Evidence of elevated situational awareness for active duty soldiers during navigation of a virtual environment.

U.S. service members maintain constant situational awareness (SA) due to training and experience operating in dynamic and complex environments. Work examining how military experience impacts SA during visual search of a complex naturalistic environment, is limited. Here, we compare Active Duty service members and Civilians' physiological behavior during a navigational visual search task in an open-world virtual environment (VE) while cognitive load was manipulated. We measured eye-tracking and electroencephalogram (EEG) outcomes from Active Duty (N = 21) and Civilians (N = 15) while they navigated a desktop VE at a self-regulated pace. Participants searched and counted targets (N = 15) presented among distractors, while cognitive load was manipulated with an auditory Math Task. Results showed Active Duty participants reported significantly greater/closer to the correct number of targets compared to Civilians. Overall, Active Duty participants scanned the VE with faster peak saccade velocities and greater average saccade magnitudes compared to Civilians. Convolutional Neural Network (CNN) response (EEG P-300) was significantly weighted more to initial fixations for the Active Duty group, showing reduced attentional resources on object refixations compared to Civilians. There were no group differences in fixation outcomes or overall CNN response when comparing targets versus distractor objects. When cognitive load was manipulated, only Civilians significantly decreased their average dwell time on each object and the Active Duty group had significantly fewer numbers of correct answers on the Math Task. Overall, the Active Duty group explored the VE with increased scanning speed and distance and reduced cognitive re-processing on objects, employing a different, perhaps expert, visual search strategy indicative of increased SA. The Active Duty group maintained SA in the main visual search task and did not appear to shift focus to the secondary Math Task. Future work could compare how a stress inducing environment impacts these groups' physiological or cognitive markers and performance for these groups.

Gaze Behavior During Navigation and Visual Search of an Open-World Virtual Environment.

Eye tracking has been an essential tool within the vision science community for many years. However, the majority of studies involving eye-tracking technology employ a relatively passive approach through the use of static imagery, prescribed motion, or video stimuli. This is in contrast to our everyday interaction with the natural world where we navigate our environment while actively seeking and using task-relevant visual information. For this reason, an increasing number of vision researchers are employing virtual environment platforms, which offer interactive, realistic visual environments while maintaining a substantial level of experimental control. Here, we recorded eye movement behavior while subjects freely navigated through a rich, open-world virtual environment. Within this environment, subjects completed a visual search task where they were asked to find and count occurrence of specific targets among numerous distractor items. We assigned each participant into one of four target conditions: Humvees, motorcycles, aircraft, or furniture. Our results show a statistically significant relationship between gaze behavior and target objects across Target Conditions with increased visual attention toward assigned targets. Specifically, we see an increase in the number of fixations and an increase in dwell time on target relative to distractor objects. In addition, we included a divided attention task to investigate how search changed with the addition of a secondary task. With increased cognitive load, subjects slowed their speed, decreased gaze on objects, and increased the number of objects scanned in the environment. Overall, our results confirm previous findings and support that complex virtual environments can be used for active visual search experimentation, maintaining a high level of precision in the quantification of gaze information and visual attention. This study contributes to our understanding of how individuals search for information in a naturalistic (open-world) virtual environment. Likewise, our paradigm provides an intriguing look into the heterogeneity of individual behaviors when completing an un-timed visual search task while actively navigating.

Effects of Neurocognitive Temporal Training on Weapon Firing Performance.

While marksmanship is a critical skill for military personnel, some service members experience difficulty in attaining and maintaining marksmanship qualifications. Temporal training may improve marksmanship performance, since rhythm and timing are critical for coordinated movement. In this study, we examined the effect of neurocognitive temporal training (NTT) on military personnel's marksmanship performance. We randomly assigned 41 active duty U.S. Army service members with prior marksmanship training into an NTT group that received 12 NTT training sessions (N = 18) and a Control group (N = 23) that received no NTT training. We measured marksmanship at baseline (pretest) and following either NTT (posttest) or, for the Control group, a comparable time period. We quantified marksmanship during 2 tasks of firing 5 self-paced shots at stationary 175 m and 300 m targets (Task 1) and firing at 50 moving and stationary targets of varying distances (Task 2). We recorded three measures of accuracy and three measures of precision (including Total Path Length, a unique measure quantifying shot-to-shot variability) for the first task, and we recorded one accuracy measure for the second task. To determine group differences for pretest versus posttest, we used multivariate analysis of variances for Task 1 and a mixed-model analysis of variance for Task 2. Results revealed significantly reduced variability and improved precision when firing at the 175 m target for the NTT group compared with the Control group (p < .05), but there were no significant group differences on other measures. While these results suggest the utility of neurocognitive timing and rhythm training for marksmanship precision, additional research is needed and should include varied training regimens, comparisons of expert versus novice shooters, additional outcome measures, and a larger participant sample.

Phase I Safety Trial: Extended Daily Peripheral Sensory Stimulation Using a Wrist-Worn Vibrator in Stroke Survivors.

Peripheral sensory stimulation augments post-stroke upper extremity rehabilitation outcomes. Most sensory stimulations interfere with natural hand tasks and the stimulation duration is limited. We developed TheraBracelet, low-level random-frequency vibration applied via a wristwatch, to enable stimulation during hand tasks and potentially extend stimulation durations. To determine safety of prolonged exposure to TheraBracelet. Single-site double-blind crossover randomized controlled trial. Chronic stroke survivors were instructed to wear a device on the affected wrist for > 8 h/day everyday for 2 months while coming to the laboratory weekly for evaluations, with a 2-week break between each month. The device applied vibration at 60% and 1% of the sensory threshold for the real and sham month, respectively. The order of the real and sham months was randomized/balanced. Adverse events (AEs) were assessed weekly, including worsening of hand sensation, dexterity, grip strength, pain, or spasticity and occurrence of skin irritation or swelling. Device-related AE rates were compared between the real and sham month. Twenty-five participants completed the study. Six participants (24%) experienced mild AEs involving worsened sensory scores that may be related to the intervention with reasonable possibility. Two experienced them in the real stimulation month only, 3 in the sham month only, and 1 in both months. Therefore, less participants experienced device-related AEs in the real than sham month. Daily stimulation using the device for a month is safe for chronic stroke survivors. Future studies examining the efficacy of pairing TheraBracelet with therapy for increasing neurorehabilitation outcomes are a logical next step. Trial registration: NCT03318341.

Effects of Sensory Deficit on Phalanx Force Deviation During Power Grip Post Stroke.

The effect of sensory deficits on power grip force from individual phalanges was examined. The authors found that stroke survivors with sensory deficits (determined by the Semmes-Weinstein monofilament test) gripped with phalanx force directed more tangential to the object surface, than those without, although both groups had similar motor deficits (Chedoke-McMaster and Fugl-Meyer), grip strength, and skin friction. Altered grip force direction elevates risk of finger slippage against the object thus grip loss/object dropping, hindering activities of daily living. Altered grip force direction was associated with altered muscle activation patterns. In summary, the motor impairment level alone may not describe hand motor control in detail. Information about sensory deficits helps elucidate patients' hand motor control with functional relevance.

Altered phalanx force direction during power grip following stroke.

Many stroke survivors with severe impairment can grasp only with a power grip. Yet, little knowledge is available on altered power grip after stroke, other than reduced power grip strength. This study characterized stroke survivors' static power grip during 100 and 50 % maximum grip. Each phalanx force angular deviation from the normal direction and its contribution to total normal force was compared for 11 stroke survivors and 11 age-matched controls. Muscle activities and skin coefficient of friction were additionally compared for another 20 stroke and 13 age-matched control subjects. The main finding was that stroke survivors gripped with a 34 % greater phalanx force angular deviation of 19° ± 2° compared to controls of 14° ± 1° (p < .05). Stroke survivors' phalanx force angular deviation was closer to the 23° threshold of slippage between the phalanx and grip surface, which may explain increased likelihood of object dropping in stroke survivors. In addition, this altered phalanx force direction decreases normal grip force by tilting the force vector, indicating a partial role of phalanx force angular deviation in reduced grip strength post-stroke. Greater phalanx force angular deviation may biomechanically result from more severe underactivation of stroke survivors' first dorsal interosseous and extensor digitorum communis muscles compared to their flexor digitorum superficialis or somatosensory deficit. While stroke survivors' maximum power grip strength was approximately half of the controls, the distribution of their remaining strength over the fingers and phalanges did not differ, indicating evenly distributed grip force reduction over the entire hand.

The extent of altered digit force direction correlates with clinical upper extremity impairment in chronic stroke survivors.

Many stroke survivors suffer from impaired hand function. Biomechanics of hand grip suggests that abnormally directed grip force can hamper gripping abilities and hand function. This study examined the relation between the ability to precisely direct fingertip force and clinical hand function scores among individuals affected by stroke. Specifically, clinical hand function tests of the Fugl-Meyer, Chedoke McMaster, and Box and Block Test were used, since they involve various hand movements required for activities of daily living. Digit force direction during static grip was recorded using multiaxial load cells. Data for 59 chronic stroke survivors were analyzed. We found that larger angular deviation of digit force from the normal direction was significantly associated with lower hand functional levels (p<.001 for all three clinical tests). Particularly, stroke survivors whose digit force deviated more than 21° from the normal direction could not achieve the normal level of Fugl-Meyer or Chedoke or move more than 4 blocks in a minute. The biomechanics of the way digit force direction affects hand grip function is described. In addition, underlying mechanisms for altered digit force direction post stroke are postulated, including impaired somatosensation and abnormal neural input to muscles. In summary, this study identifies a new biomechanical marker for hand functional level and recovery. Future interventions may focus on correcting digit force direction to improve hand functional outcome.

Effect of remote sensory noise on hand function post stroke.

Hand motor impairment persists after stroke. Sensory inputs may facilitate recovery of motor function. This pilot study tested the effectiveness of tactile sensory noise in improving hand motor function in chronic stroke survivors with tactile sensory deficits, using a repeated measures design. Sensory noise in the form of subthreshold, white noise, mechanical vibration was applied to the wrist skin during motor tasks. Hand dexterity assessed by the Nine Hole Peg Test and the Box and Block Test and pinch strength significantly improved when the sensory noise was turned on compared with when it was turned off in chronic stroke survivors. The subthreshold sensory noise to the wrist appears to induce improvements in hand motor function possibly via neuronal connections in the sensoriomotor cortex. The approach of applying concomitant, unperceivable mechanical vibration to the wrist during hand motor tasks is easily adoptable for clinic use as well as unsupervised home use. This pilot study suggests a potential for a wristband-type assistive device to complement hand rehabilitation for stroke survivors with sensorimotor deficit.

Improvement of hand function using different surfaces and identification of difficult movement post stroke in the Box and Block Test.

This study determined the impact of changing block surfaces on hand function, as well as identified particularly time-consuming movement components post stroke, measured by the Box and Block Test (BBT). Eight chronic stroke survivors and eight age- and gender-matched control subjects participated in this study. The BBT score (number of blocks moved) and time for seven movement components were compared for three different block surfaces (wood, paper, and rubber). The rubber blocks improved BBT scores 8% (compared to all other conditions) not only for control subjects but also for the paretic and non-paretic hands of stroke survivors, by reducing movement time for finger closing and contact-to-lift. Modifying daily objects' surfaces with rubber could help stroke survivors' hand function. The paretic hand displayed notably slower movement for contact-to-lift, transport-release, reach before barrier, and reach after barrier suggesting that therapies may focus on goal directed reaching and object grasping/releasing.

Remote vibrotactile noise improves light touch sensation in stroke survivors' fingertips via stochastic resonance.

BACKGROUND AND PURPOSE: Stroke rehabilitation does not often integrate both sensory and motor recovery. While subthreshold noise was shown to enhance sensory signal detection at the site of noise application, having a noise-generating device at the fingertip to enhance fingertip sensation and potentially enhance dexterity for stroke survivors is impractical, since the device would interfere with object manipulation. This study determined if remote application of subthreshold vibrotactile noise (away from the fingertips) improves fingertip tactile sensation with potential to enhance dexterity for stroke survivors. METHODS: Index finger and thumb pad sensation was measured for ten stroke survivors with fingertip sensory deficit using the Semmes-Weinstein Monofilament and Two-Point Discrimination Tests. Sensation scores were measured with noise applied at one of three intensities (40%, 60%, 80% of the sensory threshold) to one of four locations of the paretic upper extremity (dorsal hand proximal to the index finger knuckle, dorsal hand proximal to the thumb knuckle, dorsal wrist, volar wrist) in a random order, as well as without noise at beginning (Pre) and end (Post) of the testing session. RESULTS: Vibrotactile noise of all intensities and locations instantaneously and significantly improved Monofilament scores of the index fingertip and thumb tip (p < .01). No significant effect of the noise was seen for the Two-Point Discrimination Test scores. CONCLUSIONS: Remote application of subthreshold (imperceptible) vibrotactile noise at the wrist and dorsal hand instantaneously improved stroke survivors' light touch sensation, independent of noise location and intensity. Vibrotactile noise at the wrist and dorsal hand may have enhanced the fingertips' light touch sensation via stochastic resonance and interneuronal connections. While long-term benefits of noise in stroke patients warrants further investigation, this result demonstrates potential that a wearable device applying vibrotactile noise at the wrist could enhance sensation and grip ability without interfering with object manipulation in everyday tasks.

Hand grip function assessed by the box and block test is affected by object surfaces.

STUDY DESIGN: N/A. BACKGROUND: One of the hand function assessment tools is the Box and Block Test (BBT). PURPOSE: To examine if the BBT score is affected by grip surfaces. METHODS: Thirteen adults performed the BBT with wooden, rubber-covered, and paper-covered blocks. The BBT scores and time for seven movements (finger closing, contact to lift-off, transport before barrier, transport after barrier, release, return, and reach) were compared across the three block types. RESULTS: The mean BBT score was 8% higher for the rubber blocks than the paper and wooden blocks (p<0.01) due to the reduced time for contact to lift-off (when the finger touches a block until the block is lifted). CONCLUSIONS: Hand function assessments should be controlled for object surfaces. Therapists may vary grip difficulties by changing object surfaces. Redesigning daily objects with high-friction surfaces may increase grip function. LEVEL OF EVIDENCE: N/A.

Phalanx force magnitude and trajectory deviation increased during power grip with an increased coefficient of friction at the hand-object interface.

This study examined the effect of friction between the hand and grip surface on a person's grip strategy and force generation capacity. Twelve young healthy adults performed power grip exertions on an instrumented vertical cylinder with the maximum and 50% of maximum efforts (far above the grip force required to hold the cylinder), while normal and shear forces at each phalanx of all five fingers in the direction orthogonal to the gravity were recorded. The cylinder surface was varied for high-friction rubber and low-friction paper coverings. An increase in surface friction by replacing the paper covering with the rubber covering resulted in 4% greater mean phalanx normal force (perpendicular to the cylinder surface) and 22% greater mean phalanx shear force in either the proximal or distal direction of the digits (p<0.05; for both 50% and maximum grip efforts). Consequently, increased friction with the rubber surface compared to the paper surface was associated with a 20% increase in the angular deviation of the phalanx force from the direction normal to the cylinder surface (p<0.05). This study demonstrates that people significantly changed the magnitude and direction of phalanx forces depending on the surface they gripped. Such change in the grip strategy appears to help increase grip force generation capacity. This finding suggests that a seemingly simple power grip exertion involves sensory feedback-based motor control, and that people's power grip capacity may be reduced in cases of numbness, glove use, or injuries resulting in reduced sensation.

Grip surface affects maximum pinch force.

OBJECTIVE: The aim of this study was to investigate whether people change their isometric pinch grip generation depending on the surface they gripped. Specifically, the effect of grip surface friction condition on (a) maximum force produced in the direction normal to the contact surface, (b) fluctuation of normal force, and (c) the digit force's angular deviation from the direction normal to the grip surface was quantified. BACKGROUND: Isometric pinch grip has been traditionally thought to be independent from the friction condition between the finger and gripped surface, which may be questionable. METHOD: For this study, 12 healthy participants performed maximum isometric pinch grip exertion on high-friction rubber and low-friction paper surfaces. Maximum normal force, normal force variance,and digit force's angular deviation from the normal direction were quantified. RESULTS: Pinch grip on the high-friction rubber surface was associated with 10% greater maximum normal force and 50% reduced normal force variance, compared with the low-friction paper surface (p < .05). Digit force's angular deviation was not significantly different between the two surface friction conditions. CONCLUSION: The data support that people do change their pinch grip generation (maximum normal force and normal force variance) depending on the surface they gripped, potentially by using sensory feedback. The results of this study demonstrate that even a simple isometric pinch grip (no lifting associated) is affected by grip surface friction. APPLICATION: Grip surface condition should be considered for clinical assessments, biomechanical investigation, and motor control studies to ensure consistency in measurements and validity of comparisons.