Movement Variability Research Articles

Spatial Variability of Movement, Structure, and Formation of Warm Core Rings in the Northwest Atlantic Slope Sea

AbstractGulf Stream Warm Core Rings (WCRs) have important influences on the New England Shelf and marine ecosystems. A 10‐year (2011–2020) WCR dataset that tracks weekly WCR locations and surface areas is used here to identify the rings' path and characterize their movement between 55 and 75°W. The WCR dataset reveals a very narrow band between 66 and 71°W along which rings travel almost due west along ∼39°N across isobaths – the “Ring Corridor.” Then, west of the corridor, the mean path turns southwestward, paralleling the shelfbreak. The average ring translation speed along the mean path is 5.9 cm s−1. Long‐lived rings (lifespan >150 days) tend to occupy the region west of the New England Seamount Chain (NESC) whereas short‐lived rings (lifespan <150 days) tend to be more broadly distributed. WCR vertical structures, analyzed using available Argo float profiles indicate that rings that are formed to the west of the NESC have shallower thermoclines than those formed to the east. This tendency may be due to different WCR formation processes that are observed to occur along different sections of the Gulf Stream. WCRs formed to the east of the NESC tend to form from a pinch‐off mechanism incorporating cores of Sargasso Sea water and a perimeter of Gulf Stream water. WCRs that form to the west of the NESC, form from a process called an aneurysm. WCRs formed through aneurysms comprise water mostly from the northern half of the Gulf Stream and are smaller than the classic pinch‐off rings.

Beyond Efficiency: Surface Electromyography Enables Further Insights into the Surgical Movements of Urologists

Introduction: Surgical skill evaluation while performing minimally invasive surgeries is a highly complex task. It is important to objectively assess an individual's technical skills throughout surgical training to monitor progress and to intervene when skills are not commensurate with the year of training. The miniaturization of wireless wearable platforms integrated with sensor technology has made it possible to noninvasively assess muscle activations and movement variability during performance of minimally invasive surgical tasks. Our objective was to use electromyography (EMG) to deconstruct the motions of a surgeon during robotic suturing (RS) and distinguish quantifiable movements that characterize the skill of an experienced expert urologic surgeon from trainees. Methods: Three skill groups of participants, novice (n = 11), intermediate (n = 12), and expert (n = 3), were enrolled in the study. A total of 12 wireless wearable sensors consisting of surface EMGs and accelerometers were placed along upper extremity muscles to assess muscle activations and movement variability, respectively. Participants then performed a RS task. Results: EMG-based parameters, total time, dominant frequency, and cumulative muscular workload, were significantly different across the three skill groups. We also found nonlinear movement variability parameters such as correlation dimension, Lyapunov exponent trended differently across the three skill groups. Conclusions: These findings suggest that economy of motion variables and nonlinear movement variabilities are affected by surgical experience level. Wearable sensor signal analysis could make it possible to objectively evaluate surgical skill level periodically throughout the residency training experience. Clinical Trial Registration Number: HS# 2018-4407.

Low Gain Values of the Vestibulo-Ocular Reflex Can Optimize Retinal Image Slip.

The angular vestibulo-ocular reflex (aVOR) stabilizes retinal images by counter-rotating the eyes during head rotations. Perfect compensatory movements would thus rotate the eyes exactly opposite to the head, that is, eyes vs. head would exhibit a unity gain. However, in many species, but also in elderly humans or patients with a history of vestibular damage, the aVOR is far from compensatory with gains that are in part considerably lower than unity. The reason for this apparent suboptimality is unknown. Here, we propose that low VOR gain values reflect an optimal adaptation to sensory and motor signal variability. According to this hypothesis, gaze stabilization mechanisms that aim at minimizing the overall retinal image slip must consider the effects of (1) sensory and motor noise and (2) dynamic constraints of peripheral and central nervous processing. We demonstrate that a computational model for optimizing retinal image slip in the presence of such constraints of signal processing in fact predicts gain values smaller than unity. We further show specifically for tadpoles of the clawed toad, Xenopus laevis with particularly low gain values that previously reported VOR gains quantitatively correspond to the observed variability of eye movements and thus constitute an optimal adaptation mechanism. We thus hypothesize that lower VOR gain values in elderly human subjects or recovered patients with a history of vestibular damage may be the sign of an optimization given higher noise levels rather than a direct consequence of the damage, such as an inability of executing fast compensatory eye movements.

Electro-suit treatment of children with unilateral cerebral palsy alters nonlinear dynamics of walking

BackgroundCerebral palsy (CP) is characterized by spasticity and muscle contracture development and associated with mild to severe motor impairments including reduced gait function. Treatment with the Exopulse® suit has been shown to reduce spasticity of the affected muscles and constitutes a non-invasive alternative to pharmaceutical agents and surgical denervation. The present study investigated the effect of systematic treatment with the Exopulse® suit on the nonlinear dynamics and variability of trunk accelerations during walking in children with unilateral CP. MethodsTwelve patients (mean age: 12 years, range 7–17 years) with unilateral CP (GMFCS level 1 and 2) received 24 weeks Exopulse® suit treatment with patient-specific muscle stimulation. Before and after the treatment, the patients completed 4 min treadmill walking while trunk accelerometry was obtained. The nonlinear dynamics was quantified by the largest Lyapunov exponent and the complexity index from the multiscale entropy and movement variability was quantified by the root mean square ratio. Pre- vs post-treatment differences were evaluated by a paired Student's t-test. FindingsThe largest Lyapunov exponent (p-value = 0.041) and the complexity index (p-value = 0.030) of the acceleration in the anterior-posterior direction was significantly lower post-treatment. No other between-trial differences were observed. InterpretationThe present study suggests that 24 weeks of Exopulse® suit treatment alters the nonlinear dynamics but not the variability of the trunk accelerations during walking in children with unilateral CP. The temporal structure of the trunk acceleration in the anterior-posterior direction was altered towards that of healthy individuals.

Nicotine promotes the utility of short-term memory during visual search in macaque monkeys.

The central cholinergic system is a major therapeutic target for restoring cognitive functions. Although manipulation of cholinergic signaling is known to alter working memory (WM), the underlying mechanism remains unclear. It is widely accepted that WM consists of multiple functional modules, one storing short-term memory and the other manipulating and utilizing it. A recently developed visual search task and a relevant model can be used to assess multiple components of WM during administration of acetylcholine receptor (AChR)-related substances. The effects of systemic administration of AChR-related agents on WM and eye movements were examined during the oculomotor foraging task. Three monkeys performing the task received an intramuscular injection of saline or the following AChR-related agents: nicotine (24 or 56μg/kg), mecamylamine (nicotinic AChR antagonist, 1.0mg/kg), oxotremorine (muscarinic AChR agonist, 3.0µg/kg), and scopolamine (muscarinic AChR antagonist, 20μg/kg). The task was to find a target among 15 identical objects by making eye movements within 6s. The data were analyzed according to the foraging model that incorporated three parameters. Nicotine and mecamylamine significantly increased the utility but not the capacity of short-term memory, while muscarinic AChR-related agents did not alter any WM parameters. Further regression analyses with a mixed-effect model showed that the beneficial effect of nicotine on memory utility remained after considering eye movement variability, but the beneficial effect of mecamylamine disappeared. Nicotine improves visual search, mainly by increasing the utility of short-term memory, with minimal changes in oculomotor parameters.

Machine Learning Identifies Chronic Low Back Pain Patients from an Instrumented Trunk Bending and Return Test.

Nowadays, the better assessment of low back pain (LBP) is an important challenge, as it is the leading musculoskeletal condition worldwide in terms of years of disability. The objective of this study was to evaluate the relevance of various machine learning (ML) algorithms and Sample Entropy (SampEn), which assesses the complexity of motion variability in identifying the condition of low back pain. Twenty chronic low-back pain (CLBP) patients and 20 healthy non-LBP participants performed 1-min repetitive bending (flexion) and return (extension) trunk movements. Analysis was performed using the time series recorded by three inertial sensors attached to the participants. It was found that SampEn was significantly lower in CLBP patients, indicating a loss of movement complexity due to LBP. Gaussian Naive Bayes ML proved to be the best of the various tested algorithms, achieving 79% accuracy in identifying CLBP patients. Angular velocity of flexion movement was the most discriminative feature in the ML analysis. This study demonstrated that: supervised ML and a complexity assessment of trunk movement variability are useful in the identification of CLBP condition, and that simple kinematic indicators are sensitive to this condition. Therefore, ML could be progressively adopted by clinicians in the assessment of CLBP patients.

Variability, accuracy, and cross-linguistic transfer in bilingual children speaking Jamaican Creole and English

ABSTRACT Due to the lack of normative data about bilingual speech development and limited availability of diagnostic tools optimised for this population, bilingual children under consideration for speech-language services are at an elevated risk of misdiagnosis. In the absence of validated assessment tools, speech-language pathologists may use measures of accuracy and variability of speech production to diagnose suspected speech sound disorders in bilingual children. Research in general motor development suggests that variability and accuracy may trade off in the course of maturation, whereby movement variability spikes before the transition to a more mature stage of motor control. Such variability-accuracy tradeoffs have been described in monolingual speech development but are understudied in bilingual populations, where cross-linguistic transfer occurs. This study aimed to examine variability, accuracy, and cross-linguistic transfer in the speech of 20 bilingual children speaking Jamaican Creole and English. We hypothesised that children who showed higher accuracy in their productions would also exhibit more variable speech, indicating a variability-accuracy tradeoff. The Word Inconsistency Assessment from the Diagnostic Evaluation of Articulation and Phonology was administered to measure accuracy and variability in the English context, where misdiagnosis is likely to occur. Contrary to our hypothesis, we observed that individuals with higher accuracy tended to be less variable in their productions. Future research should examine longitudinal trajectories of accuracy and variability and consider a more culturally-appropriate definition of ‘accuracy’ in documenting bilingual speech sound development.

The legacy of Gerald L. Gottlieb in human movement neuroscience.

In this paper, we review the legacy of Gerald (Gerry) Gottlieb in various fields related to the neural control of human movement. His studies on the myotatic (stretch) reflex and postmyotatic responses to ankle joint perturbations paved the way for current explorations of long-loop reflexes and their role in the control of movement. The dual-strategy hypothesis introduced order into a large body of literature on the triphasic muscle activation patterns seen over a variety of voluntary movements in healthy persons. The dual-strategy hypothesis continues to be important for understanding the performance of subjects with disordered motor control. The principle of linear synergy (covariance of joint torques) was an attempt to solve one of the notorious problems of motor redundancy, which remains an important topic in the field. Gerry's attitude toward the equilibrium-point hypothesis varied between rejection and using it to explore patterns of hypothetical control variables and movement variability. The discovery of reciprocal excitation in healthy neonates fostered other studies of changes in spinal cord physiology as motor skills develop. In addition, studies of people with spasticity and the effects of treatment with intrathecal baclofen were crucial in demonstrating the possibility of unmasking voluntary movements after suppression of the hyperreflexia of spasticity. Gerry Gottlieb contributed a significant body of knowledge that formed a solid foundation from which to study a variety of neurological diseases and their treatments, and a more comprehensive and parsimonious foundation to describe the neural control of human movement.

Evaluation of surgical skill using machine learning with optimal wearable sensor locations.

Evaluation of surgical skills during minimally invasive surgeries is needed when recruiting new surgeons. Although surgeons’ differentiation by skill level is highly complex, performance in specific clinical tasks such as pegboard transfer and knot tying could be determined using wearable EMG and accelerometer sensors. A wireless wearable platform has made it feasible to collect movement and muscle activation signals for quick skill evaluation during surgical tasks. However, it is challenging since the placement of multiple wireless wearable sensors may interfere with their performance in the assessment. This study utilizes machine learning techniques to identify optimal muscles and features critical for accurate skill evaluation. This study enrolled a total of twenty-six surgeons of different skill levels: novice (n = 11), intermediaries (n = 12), and experts (n = 3). Twelve wireless wearable sensors consisting of surface EMGs and accelerometers were placed bilaterally on bicep brachii, tricep brachii, anterior deltoid, flexor carpi ulnaris (FCU), extensor carpi ulnaris (ECU), and thenar eminence (TE) muscles to assess muscle activations and movement variability profiles. We found features related to movement complexity such as approximate entropy, sample entropy, and multiscale entropy played a critical role in skill level identification. We found that skill level was classified with highest accuracy by i) ECU for Random Forest Classifier (RFC), ii) deltoid for Support Vector Machines (SVM) and iii) biceps for Naïve Bayes Classifier with classification accuracies 61%, 57% and 47%. We found RFC classifier performed best with highest classification accuracy when muscles are combined i) ECU and deltoid (58%), ii) ECU and biceps (53%), and iii) ECU, biceps and deltoid (52%). Our findings suggest that quick surgical skill evaluation is possible using wearables sensors, and features from ECU, deltoid, and biceps muscles contribute an important role in surgical skill evaluation.

Outcomes and Hand Use of Reaching Attempts: Comparison of Infants at Risk for Developmental Disability and Infants With Typical Development.

BackgroundInfants at risk for developmental disabilities often show signs of motor delay. Reaching is a skill that can help us identify atypical motor trajectories in early infancy. Researchers have studied performance after onset of reaching, but none have followed infants at risk from pre-reaching to skilled reaching.AimsWe assessed differences in reaching outcomes and hand use as reaching skill emerged in infants at risk for developmental disabilities and with typical development.Methods and ProceduresWe followed infants at risk for developmental disabilities (n = 11) and infants with typical development (n = 21) longitudinally as they developed reaching skill. Infants reached for a toy at midline while sitting in the caregiver’s lap. Video data were coded for reach outcome (miss, touch, partial grasp, and whole-hand grasp) and hand use (right, left, and bilateral).Outcomes and ResultsInfants at risk had a larger proportion of missed reaches across visits compared to infants with typical development. Infants at risk also showed less variability in hand use when grasping over the study period.Conclusion and ImplicationsOur results provide information to support early differences in reaching performance to inform identification of typical and atypical developmental trajectories. Future studies should assess how the missed reaches are different and consider other quantitative measures of movement variability in infants at risk.

Learning and performing: What can theory offer high performance sports practitioners?

Currently, the most prominent motor control theories that underpin the pedagogy of coaches in high performance sport are derived from the discipline of psychology with a dominant focus on internalised control processes for learning and performance. In contrast, ecological dynamics is a contemporary meta-theory focused on the person-environment scale of analysis for understanding human behavior, exemplified by strengthening the relations between each learner and their environment. In this tutorial, we outline key concepts in ecological dynamics that considers learning and performance as being distinct, yet inextricably linked. In our considerations, we raise questions on long-held assumptions about control process theories on learning and performance for practice designs in high performance sports. For example, how useful is inferring learning by describing improved performance as showing more relative permanence, greater stability and consistency, with commensurate lower levels of attention and movement variability? How relevant are traditional ways of measuring learning using retention and transfer tests in high performance sports? What is actually attained in an ecological view of learning, focussed on education of attention and calibration of actions to specifying information present in performance environments? An implication of these issues for high performance sport is that learning needs to be assessed by how well a learner adapts to the specific constraints and demands of a performance context. This key idea has important implications for performance analysis and evaluation in sport.

The influence of goal-directed reaching distance on standing postural control variability in non-disabled individuals

BACKGROUND: Performing everyday standing tasks is relevant to the individuals independence. It is a challenging postural action that requires upper extremity (UE) movements to interact with objects of the environment. Postural movement variability is a strategy of the postural system for exploring postural boundaries during the action. The distance to the target to be reached may affect the variability in postural control parameters. AIM: To test if the variability in postural control parameters is enhanced by reaching beyond the UE-length during a goal-directed standing task. METHOD: Twelve non-disabled adult individuals performed reaching to turn on a light switch (target) while standing, which was placed at 100% and 130% of the UE-length distance. The kinetic data were recorded using a force plate during the UE movement, and the centre of pressure (CoP) displacement variability index was calculated. RESULTS: The variability index of the CoP displacement for reaching was greater at the distance of 130% of UE-length compared to 100% in both anterior-posterior and medial-lateral directions (p = 0.019). No differences in time to complete the task were observed. CONCLUSION: Postural system increases the variability in postural controlling variable CoP displacement for reaching beyond the UE-length while standing. This movement variability helps individuals explore the boundaries of this standing action and may be useful for learning processes and counterbalancing postural disturbances.

A continuous times-series and discrete measure analysis of two individual divers performing the 3½ pike somersault dive

ABSTRACT Springboard diving training is often focused upon skill repetition to establish movement accuracy, stability and consistency. Within-participant study designs provide the ability to understand how individuals create these skills under different movement strategies. IMUs measured angular velocity time-series data of two athletes performing multiple repetitions of forward 3½ somersault pike dives. Functional Principal Component Analyses (fPCA) were performed to examine individual movement structure and variability. The first five fPC’s represented approximately 98% of the variability in angular velocity for both divers. To determine the relative importance of angular velocity variability, Pearson’s correlations for pairwise comparisons were used to assess the relationship between fPC scores and discrete performance variables during takeoff, flight and entry. Divers exhibited a different number and types of significant correlations (International = 4; National = 11). Only one correlation was common for both divers; higher angular velocity during Initial Flight and/or Somersault phases resulted in more vertically aligned entry posture (International: fPC1 r = −0.761, p < 0.05; National: fPC3 r = −0.796, p < 0.01). Findings identify individualised angular velocity time-series structure and kinematic performance variables (International = angular; National = linear) that can be used by coaching/sport science teams to optimisation performance success.

Transition from predictable to variable motor cortex and striatal ensemble patterning during behavioral exploration

Animals can capitalize on invariance in the environment by learning and automating highly consistent actions; however, they must also remain flexible and adapt to environmental changes. It remains unclear how primary motor cortex (M1) can drive precise movements, yet also support behavioral exploration when faced with consistent errors. Using a reach-to-grasp task in rats, along with simultaneous electrophysiological monitoring in M1 and dorsolateral striatum (DLS), we find that behavioral exploration to overcome consistent task errors is closely associated with tandem increases in M1 and DLS neural variability; subsequently, consistent ensemble patterning returns with convergence to a new successful strategy. We also show that compared to reliably patterned intracranial microstimulation in M1, variable stimulation patterns result in significantly greater movement variability. Our results thus indicate that motor and striatal areas can flexibly transition between two modes, reliable neural pattern generation for automatic and precise movements versus variable neural patterning for behavioral exploration.

Exploring the role of the left DLPFC in fatigue during unresisted rhythmic movements

Understanding central fatigue during motor activities is important in neuroscience and different medical fields. The central mechanisms of motor fatigue are known in depth for isometric muscle contractions; however, current knowledge about rhythmic movements and central fatigue is rather scarce. In this study, we explored the role of an executive area (left dorsolateral prefrontal cortex [DLPFC]) in fatigue development during rhythmic movement execution, finger tapping (FT) at the maximal rate, and fatigue after effects on the stability of rhythmic patterns. Participants (n = 19) performed six sets of unresisted FT (with a 3 min rest in‐between). Each set included four interleaved 30 s repetitions of self‐selected (two repetitions) and maximal rate FT (two repetitions) without rest in‐between. Left DLPFC involvement in the task was perturbed by transcranial static magnetic stimulation (tSMS) in two sessions (one real and one sham). Moreover, half of the self‐selected FT repetitions were performed concurrently with a demanding cognitive task, the Stroop test. Compared with sham stimulation, real tSMS stimulation prevented waning in tapping frequency at the maximal rate without affecting perceived levels of fatigue. Participants' engagement in the Stroop test just prior to maximal FT reduced the movement amplitude during this mode of execution. Movement variability at self‐selected rates increased during Stroop execution, especially under fatigue previously induced by maximal FT. Our results indicate cognitive‐motor interactions and a prominent role of the prefrontal cortex in fatigue and the motor control of simple repetitive movement patterns. We suggest the need to approach motor fatigue including cognitive perspectives.

Validation of accelerometry as a digital phenotyping measure of negative symptoms in schizophrenia

Negative symptoms are commonly assessed via clinical rating scales; however, these measures have several inherent limitations that impact validity and utility for their use in clinical trials. Objective digital phenotyping measures that overcome some of these limitations are now available. The current study evaluated the validity of accelerometry (ACL), a passive digital phenotyping method that involves collecting data on the presence, vigor, and variability of movement. Outpatients with schizophrenia (SZ: n = 50) and demographically matched healthy controls (CN: n = 70) had ACL continuously recorded from a smartphone and smartband for 6 days. Active digital phenotyping assessments, including surveys related to activity context, were also collected via 8 daily surveys throughout the 6 day period. SZ participants had lower scores on phone ACL variables reflecting vigor and variability of movement compared to CN. ACL variables demonstrated convergent validity as indicated by significant correlations with active digital phenotyping self-reports of time spent in goal-directed activities and clinical ratings of negative symptoms. The discriminant validity of ACL was demonstrated by low correlations with clinical rating scale measures of positive, disorganized, and total symptoms. Collectively, findings suggest that ACL is a valid objective measure of negative symptoms that may complement traditional approaches to assessing the construct using clinical rating scales.

Instructions on Task Constraints Mediate Perceptual-Motor Search and How Movement Variability Relates to Performance Outcome

Movement variability has been postulated to afford perception of the perceptual motor workspace and to be directly linked to improved performance. Here, we investigated how instructions mediate the search process and the relation between performance outcome and movement variability. We used a novel bimanual force tracking task where zero error was achieved via proportional output between the hands. Participants were either instructed or not as to how to coordinate their force output to achieve this goal, but the goal to minimize error was explained to all participants. The provision of instructions restricted the overall area of the task space that was searched. Moreover, the time dependent properties of the search were influenced; where instructions increased the likelihood that participants would produce a higher force level over practice. Multiple regression revealed that variability was positively correlated with performance outcome, but the strength of this relation was dependent on instructions and individual search strategies. The findings are consistent with the view that information through instructions shapes individual emergent perceptual-motor search strategies that in turn mediate how movement variability relates to performance outcome.

How infant-directed actions enhance infants' attention, learning, and exploration: Evidence from EEG and computational modeling.

When teaching infants new actions, parents tend to modify their movements. Infants prefer these infant-directed actions (IDAs) over adult-directed actions and learn well from them. Yet, it remains unclear how parents' action modulations capture infants' attention. Typically, making movements larger than usual is thought to draw attention. Recent findings, however, suggest that parents might exploit movement variability to highlight actions. We hypothesized that variability in movement amplitude rather than higher amplitude is capturing infants' attention during IDAs. Using EEG, we measured 15-month-olds' brain activity while they were observing action demonstrations with normal, high, or variable amplitude movements. Infants' theta power (4-5Hz) in fronto-central channels was compared between conditions. Frontal theta was significantly higher, indicating stronger attentional engagement, in the variable compared to the other conditions. Computational modelling showed that infants' frontal theta power was predicted best by how surprising each movement was. Thus, surprise induced by variability in movements rather than large movements alone engages infants' attention during IDAs. Infants with higher theta power for variable movements were more likely to perform actions successfully and to explore objects novel in the context of the given goal. This highlights the brain mechanisms by which IDAs enhance infants' attention, learning, and exploration.

Disproportionate and chronic sediment delivery from a fluvially controlled, deep‐seated landslide in Aotearoa New Zealand

AbstractPast research has highlighted the importance of sediment delivery from multiple‐occurrence regional landslide events triggered by storms or earthquakes. Herein, we examine delivery from a more persistent source of sediment, that of a large, slow‐moving landslide in the soft‐rock hill country of Aotearoa New Zealand. We map and monitor the 80‐ha Rangitikei Landslide from 2015 to 2019 using time‐lapse photography, ground surveys, photogrammetry, and piezometers. We show that the landslide can be divided into several zones with distinctive movement patterns, but all zones respond to river erosion. The fastest zone moves more than 10 m per year in a flow‐like fashion, while other zones move 0.01 m per year via slow sliding. Movement occurs all year round, but is two to three times faster in winter and spring. While rainfall and associated groundwater change are commonly attributed to landslide movement patterns, our data show that river flow correlates closely with the weekly to seasonal variability in movement of the landslide toe. This suggests that fluvial erosion can play an important role in the movement dynamics of highly coupled landslides. We estimate an annual sediment yield to the Rangitikei River of at least 40 000 tonnes, in this first quantification of sediment delivery from an active soft‐rock landslide in Aotearoa. This volume implies 7% of the total catchment suspended sediment yield is derived from 0.03% of the contributing catchment area, demonstrating the disproportionate effect of this (and likely other) deep‐seated landslide(s) as a source of sediment in the Rangitikei catchment. Sediment delivery is more continuous than the episodic supply of multiple‐occurrence regional landslide triggering events, and by delivering mostly fine‐grained sediment, it has a potentially large impact on water quality.

Eye and Head Movement Recordings Using Smartphones for Telemedicine Applications: Measurements of Accuracy and Precision.

ObjectiveSmartphones have shown promise in the assessment of neuro-ophthalmologic and vestibular disorders. We have shown that the head impulse test results recorded using our application are comparable with measurements from clinical video-oculography (VOG) goggles. The smartphone uses ARKit's capability to acquire eye and head movement positions without the need of performing a calibration as in most eye-tracking devices. Here, we measure the accuracy and precision of the eye and head position recorded using our application.MethodsWe enrolled healthy volunteers and asked them to direct their eyes, their heads, or both to targets on a wall at known eccentricities while recording their head and eye movements with our smartphone application. We measured the accuracy as the error between the eye or head movement measurement and the location of each target and the precision as the standard deviation of the eye or head position for each of the target positions.ResultsThe accuracy of head recordings (15% error) was overall better than the accuracy of eye recordings (23% error). We also found that the accuracy for horizontal eye movements (17% error) was better than for vertical (27% error). Precision was also better for head movement (0.8 degrees) recordings than eye movement recordings (1.3 degrees) and variability tended to increase with eccentricity.ConclusionOur results provide basic metrics evaluating the utility of smartphone applications in the quantitative assessment of head and eye movements. While the new method may not replace the more accurate dedicated VOG devices, they provide a more accessible quantitative option. It may be advisable to include a calibration recording together with any planned clinical test to improve the accuracy.