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Eye-Tracking Control to Assess Cognitive Functions in Patients with Amyotrophic Lateral Sclerosis
Chapters
Summary October 13th, 2016
Cognitive deficits are common in about one third of patients with amyotrophic lateral sclerosis, a neurological condition leading to progressive impairments in speech and movement abilities. To conduct cognitive tests in patients unable to speak or write a reliable and easy to administer eye-tracking paradigm was developed.
Transcript
The overall goal of this eye-tracking paradigm is to use an oculomotor based technique to assess cognitive functions in patients with Amyotrophic Lateral Sclerosis or ALS who are unable to speak and write. This method can help answer key questions in the field of potential cognitive deficits in patients with severe physical impairments, such as ALS. The main advantage of this technique is that it uses eye movement to conduct neuropsychological testing in ALS patients, and therefore is suited for patients who are unable to speak or write.
Though this method was developed for patients with ALS it can also be applied to other patient samples unable to speak and write but within intact oculomotor control. For this experiment, use a portable eye movement recording device with goggles. Optimize eye movement detection by adjusting the cameras in all six degrees of freedom.
Next, set up a standardized oculomotor testing paradigm such as a series of saccadic tasks in order to detect deficits in eye movement control. Use software to present these tasks on a hemicylindrical screen via a projector that is mounted above where the participant will sit. Finally, in preparation for the second part of the experiment, check that a red laser spot, which will be used for the eye-tracking based version of the D2 test, appears correctly on the screen.
Begin by asking the participant to turn off all potentially disturbing devices, such as mobile phones or pagers. Bring a participant who does not have substantial visual impairments into the testing room. Seat them on an elevated chair in front of an adjustable chin rest that is 150 centimeters from the computer screen.
Ask the participant to place their head on the chin rest. And then place the video-oculography goggles on their head. Adjust the goggles to properly fit the head shape and size.
Ensure that both eyes are visible on the experimenter's screen, and focus the cameras within the goggles so that the images of each eye are centered on the screen. Next, check that the system is continuously recording eye movements at all times by instructing the participant to look in each corner of the hemicylindrical screen. Start the standardized oculomotor testing paradigm and have the participant complete a second calibration.
Ask the participant to track a single spot on the screen oscillating horizontally and then vertically with a frequency of 0.125 hertz in order to map the non-calibrated orthogonalized raw data from the eye movement recording device with respect to the true orthoganlized eye position. Finally, check if the calibration is acceptable, meaning the true eye movement and the raw data are spatially and temporally synchronized. If so, instruct the participant to keep their head as still as possible.
For the first part of the experiment the Raven's colored progressive matrices, or CPM test, displays a series of matrices 22 degrees long and 15 degrees high on the screen with a blank space cut out. Instruct the participant to identify the missing piece below each matrix. After making a choice, have the subject close their eyes for at least 250 milliseconds to start off a green frame outlining the six possible alternatives of missing pieces for 1500 milliseconds each.
Ask the participant to designate the alternative they think is correct by closing their eyes for at least 250 milliseconds while their choice is within the green frame. Project the participant's choice separately on the hemicylindrical screen, in order to confirm, instruct them to close their eyes again for at least 250 milliseconds. Have the participant complete further training by selecting the missing piece in the next three matrices.
Answer any questions the participant may have about the procedure. Then have the participant complete the full CPM task. For the second part of the experiment, the D2 test, ask the participant to direct their gaze to the center of the screen.
Tell them to observe each of the 47 letters with a height of 11 degrees and a width of 2.5 degrees, one after the other in the middle of the screen in which each stimulus lasts for 2000 milliseconds. Whenever the letter d with two dashes is presented instruct the participant to look at the red laser spot positioned above the letter until the next stimulus appears. Finally, after the training is complete, have the participant complete the full D2 test, consisting of five blocks of 47 stimuli each.
In a sample of patients with Amyotrophic Lateral Sclerosis, or ALS, there was a good congruency between the eye-tracking and standard version of the CPM test. Furthermore, there's significant group differences in the CPM test and the D2 test, indicating that this technique reliably distinguishes between more and less cognitively impaired ALS patients. Once mastered this technique can be completed in 25 minutes if it is performed properly.
For ALS patients with insufficient oculomotor control other methods, such as the brain-computer interface can be utilized in order to assess their cognitive functioning. After watching this video, you should have good understanding of how to perform eye movement based neural psychological testing with ALS patients.
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