Markus H. Muser

Comparing eye movements recorded by search coil and infrared eye tracking

ObjectiveThe performance of a new video-based infrared eye tracker (IR) was compared to the magnetic search coil technique (SC). Since the IR offers interesting possibilities as a diagnostic tool in neuro-ophthalmology, it was investigated whether the new device has overcome shortcomings that were reported from former IR systems.MethodsHorizontal saccades were recorded using the IR and the SC. The IR allowed eye movement recordings at different sampling rates ranging from 250xa0Hz to 1000xa0Hz while the SC recorded at 1000xa0Hz.Results/ConclusionsThe results show that the IR and the SC were in good agreement and produced similar results. In contrast to other studies, the influence of the sampling rate of the IR was small. The saccade main-sequences did not show significant differences. The latency times observed for both systems were mainly in the short-latency range.

Evaluation of a new visco-elastic foam for automotive applications

The geometry and mechanical characteristics of the automotive seat greatly influences the occupant kinematics in rear-end collisions. The head restraint is important particularly with respect to soft tissue neck injuries. While several studies analysed the effect of geometrical properties of head restraints, little is reported on the potential to reduce such injury by changing the material of the head restraint padding, i.e. the underlying foam. This study investigates whether the head restraint foam alone can be tailored to reduce whiplash injury. A newly developed visco-elastic (VE) foam was chosen, because advanced energy absorption properties are expected to produce beneficial effects on the occupant motion. The behaviour of the visco-elastic foam was evaluated by performing impact pendulum tests. The most important novel property of the foam thereby consists of its broad temperature range over which it keeps its advantageous visco-elastic deformation properties, while sustaining the ability to dissipate energy. The tests indicated in particular a broad glass transition temperature resulting in a stable impact behaviour over a temperature range of 5°C to 35°C. Applying this foam as a head restraint padding material, several sled tests using a standard car seat were performed. The tests were conducted to mimic rear-end collisions with a delta-v of 16 km/h. A BioRID dummy was used as a human surrogate. For the seat tested, the change of the foam resulted only in minor changes at room temperature, while the standard foam exhibited adequate performance. Additional changes of the head restraint geometry were shown to have a larger beneficial influence on the occupant kinematics.

Saccadic eye movements after low-dose oral alcohol exposure

OBJECTIVESnThe influence of low-dose alcohol intake on reflexive visually guided saccades was investigated.nnnMETHODSn40 healthy human subjects were orally given alcohol resulting in low-dose alcohol concentration (less than 0.8‰) blood alcohol concentration. Before and after exposure, horizontal saccadic eye movements were recorded at several points in time. The recordings were evaluated with regard to accuracy of the eye movements, latency, the peak eye velocity and the time constant that characterizes the main sequence. The results were compared to recordings from a reference group.nnnRESULTSnIt was found that the saccadic eye movement was clearly altered by low-dose alcohol intake. However, its characteristics were not unambiguously pathological when compared to the reference group, even though the subjects reported a moderate to strong effect of alcohol and there were clear signs of inebriation.nnnCONCLUSIONSnThe findings render the evaluation of saccades unsuitable as a simple test for the detection of low-dose alcohol intake.

Analyzing the Riding Behavior of Recreational Skiers and Snowboarders

Video recordings of a ski slope were used in combination with a video-based tracking software to analyze the riding behavior of skiers and snowboarders. It was shown that the methodology is a powerful tool to measure biomechanical parameters such as the speed and curve radii of individual skiers and snowboarders. A total of 6821 observations was recorded and evaluated. Average riding speeds ranged from 16 to 32 km/h (on the different parts of the slope that were analyzed) with maximum speeds of up to 113 km/h. Average curve radii between 6.2 and 9.3 m were measured.

Saccadic eye movement performance as an indicator of driving ability in elderly drivers

OBJECTIVEnRegular checking of the fitness to drive of elderly car-license holders is required in some countries, and this will become increasingly important as more countries face aging populations. The present study investigated whether the analysis of saccadic eye movements could be used as a screening method for the assessment of driving ability.nnnMETHODSnThree different paradigms (prosaccades, antisaccades, and visuovisual interactive (VVI) saccades) were used to test saccadic eye movements in 144 participants split into four groups: elderly drivers who came to the attention of road authorities for suspected lack of fitness to drive, a group of elderly drivers who served as a comparison group, a group of neurology patients with established brain lesion diagnoses, and a young comparison group. The group of elderly drivers with suspected deficits in driving skills also underwent a medical examination and a practical on-road driving test. The results of the saccadic eye tests of the different groups were compared.nnnRESULTSnAntisaccade results indicated a strong link to driving behaviour: elderly drivers who were not fit to drive exhibited a poor performance on the antisaccade task and the performance in the VVI task was also clearly poorer in this group.nnnCONCLUSIONSnTesting saccadic eye movements appears to be a promising and efficient method for screening large numbers of people such as elderly drivers. This study indicated a link between antisaccade performance and the ability to drive. Hence, measuring saccadic eye movements should be considered as a tool for screening the fitness to drive.

Investigating reaction times and stopping performance of skiers and snowboarders

Abstract On-slope experiments were performed to determine the reaction time of recreational skiers and snowboarders. Volunteers riding a slope were instructed to brake to a complete stop after a visual and acoustic signal. Reaction time and parameters such as the duration of the braking manoeuvre and the corresponding stopping distance were recorded. A total of 70 runs were evaluated, including 37 runs with snowboarders and 33 runs with skiers. The average time until the first observable reaction (reaction time) for all athletes was 420 ms; there was no statistically significant difference between skiers and snowboarders. Participants needed on average an additional 470 ms until they actually started braking. Snowboarders needed significantly more time to prepare for braking than skiers and it took snowboarders significantly longer to stop (p<0.05). In line with these findings, snowboarders also exhibited significantly less deceleration during braking compared to skiers. This study quantifies the reaction times of skiers and snowboarders and provides data related to braking of skiers and snowboarders. This data is useful for the development of injury prevention measures and can be used to ensure reasonable slope design.

Pressure aberrations inside the spinal canal during rear-end impact

Minor soft tissue injuries of the cervical spine increasingly pose problems in public health. Such injuries are conveyed particularly often in rear-end automobile collisions at low impact speeds and it has been established that they may be associated with long-term impairment. As a possible cause for this type of injury it has been hypothesized that pressure pulses induced in cervical fluid compartments during the impact could damage the membrane of spinal nerve cells. To date, animal as well as cadaver experiments performed support this hypothesis. A theoretical analysis has been undertaken in order to investigate the pressure and flow pulse emerging in a cervical fluid compartment under conditions representing rear-end impacts with a Dv of 15 km/h. Using the finite element (FE) method, a three-dimensional model of the cervical spine was developed. The model consists of eight vertebrae (C1-T1), the intervertebral discs, the intervertebral joints, all the major ligaments, most of the neck muscles and the head. Additionally, a typical venous blood vessel was included. To determine the pressure behaviour inside the blood vessel, fluid-structure interaction was taken into account. For the time interval including the development of the S-shape, the pressure pulses were calculated and found to be in qualitative agreement with the reported measurements. The shear stresses acting on the vessel wall can be determined from the associated flow pulses. An extrapolation of the results into the interstitial space where nerve cells are located at this stage does not allow assessment of whether a damage threshold may be reached.

Crash-test dummy and pendulum impact tests of ice hockey boards: greater displacement does not reduce impact

Background One injury mechanism in ice hockey is impact with the boards. We investigated whether more flexible hockey boards would provide less biomechanical loading on impact than did existing (reference) boards. Methods We conducted impact tests with a dynamic pendulum (mass 60u2009kg) and with crash test dummies (ES-2 dummy, 4.76 m/s impact speed). Outcomes were biomechanical loading experienced by a player in terms of head acceleration, impact force to the shoulder, spine, abdomen and pelvis as well as compression of the thorax. Results The more flexible board designs featured substantial displacement at impact. Some so-called flexible boards were displaced four times more than the reference board. The new boards possessed less stiffness and up to 90u2009kg less effective mass, reducing the portion of the board mass a player experienced on impact, compared with boards with a conventional design. Flexible boards resulted in a similar or reduced loading for all body regions, apart from the shoulder. The displacement of a board system did not correlate directly with the biomechanical loading. Conclusions Flexible board systems can reduce the loading of a player on impact. However, we found no correlation between the displacement and the biomechanical loading; accordingly, displacement alone was insufficient to characterise the overall loading of a player and thus the risk of injury associated with board impact. Ideally, the performance of boards is assessed on the basis of parameters that show a good correlation to injury risk.

IMPACT TESTING OF DIFFERENT ICE HOCKEY BOARD DESIGNS

Background Impact to boards is a frequent cause of injury in ice hockey. Improving the board design to reduce the biomechanical loading of a player at impact is one option to prevent injury. Objective Compare the impact performance of different ice hockey boards and investigate whether so-called “flexible” board designs are to be preferred over standard designs. Design Impact testing of ice hockey boards under laboratory conditions using a dynamic pendulum as well as anthropometric test devices (crash test dummies). Experimental Setting Three board elements including glazing (total length: 7 to 9u2005m; total height: 2.9 to 3u2005m) were mounted in the laboratory. A total of 8 systems were tested: two systems featured a standard design while 6 systems represented recent designs that claim to be more flexible. The test conditions were chosen based on previous studies. A pendulum (mass: 60u2005kg) impacted the boards at heights of 1u2005m (below handrail) and 1.4u2005m (on glazing) with velocities of 3.37u2005m/s and 4.76u2005m/s. The dummy experiments used a fully instrumented ES-2 dummy that impacted the board in a standing position (mimicking a body check position) at 4.76u2005m/s. Main Outcome Measurements The deformation of the boards was measured at 1u2005m and 1.4u2005m height. Additionally biomechanical relevant measures were recorded using the dummy. The performance of the board and the biomechanical loading of a player were assessed. Results Generally a “flexible” board design allows for more deformation than a standard design, but the performance varies strongly between different board models/ products. While standard boards deformed 13.4±3.6u2005mm and 30.7±13.1u2005mm at 1u2005m and 1.4u2005m height, respectively, “flexible” boards deformed 40.1±13.3u2005mm and 56.2±17.7u2005mm. Acrylic glazing enables more deformation than glass glazing (10–60% increase). The results were consistent for dummy and pendulum impacts. Conclusions Recent board designs exhibit a larger deformation performance compared to standard designs.

Reply to: Technical Comment on "Saccadic eye movement performance as an indicator of driving ability in elderly drivers".

With regard to the letter by Vaucher et al., it should be stressed that neither the premise of our study nor our conclusions are reflected correctly in this comment. As described in our paper, it is not intended to use solely a saccadic eye test to make a final decision on the ability to drive. However, our study indicates that such a test can be helpful as a screening tool, i.e. as a first step determinant to pre-select individuals who are likely to perform poorly as a driver and thus need a more detailed assessment. Given the high number of examinations that can be expected owing to our aging population, we believe that efficient and reliable test procedures are necessary to assess the ability to drive.