In other words, participants withheld reporting the arm that previously changed until a second change was observed. See the examples in Figures 1b and 1c below. To measure brake light detection performance as a function of fixation location and secondary task difficulty, the researchers recorded the proportion of correct brake responses, the proportion of missed brake lights, and reaction time for detecting brake lights. The results of the task were quite surprising! As shown in the figure below, brake light detection was significantly better when fixating at the center of the roadway than the right of the center and bottom center no significant difference between the center and the left.
Also, brake light detection was significantly better for the easier version of the distracting task across all fixation locations. However, there was no combined effect of fixation location and task difficulty on brake light detection a. A similar pattern of results was observed for reaction times. Participants were faster at detecting brake lights at the center fixation location than all other locations, but there was no combined effect of fixation location and task difficulty. One possibility for these results was that the secondary task did not vary enough in difficultly to detect a difference.
As a result, the researchers followed up with a second experiment where they used a more difficult secondary task. Although they found that overall brake light detection performance was better in Experiment 1 with the easier secondary task, there remained no combined effect of fixation and the more difficult secondary task in Experiment 2. Good vision is essential for safe driving. Even a small loss of vision can affect how well you read road signs or see objects from a distance.
Good peripheral vision is also very important for driving safely as many everyday driving tasks, such as merging, changing lanes and seeing pedestrians require peripheral vision. How well you see in the distance is the most important visual skill for driving. Poor distance vision becomes more dangerous as speed increases, because the faster you drive, the less time you have to react to what you see.
Information input occurs in a continuous sequence of saccadic eye movements which transport critical objects into the fovea.
After fixation, the observer analyses the object and decides whether or not a reaction is necessary. Subjects were asked to return a form indicating whether they wished to participate. They were also sent a questionnaire related to the inclusion and exclusion criteria. Exclusion criteria were severe cognitive impairments, including hemispatial neglect. All subjects scored above a predefined cutoff point 22 on the Mini-Mental State examination, 6 a cognitive screening test mean score, 27; range, Hemispatial neglect was screened by means of the Bells test 7 number of errors: mean, 1; range, Two subjects made more than 4 errors and were further tested with a line bisection task.
To gain insight into how vision parameters affect driving performance, subjects were classified into 4 groups based on the European requirements for driving.
Subjects in the peripheral field defect group group 2 met the visual acuity requirement but failed to meet the visual field requirement. Subjects in the central and peripheral field defect group group 3 met neither of the requirements. Subjects in the mild visual field defect group group 4 had scotomas in the paracentral or midperipheral area that did not restrict the binocular horizontal field extent and did not affect visual acuity.
Vision parameters for the 4 groups are presented in Table 1. Examples of the monocular visual fields of a subject with a central and peripheral visual field defect group 3 and a subject with a mild visual field defect group 4 are depicted in Figure 1. The study was approved by the ethical review committee of the University of Groningen, Groningen, the Netherlands.
Visual acuity and contrast sensitivity were assessed for each eye separately and binocularly. Visual fields were examined monocularly. The binocular horizontal field extent was obtained by superimposing the III-4 isopters of the monocular visual fields.
Viewing behavior was assessed by the attended field of view AFOV test. The target is an open circle C among 30 closed circles O. Presentation times vary from 8 milliseconds to 10 seconds.
Visual attention was assessed by a test similar to condition 6 of the usual field of view test as developed by Ball et al. The peripheral tasks involved the localization of a target, whereas the central task required the identification of central stimulus eg, a sad or happy face. Presentation times varied from 50 to milliseconds. A network specification language tool was used to develop a network of roads. A scenario specification language tool was used to define other traffic participants and their individual behavior.
Each vehicle perceived its environment, evaluated behavioral rules, and responded appropriately. The refresh rate was 20 to 30 updates per second, resulting in a smooth real-time performance with a mean response delay of less than milliseconds. On the screens, the roads, intersections, traffic lights and signs, buildings, objects, other vehicles, and 3 superimposed small rectangular areas simulating the rearview and sideview mirrors of the car were projected Figure 2 A.
Luminance was 0. Mean luminance of the cars was 1. The road consisted of 2 lanes. The right lane boundary corresponded to 0 m, the middle of the road to 3 m, and the left boundary to 6 m.
The width of the car was 1. The driving simulator car was a modified BMW on a fixed base, containing all its original controls, including steering wheel, accelerator, brake and clutch pedals, speedometer, dashboard indicators, and a manual and automatic gear shift. The engine was replaced by servomotor systems attached to the steering axle and accelerator pedal, allowing simulated torque forces while driving. Ambient sounds and engine noise were reproduced by loudspeakers.
A head tracker monitored head movements during driving Figure 2 B. Subjects were instructed to drive as they would normally and to respect all traffic signs and signals. They were allowed to practice for as long as they wished. Mean practice time was about 10 minutes. The actual driving test lasted for approximately half an hour. The rural area consisted of straight roads, roads with left curves, and roads with right curves.
The route included 14 intersections, 10 intersections without a sign and 4 intersections with a yield sign. In the first case, the driver had to give way to vehicles approaching from the right.
In the second case, the driver had to give way to vehicles that turned onto the main road, whichever side they approached from. At the start of the route, traffic density was low with a few cars approaching at intersections. Later in the route, traffic flow increased, resulting in very busy intersections at the final parts of the driving test. After 9 km, a car approached from the right. Subjects had to yield the right-of-way and were instructed to follow that car at a short but safe distance.
During the route, the subject was instructed 4 times to follow such a car. Dependent variables were speed, mean lateral position, SD of lateral position, the distance to the next intersection at which subjects started to brake, the distance to the next intersection at which the subject released the accelerator pedal, mean and minimum time-headway, minimum time to collision, viewing angle, number of head movements, distance to the next intersection at which subjects started to scan, number of times subjects overtook a vehicle, and number of crashes.
Practical fitness to drive refers to the ability of the driver to drive safely and smoothly despite a physical impairment, such as a visual field defect. It was assessed with a driving test on the road. Subjects were evaluated in their own car and their own neighborhood by an experienced driving examiner from the Dutch Central Bureau of Driving Licenses. This method of assessing practical fitness to drive is the official standard in the Netherlands for examining drivers who do not quite meet the vision requirements for driving.
Driving examiners determined whether subjects had adapted their behavior to minimize the negative effects of their impairment. Driving examiners knew about the drivers' visual acuity and visual field defects but were unaware of their performance on the driving simulator. After the driving test, the examiner gave a final score, which varied from 0 insufficient to 3 good.
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