The overall goal of the following experiment is to differentiate compensatory strategies of visual exploration in patients with visual field defects after infarction of the posterior cerebral artery. This is achieved by positioning and instructing patients in a driving simulator in order to examine behaviors in a realistic test situation. A head mounted eye tracking camera is used with accuracy insured by making adjustments and calibrating for the individual patient.
Next, the driving simulation begins while gaze behavior and driving performance are recorded as an alternative mode, the overlay pictures can be turned on in order to visualize and allow for a quick assessment of compensatory gaze behavior. Different strategies are revealed by the evaluation of secod and head movement parameters, such as the number of secs, sec amplitudes, fixation, distribution, and duration, as well as reaction times to peripheral objects. The main advantage of this simulated driving setup is that it allows for fast and easy assessment of visual exploratory behavior within a clinical setting.
Now we can record well defined parameters such as eye and head movements and reaction times. The implications of this technique extend to what rehabilitation and therapy since immediate visualization of gaze behavior via the overlay control may provide a feedback mechanism to raise the patient's attention and assist with learning compensatory strategies. It may also improve efficiency of rehabilitation by offering more individualistic rehabilitation plans adjusted to the patient's current level of compensatory behavior.
My colleague bur our doctoral candidate from our laboratory, will demonstrate the procedure To begin this protocol. First, have the patient take a seat two meters in front of the simulation screen in an imitation car seat, help the patient adjust the back rest as well as the seat distance to the pedal. Once the patient is comfortably positioned, provide instructions on using the simulation car, including the brakes, the turn signal, and the steering wheel.
Then provide task instructions. Instruct the patient that just as in a real driving situation, the brake and or turn signal should be used as appropriate and the respective driving situation. Also, be sure to inform the patient about simulation sickness and let the patient know that the testing session can be interrupted in the case that malaise, nausea or sweating occurs.
Next, conduct a test drive with low task density to allow the patient to get used to the simulation car and stimuli. This may also prevent simulation sickness by providing time to adjust to the simulator in a second testing session. After the patient is properly seated and has received enough time for practice, place the eye tracker on the patient's head and adjust it to fit by pulling the flexible straps to prepare software and patient for calibration.
The head camera laser should be pointing to the middle of the simulation screen and the cameras adjusted to focus on the pupil. Then instruct the patient to sequentially look at five dots on the screen by following the lead of the mouse arrow and begin calibration of the eye tracking equipment. Next, complete the horizontal calibration.
Instruct the patient to fixate on an overlay picture of an eye on the left screen. Then follow the overlay moving across the screen and fixate on it again on the right side. Test the calibration by asking the patient to fixate on specific objects on the screen and then match this fixation with an overlay eye picture, which indicates the gaze position calculated by the software.
The calibration is successful if the patient's gaze and the overlay picture meet at the same spot on screen. Repeat calibration if needed. Once calibration is complete, turn off the overlay pictures.
Once the patient is comfortable in the simulator and the eye tracker has been successfully calibrated, proceed with the simulation. In this example, the patient is driving on a one-way single lane road with obstacles. The patient should react as quickly as possible to moving objects approaching the road such as wild bore or balls, but also to street signs or broken down cars appearing on either side of the road.
Note that while pressing the accelerator, the car can speed up to a constant speed of 70 kilometers per hour unless the break is used. Let the patient drive on several different routes, each of 6, 500 meters and approximately 10 minutes duration with different task difficulty due to level of distraction by surrounding environment. As an alternative testing mode, turn on overlay eye pictures, one indicating the gaze position while the other one indicating the head position of the patient.
This allows a quick assessment of compensatory behavior of gaze movements simultaneously to testing by visualizing the gaze position through the software. Here we can see a typical driving performance of a patient with Hemi Opia On the right side with compensatory gaze behavior. Gaze behavior is visualized by the overlay eye pictures, which allow a quick assessment of head and eye movement position compensatory psychotic movement to the side where the visual defect is located is exhibited, resulting in detection of objects appearing in the blind field.
Note the exemplary performance of the patient with Hemi Opia on the right side, and here we can see typical driving performance with visualized gaze behavior of a patient with hemianopia on the right side without compensatory behavior causing collisions with objects appearing in the blind field. Note the exemplary performance of the patient with hemianopia on the right side without compensation. MATLAB software can be used to analyze the experimental data recorded from the simulation.
Define secs as sections of the gaze trajectory where gaze velocity exceeded 30 degrees per second and gaze amplitude was larger than one degree. Sections between secs should be defined as fixations and head movements defined as movements exceeding six degrees per second and amplitude of more than three degrees. Slab software can be used during the experiment to record speed reaction times when using the turn signal and break and lane position object fixations should be defined as fixations on an object with gaze position maximal to 1.24 degrees apart from the object on the x axis and 1.66 degrees on the Y axis seen.
Here are results for two patients with incomplete hemianopia on the right side, driving with and without compensatory behavior patient A exhibited compensatory psychotic movement to the side where the visual defect is located resulting in normal performance in driving simulation compared to a healthy control. However, patient B did not show compensatory psychotic movement and revealed poor performance in driving simulation by missing peripheral in the blind field, causing prolonged reaction times or collisions. Here we see the distribution of fixations on the screen during the first drive of patient A, patient B and a healthy subject patient, A exhibited compensatory psychotic movement to the side where the visual defect is located while patient B explored less.
Patient B performed 3.4 times fewer psychotic movements compared to patient A covering half the size of the amplitude of patient A.Patient B also showed longer fixation durations compared to both healthy control and patient A.This figure demonstrates the influence of eccentricity of object position with respect to GA's position on the reaction time demonstrated separately for the left and right side of the visual field. For patient A and the healthy control, there was no significant difference between reaction times to approaching objects by manual detection or fixation of the object to the left or right field of vision. In patient B, however, reaction times differed clearly between the blind and the sighted field.
While attempting this procedure, the patient needs to be informed that fitness to drive cannot be concluded from this experiment to clarify whether compensatory behavior breaks down when transferred from a safe simulated situation to an actual driving situation. Real driving studies need to be performed. This stimulation can be completed within 10 minutes performed properly.
It can give a first impression of the visual exploratory behavior, and after watching this video, you will have a good understanding of how this technique quickly and conveniently uncovers visual exploratory behavior in a naturalistic situation.
