likelihood-based ranging 3DMA GNSS, generating positioning hypothesis candidates. To increase robustness, the 3DMA GNSS solution was then optimized with Doppler measurements using factor graph optimization (FGO) in a loosely-coupled fashion. This study also evaluated positioning performance using an advanced wearable system's recorded data in New York City. The real-time forward-processed FGO can provide a root-mean-square error (RMSE) of about 21 m. The RMSE drops to 16 m when the data is post-processed with FGO in a combined direction. Overall results show that the proposed loosely-coupled 3DMA FGO algorithm can provide a better and more robust positioning performance for the multi-sensor integration approach used by this wearable for persons with BLV.

Dysfunctional mode switching between fixation and saccades: collaborative insights into two unusual clinical disorders.

Voluntary rapid eye movements (saccades) redirect the fovea toward objects of visual interest. The saccadic system can be considered as a dual-mode system: in one mode the eye is fixating, in the other it is making a saccade. In this review, we consider two examples of dysfunctional saccades, interrupted saccades in late-onset Tay-Sachs disease and gaze-position dependent opsoclonus after concussion, which fail to properly shift between fixation and saccade modes. Insights and benefits gained from bi-directional collaborative exchange between clinical and basic scientists are emphasized. In the case of interrupted saccades, existing mathematical models were sufficiently detailed to provide support for the cause of interrupted saccades. In the case of gaze-position dependent opsoclonus, existing models could not explain the behavior, but further development provided a reasonable hypothesis for the mechanism underlying the behavior. Collaboration between clinical and basic science is a rich source of progress for developing biologically plausible models and understanding neurological disease. Approaching a clinical problem with a specific hypothesis (model) in mind often prompts new experimental tests and provides insights into basic mechanisms.

How sandbag-able are concussion sideline assessments? A close look at eye movements to uncover strategies.

Background: Sideline diagnostic tests for concussion are vulnerable to volitional poor performance ("sandbagging") on baseline assessments, motivated by desire to subvert concussion detection and potential removal from play. We investigated eye movements during sandbagging versus best effort on the King-Devick (KD) test, a rapid automatized naming (RAN) task.Methods: Participants performed KD testing during oculography following instructions to sandbag or give best effort.Results: Twenty healthy participants without concussion history were included (mean age 27 ± 8 years). Sandbagging resulted in longer test times (89.6 ± 39.2 s vs 48.2 ± 8.5 s, p < .001), longer inter-saccadic intervals (459.5 ± 125.4 ms vs 311.2 ± 79.1 ms, p < .001) and greater numbers of saccades (171.4 ± 47 vs 138 ± 24.2, p < .001) and reverse saccades (wrong direction for reading) (21.2% vs 11.3%, p < .001). Sandbagging was detectable using a logistic model with KD times as the only predictor, though more robustly detectable using eye movement metrics.Conclusions: KD sandbagging results in eye movement differences that are detectable by eye movement recordings and suggest an invalid test score. Objective eye movement recording during the KD test shows promise for distinguishing between best effort and post-injury performance, as well as for identifying sandbagging red flags.

Detection of normal and slow saccades using implicit piecewise polynomial approximation.

The quantitative analysis of saccades in eye movement data unveils information associated with intention, cognition, and health status. Abnormally slow saccades are indicative of neurological disorders and often imply a specific pathological disturbance. However, conventional saccade detection algorithms are not designed to detect slow saccades, and are correspondingly unreliable when saccades are unusually slow. In this article, we propose an algorithm that is effective for the detection of both normal and slow saccades. The proposed algorithm is partly based on modeling saccadic waveforms as piecewise-quadratic signals. The algorithm first decreases noise in acquired eye-tracking data using optimization to minimize a prescribed objective function, then uses velocity thresholding to detect saccades. Using both simulated saccades and real saccades generated by healthy subjects and patients, we evaluate the performance of the proposed algorithm and 10 other detection algorithms. We show the proposed algorithm is more accurate in detecting both normal and slow saccades than other algorithms.

Eye Movement Recordings: Practical Applications in Neurology.

Accurate detection and interpretation of eye movement abnormalities often guides differential diagnosis, discussions on prognosis and disease mechanisms, and directed treatment of disabling visual symptoms and signs. A comprehensive clinical eye movement examination is high yield from a diagnostic standpoint; however, skillful recording and quantification of eye movements can increase detection of subclinical deficits, confirm clinical suspicions, guide therapeutics, and generate expansive research opportunities. This review encompasses an overview of the clinical eye movement examination, provides examples of practical diagnostic contributions from quantitative recordings of eye movements, and comments on recording equipment and related challenges.

History and Future Directions of Vision Testing in Head Trauma.

BACKGROUND: Concussion leads to neurophysiologic changes that may result in visual symptoms and changes in ocular motor function. Vision-based testing is used increasingly to improve detection and assess head injury. This review will focus on the historical aspects and emerging data for vision tests, emphasizing rapid automatized naming (RAN) tasks and objective recording techniques, including video-oculography (VOG), as applied to the evaluation of mild traumatic brain injury. METHODS: Searches on PubMed were performed using combinations of the following key words: "concussion," "mild traumatic brain injury," "rapid automatized naming," "King-Devick," "mobile universal lexicon evaluation system," "video-oculography," and "eye-tracking." Additional information was referenced from web sites of vendors of commercial eye-tracking systems and services. RESULTS: Tests of rapid number, picture, or symbol naming, termed RAN tasks, have been used in neuropsychological studies since the early 20th century. The visual system contains widely distributed networks that are readily assessed by a variety of functionally distinct RAN tasks. The King-Devick test, a rapid number naming assessment, and several picture-naming tests, such as the Mobile Universal Lexicon Evaluation System (MULES) and the modified Snodgrass and Vanderwart image set, show capacity to identify athletes with concussion. VOG has gained widespread use in eye- and gaze-tracking studies of head trauma from which objective data have shown increased saccadic latencies, saccadic dysmetria, errors in predictive target tracking, and changes in vergence in concussed subjects. Performance impairments on RAN tasks and on tasks recorded with VOG are likely related to ocular motor dysfunction and to changes in cognition, specifically to attention, memory, and executive functioning. As research studies on ocular motor function after concussion have expanded, so too have commercialized eye-tracking systems and assessments. However, these commercial services are still investigational and all vision-based markers of concussion require further validation. CONCLUSIONS: RAN tasks and VOG assessments provide objective measures of ocular motor function. Changes in ocular motor performance after concussion reflect generalized neurophysiologic changes affecting a variety of cognitive processes. Although these tests are increasingly used in head injury assessments, further study is needed to validate them as adjunctive diagnostic aids and assessments of recovery.

Evolution of Visual Outcomes in Clinical Trials for Multiple Sclerosis Disease-Modifying Therapies.

: BACKGROUND:: The visual pathways are increasingly recognized as an ideal model to study neurodegeneration in multiple sclerosis (MS). Low-contrast letter acuity (LCLA) and optical coherence tomography (OCT) are validated measures of function and structure in MS. In fact, LCLA was the topic of a recent review by the Multiple Sclerosis Outcome Assessments Consortium (MSOAC) to qualify this visual measure as a primary or secondary clinical trial endpoint with the Food and Drug Administration (FDA) and other regulatory agencies. This review focuses on the use of LCLA and OCT measures as outcomes in clinical trials to date of MS disease-modifying therapies. METHODS: A Pubmed search using the specific key words "optical coherence tomography," "low-contrast letter acuity," "multiple sclerosis," and "clinical trials" was performed. An additional search on the clinicaltrials.gov website with the same key words was used to find registered clinical trials of MS therapies that included these visual outcome measures. RESULTS: As demonstrated by multiple clinical trials, LCLA and OCT measures are sensitive to treatment effects in MS. LCLA has been used in many clinical trials to date, and findings suggest that 7 letters of LCLA at the 2.5% contrast level are meaningful change. Few clinical trials using the benefits of OCT have been performed, although results of observational studies have solidified the ability of OCT to assess change in retinal structure. Continued accrual of clinical trial and observational data is needed to validate the use of OCT in clinical trials, but preliminary work suggests that an intereye difference in retinal nerve fiber layer thickness of 5-6 µm is a clinically meaningful threshold that identifies an optic nerve lesion in MS. CONCLUSIONS: Visual impairment represents a significant component of overall disability in MS. LCLA and OCT enhance the detection of visual pathway injury and can be used as measures of axonal and neuronal integrity. Continued investigation is ongoing to further incorporate these vision-based assessments into clinical trials of MS therapies.

Rapid Number Naming and Quantitative Eye Movements May Reflect Contact Sport Exposure in a Collegiate Ice Hockey Cohort.

BACKGROUND: The King-Devick (K-D) test of rapid number naming is a reliable visual performance measure that is a sensitive sideline indicator of concussion when time scores worsen (lengthen) from preseason baseline. Within cohorts of youth athletes <18 years old, baseline K-D times become faster with increasing age. We determined the relation of rapid number-naming time scores on the K-D test to electronic measurements of saccade performance during preseason baseline assessments in a collegiate ice hockey team cohort. Within this group of young adult athletes, we also sought to examine the potential role for player age in determining baseline scores. METHODS: Athletes from a collegiate ice hockey team received preseason baseline testing as part of an ongoing study of rapid rink-side performance measures for concussion. These included the K-D test (spiral-bound cards and tablet computer versions). Participants also performed a laboratory-based version of the K-D test with simultaneous infrared-based video-oculographic recordings using an EyeLink 1000+. This allowed measurement of the temporal and spatial characteristics of eye movements, including saccadic velocity, duration, and intersaccadic interval (ISI). RESULTS: Among 13 male athletes, aged 18-23 years (mean 20.5 ± 1.6 years), prolongation of the ISI (a combined measure of saccade latency and fixation duration) was the measure most associated with slower baseline time scores for the EyeLink-paired K-D (mean 38.2 ± 6.2 seconds, r = 0.88 [95% CI 0.63-0.96], P = 0.0001), the K-D spiral-bound cards (36.6 ± 5.9 seconds, r = 0.60 [95% CI 0.08-0.87], P = 0.03), and K-D computerized tablet version (39.1 ± 5.4 seconds, r = 0.79 [95% CI 0.42-0.93], P = 0.001). In this cohort, older age was a predictor of longer (worse) K-D baseline time performance (age vs EyeLink-paired K-D: r = 0.70 [95% CI 0.24-0.90], P = 0.008; age vs K-D spiral-bound cards: r = 0.57 [95% CI 0.03-0.85], P = 0.04; age vs K-D tablet version: r = 0.59 [95% CI 0.06-0.86], P = 0.03) as well as prolonged ISI (r = 0.62 [95% CI 0.11-0.87], P = 0.02). Slower baseline K-D times were not associated with greater numbers of reported prior concussions. CONCLUSIONS: Rapid number-naming performance using the K-D at preseason baseline in this small cohort of collegiate ice hockey players is best correlated with ISI among eye movement-recording measures. Baseline K-D scores notably worsened with increasing age, but not with numbers of prior concussions in this small cohort. While these findings require further investigation by larger studies of contact and noncontact sports athletes, they suggest that duration of contact sports exposure may influence preseason test performance.

Validity of low-resolution eye-tracking to assess eye movements during a rapid number naming task: performance of the eyetribe eye tracker.

OBJECTIVE: To evaluate the performance of the EyeTribe compared to the EyeLink for eye movement recordings during a rapid number naming test in healthy control participants. BACKGROUND: With the increasing accessibility of portable, economical, video-based eye trackers such as the EyeTribe, there is growing interest in these devices for eye movement recordings, particularly in the domain of sports-related concussion. However, prior to implementation there is a primary need to establish the validity of these devices. One current limitation of portable eye trackers is their sampling rate (30-60 samples per second, or Hz), which is typically well below the benchmarks achieved by their research-grade counterparts (e.g., the EyeLink, which samples at 500-2000 Hz). METHODS: We compared video-oculographic measurements made using the EyeTribe with those of the EyeLink during a digitized rapid number naming task (the King-Devick test) in a convenience sample of 30 controls. RESULTS: EyeTribe had loss of signal during recording, and failed to reproduce the typical shape of saccadic main sequence relationships. In addition, EyeTribe data yielded significantly fewer detectable saccades and displayed greater variance of inter-saccadic intervals than the EyeLink system. CONCLUSION: Caution is advised prior to implementation of low-resolution eye trackers for objective saccade assessment and sideline concussion screening.

The effect of linguistic background on rapid number naming: implications for native versus non-native English speakers on sideline-focused concussion assessments.

OBJECTIVE: To determine if native English speakers (NES) perform differently compared to non-native English speakers (NNES) on a sideline-focused rapid number naming task. A secondary aim was to characterize objective differences in eye movement behaviour between cohorts. BACKGROUND: The King-Devick (KD) test is a rapid number-naming task in which numbers are read from left-to-right. This performance measure adds vision-based assessment to sideline concussion testing. Reading strategies differ by language. Concussion may also impact language and attention. Both factors may affect test performance. METHODS: Twenty-seven healthy  NNES and healthy NES performed a computerized KD test under high-resolution video-oculography.  NNES also performed a Bilingual Dominance Scale (BDS) questionnaire to weight linguistic preferences (i.e., reliance on non-English language(s)). RESULTS: Inter-saccadic intervals were significantly longer in  NNES (346.3 ± 78.3 ms vs. 286.1 ± 49.7 ms, p = 0.001), as were KD test times (54.4 ± 15.1 s vs. 43.8 ± 8.6 s, p = 0.002). Higher BDS scores, reflecting higher native language dominance, were associated with longer inter-saccadic intervals in  NNES. CONCLUSION: These findings have direct implications for the assessment of athlete performance on vision-based and other verbal sideline concussion tests; these results are particularly important given the international scope of sport. Pre-season baseline scores are essential to evaluation in the event of concussion, and performance of sideline tests in the athlete's native language should be considered to optimize both baseline and post-injury test accuracy.

A nonlinear generalization of the Savitzky-Golay filter and the quantitative analysis of saccades.

The Savitzky-Golay (SG) filter is widely used to smooth and differentiate time series, especially biomedical data. However, time series that exhibit abrupt departures from their typical trends, such as sharp waves or steps, which are of physiological interest, tend to be oversmoothed by the SG filter. Hence, the SG filter tends to systematically underestimate physiological parameters in certain situations. This article proposes a generalization of the SG filter to more accurately track abrupt deviations in time series, leading to more accurate parameter estimates (e.g., peak velocity of saccadic eye movements). The proposed filtering methodology models a time series as the sum of two component time series: a low-frequency time series for which the conventional SG filter is well suited, and a second time series that exhibits instantaneous deviations (e.g., sharp waves, steps, or more generally, discontinuities in a higher order derivative). The generalized SG filter is then applied to the quantitative analysis of saccadic eye movements. It is demonstrated that (a) the conventional SG filter underestimates the peak velocity of saccades, especially those of small amplitude, and (b) the generalized SG filter estimates peak saccadic velocity more accurately than the conventional filter.

Effect of blocking tactile information from the fingertips on adaptation and execution of grip forces to friction at the grasping surface.

Adaptation of fingertip forces to friction at the grasping surface is necessary to prevent use of inadequate or excessive grip forces. In the current study we investigated the effect of blocking tactile information from the fingertips noninvasively on the adaptation and efficiency of grip forces to surface friction during precision grasp. Ten neurologically intact subjects grasped and lifted an instrumented grip device with 18 different frictional surfaces under three conditions: with bare hands or with a thin layer of plastic (Tegaderm) or an additional layer of foam affixed to the fingertips. The coefficient of friction at the finger-object interface of each surface was obtained for each subject with bare hands and Tegaderm by measuring the slip ratio (grip force/load force) at the moment of slip. We found that the foam layer reduced sensibility for two-point discrimination and pressure sensitivity at the fingertips, but Tegaderm did not. However, Tegaderm reduced static, but not dynamic, tactile discrimination. Adaptation of fingertip grip forces to surface friction measured by the rate of change of peak grip force, and grip force efficiency measured by the grip-load force ratio at lift, showed a proportional relationship with bare hands but were impaired with Tegaderm and foam. Activation of muscles engaged in precision grip also varied with the frictional surface with bare hands but not with Tegaderm and foam. The results suggest that sensitivity for static tactile discrimination is necessary for feedforward and feedback control of grip forces and for adaptive modulation of muscle activity during precision grasp.

The visual perception of natural motion: abnormal task-related neural activity in DYT1 dystonia.

Although primary dystonia is defined by its characteristic motor manifestations, non-motor signs and symptoms have increasingly been recognized in this disorder. Recent neuroimaging studies have related the motor features of primary dystonia to connectivity changes in cerebello-thalamo-cortical pathways. It is not known, however, whether the non-motor manifestations of the disorder are associated with similar circuit abnormalities. To explore this possibility, we used functional magnetic resonance imaging to study primary dystonia and healthy volunteer subjects while they performed a motion perception task in which elliptical target trajectories were visually tracked on a computer screen. Prior functional magnetic resonance imaging studies of healthy subjects performing this task have revealed selective activation of motor regions during the perception of 'natural' versus 'unnatural' motion (defined respectively as trajectories with kinematic properties that either comply with or violate the two-thirds power law of motion). Several regions with significant connectivity changes in primary dystonia were situated in proximity to normal motion perception pathways, suggesting that abnormalities of these circuits may also be present in this disorder. To determine whether activation responses to natural versus unnatural motion in primary dystonia differ from normal, we used functional magnetic resonance imaging to study 10 DYT1 dystonia and 10 healthy control subjects at rest and during the perception of 'natural' and 'unnatural' motion. Both groups exhibited significant activation changes across perceptual conditions in the cerebellum, pons, and subthalamic nucleus. The two groups differed, however, in their responses to 'natural' versus 'unnatural' motion in these regions. In healthy subjects, regional activation was greater during the perception of natural (versus unnatural) motion (P < 0.05). By contrast, in DYT1 dystonia subjects, activation was relatively greater during the perception of unnatural (versus natural) motion (P < 0.01). To explore the microstructural basis for these functional changes, the regions with significant interaction effects (i.e. those with group differences in activation across perceptual conditions) were used as seeds for tractographic analysis of diffusion tensor imaging scans acquired in the same subjects. Fibre pathways specifically connecting each of the significant functional magnetic resonance imaging clusters to the cerebellum were reconstructed. Of the various reconstructed pathways that were analysed, the ponto-cerebellar projection alone differed between groups, with reduced fibre integrity in dystonia (P < 0.001). In aggregate, the findings suggest that the normal pattern of brain activation in response to motion perception is disrupted in DYT1 dystonia. Thus, it is unlikely that the circuit changes that underlie this disorder are limited to primary sensorimotor pathways.

Effects of emotionally charged auditory stimulation on gait performance in the elderly: a preliminary study.

OBJECTIVES: To evaluate the effect of a novel divided attention task-walking under auditory constraints-on gait performance in older adults and to determine whether this effect was moderated by cognitive status. DESIGN: Validation cohort. SETTING: General community. PARTICIPANTS: Ambulatory older adults without dementia (N=104). INTERVENTIONS: Not applicable. MAIN OUTCOME MEASURES: In this pilot study, we evaluated walking under auditory constraints in 104 older adults who completed 3 pairs of walking trials on a gait mat under 1 of 3 randomly assigned conditions: 1 pair without auditory stimulation and 2 pairs with emotionally charged auditory stimulation with happy or sad sounds. RESULTS: The mean age of subjects was 80.6±4.9 years, and 63% (n=66) were women. The mean velocity during normal walking was 97.9±20.6cm/s, and the mean cadence was 105.1±9.9 steps/min. The effect of walking under auditory constraints on gait characteristics was analyzed using a 2-factorial analysis of variance with a 1-between factor (cognitively intact and minimal cognitive impairment groups) and a 1-within factor (type of auditory stimuli). In both happy and sad auditory stimulation trials, cognitively intact older adults (n=96) showed an average increase of 2.68cm/s in gait velocity (F1.86,191.71=3.99; P=.02) and an average increase of 2.41 steps/min in cadence (F1.75,180.42=10.12; P<.001) as compared with trials without auditory stimulation. In contrast, older adults with minimal cognitive impairment (Blessed test score, 5-10; n=8) showed an average reduction of 5.45cm/s in gait velocity (F1.87,190.83=5.62; P=.005) and an average reduction of 3.88 steps/min in cadence (F1.79,183.10=8.21; P=.001) under both auditory stimulation conditions. Neither baseline fall history nor performance of activities of daily living accounted for these differences. CONCLUSIONS: Our results provide preliminary evidence of the differentiating effect of emotionally charged auditory stimuli on gait performance in older individuals with minimal cognitive impairment compared with those without minimal cognitive impairment. A divided attention task using emotionally charged auditory stimuli might be able to elicit compensatory improvement in gait performance in cognitively intact older individuals, but lead to decompensation in those with minimal cognitive impairment. Further investigation is needed to compare gait performance under this task to gait on other dual-task paradigms and to separately examine the effect of physiological aging versus cognitive impairment on gait during walking under auditory constraints.