The overall goal of this procedure is to allow an experimenter to generate an array of visual stimuli using the visual eye system to conduct an ocular-motor study. First, the visual eye system needs to be calibrated by converting pixel values to degrees using measured targets. The second step is to define the initial and final positions of the left and right eye stimuli by saving the stimuli into a library prior to the experimental session.
And finally, the eye movement monitor is placed on the subject and the experimental script is run to record eye movement responses. Ultimately, results can be obtained that show position and velocity traces of eye movements. The main advantage of this technique over existing methods, such as proprietary software, is that the operator compo any visual stimuli to conduct any types of ocular motor experiments.
Demonstrating this procedure is a doctoral student on Kim from my laboratory. Any type of eye movement monitor can be used for this system. In this demonstration, a limbus tracking and a video monitoring eye movement system will be used for tandem tracking movements such as psychotic or smooth pursuit.
A single computer can be used for the visual display to study opposing eye movements such as virgins or the interaction of virgins with tandem version movements. A haplo scope is needed with two computer monitors for visual display. First calibration is needed to convert one set of metrics into another because eye movements are typically indicated in degrees of rotation.
While computer monitors use pixel values, one can use trigonometry to calculate where to place the physical targets to calibrate the visual displays. For example, if the stimulus on the computer screen aligns with a two degree physical target, then that pixel value corresponds to a two degree stimulus. To calibrate the system, the operator needs to open the pixel to degree dot vei file within the visualize directory.
First, define the monitor to calibrate using the stretch mode field. Enter number one for the left eye monitor and number two for the right eye monitor. Then run the program and move the green line stimulus until the green line is superimposed on top of the physical target.
Now enter the known position of the physical target in degrees, and press the save button. Then click on the green line. The degree and pixel value will be shown on the display in the bottom left corner, and the operator should collect a minimum of three calibration points.
After saving all the calibration points, open the D two P Excel output file in the visualized directory. To obtain the calibration points. Plot the calibration points to attain a linear regression equation.
Use the equation to calculate the initial and final position of the visual stimulus. The operator desires to program in pixel values. An example of the left eye and right eye calibration curve obtained using five calibration points for a virgin stimulus is shown here.
Repeat the previous two steps for the other monitor if the stimulus requires an additional monitor. First, the operator needs to define the initial and final position of the left and right eye stimulus prior to the experiment. To do this, open a new text file and on the first row, define the initial time and position values.
Four parameters need to be defined, the time, the horizontal position, the vertical position, and the rotation each separated by a tab. Likewise define the four final parameters, the final time, horizontal position, vertical position, and the rotation of the stimulus. Save the stimulus in the visualized directory as a stimulus name dot vii file, and repeat this step for any other I stimulus.
Next, the movement of the stimulus can be generalized into two types of movement. An abrupt step or a continuous ramp. A step allows the stimulus to abruptly move or jump from the initial position to the final position.
The operator should note that the change in time should be 0.001 seconds for a step stimulus. An example of a psychotic step, smooth pursuit ramp, virgin step and virgin ramp are shown in table one. For stimuli, you can have a single stimulus, such as a step or a sequence of visual tasks, such as a multi-steps.
Now, save both stimulus files in the stimuli library. Note that there are several default settings within the visualized directory. The first line is the percentage of the screen within the horizontal direction.
The second line is the percentage of the screen within the vertical direction. The third is the background image, and the fourth is the foreground or target image. The fifth line indicates that the computer should work in independent mode.
The sixth line signifies which monitor is used. The seventh line is the aspect ratio of the monitors. The rest of the lines are the different types of stimuli the operator can use within an experimental session.
Now, open the left eye stimulus monitor and the right eye stimulus. Monitor files from the visualized directory. These two files contain the library stimuli for the left eye and the right eye respectively.
On the last row, write the file name of the stimulus that has been defined. The profile number refers to the row corresponding to the stimulus file name. For example, here the profile number of the stimulus is eight.
One can repeat the previous steps to create as many stimuli as are needed for an experiment. Next, the script for the experimental protocol can be written. First, open a text file to type the experimental protocol commands and save this file in the visualized directory as a script name vs file.
This will be the script file from which the visualize system will read and execute commands. The visualized functions have input and output arguments. This table displays all the functions in the visualized software that can be used when the temp file dot lwf is not defined.
During the execution of this function, the software will not store any incoming data for digitalization. The log file function output strings, or the input buffer defined from the EXP trial into the out text file in the visualized directory. When the experiment is complete, be sure to change the name of the out text file to another name.
Otherwise, the data will be overwritten during the next experiment. The trigger weight function waits for the subject to push the trigger button to start the experimental trial denoted as exp trial on the screen and digitize the data. This is channel 12 on the digital acquisition card that it's waiting for the signal to change from a digital high to low.
Finally, the random delay function generates a random delay to prevent prediction or anticipation of the next stimulus, and the wave MSD function calculates the mean and standard deviation of the data. Before beginning an experiment, the subject must provide written and informed consent approved by the institutional review board. The experiment must be explained in detail before a subject can agree to participate.
Different eye movement monitors, such as the corneal reflection video imaging system, limbus tracking system, or sclera search coil may be used to collect and record eye movements. Here we will demonstrate a limbus tracking system. Then adjust the eye movement monitor to capture the anatomical attributes of the eye, such as the limbus or the pupil and corneal reflection, depending on the eye movement monitor used.
Once the eye movement monitor is properly adjusted on the subject, validate that the eye movement monitor is capturing the eye movements by asking the subject to make side to side psychotic or inward and outward called virgin movements. Open the program Read script dot vei in the visualized directory on the upper right corner, type the file name of the experimental protocol script file created previously. Then run the read script dot vei program by pushing the arrow button on the top left corner.
Next, give the subject the trigger button and explain that when the button is pushed, data collection will begin. Another acquire VEI file will automatically appear on the screen, which will plot the incoming data. Data are sampled at 500 hertz.
When the experiment is complete, the read script dot bei will automatically stop at this time. Go into the visualized directory and find the out text file. Rename the file.
Otherwise, the next time the operator runs the experiment, the data file will be overwritten. When the experiment is complete, the data can be analyzed using different software packages including MATLAB or Excel latency. Peak velocity or amplitude may be of interest depending on the study.
An example of a MATLAB analysis code is provided in the visualized directory to plot SEC codes, virgin steps, and virgins ramps. Here we see examples of the ensemble of eye movements that can be recorded using the visualized system. In these plots, we see typical 10 degrees psychotic movements, also called Proseccos.
Our research uses degree of rotation. Eye movements can be calibrated in units of degrees, meter angles, or prism diopters. Each trace represents an individual eye movement where in the upper graph position is denoted in degrees as a function of time.
The bottom graph is the velocity plotted in degrees per second as a function of time. Antis cos are shown here. These are psychotic responses.
When the subject is told to make a secod in the opposite direction of the visual stimulus, virgin's responses to four degrees. Steps can be seen here and virgin's responses to five degree per second ramp stimuli are shown here. While attempting this procedure, it is important to remember to calibrate the system prior to the subject coming in for a study.
Give proper instructions to the subject and ensure the eye movement monitor is correctly adjusted for the subject. After watching this video, you should have a good understanding of how to program using the visualized scripting language to construct your own visual stimuli to study a broad range of ocular motor experiments. Ocular motor research benefits from a strong research foundation because it can yield insight into the normal and dysfunctional brain.
