View source for EyeLink

=Powering up and starting EyeLink=
Find the top battery, check whether the battery is sufficiently charged (press test button), and bring it into the MR system room. Plug in the two power cables and turn the battery on. The EyeLink software will give an error message during start-up if the battery is not connected and turned on. After placing the battery, remove the lens cap from the EyeLink camera. Don’t forget to turn on the BOLD screen.

Turn on the EyeLink monitor and select DVI as input (by default it is on Display Port, which is for the stimulus computer). Then turn on the EyeLink computer and choose EyeLink mode. You should now see the EyeLink graphical user interface (GUI).

Also turn on the stimulus computer and start up the Track software from the desktop shortcut. Keep the standard EDF filename (SDEMO), and hit enter twice so that the camera image is visible on the BOLD screen. Make sure that you are viewing the overview (zoomed-out) image by pressing the arrow-keys on the stimulus computer.

Important: the EyeLink setup does not return to defaults after shutting down the EyeLink. Make sure that all settings are correct before starting your experiment. For some default settings, see [[EyeLink#EyeLink_Settings | EyeLink Settings]]

=Participant preparation and placement=
Prepare the participant by removing mascara and replacing glasses for MRI glasses. Soft contact lenses can be worn during an eye tracking experiment, but rigid contact lenses may interfere with the corneal reflection (CR) and thus need to be switched for MRI glasses.

When the participant is placed inside the scanner, make sure that the eyes and eyebrows of the participant are not covered by the head coil, as the head coil may cast a shadow over the eyes and that interferes with the experiment. When you slide the participant in the scanner make sure you align on the eyebrows (to make sure every participant is more or less in the same position).  Don’t forget to exchange the regular mirror (grey backside) for the first surface mirror (mirroring backside). Important: do not touch the first surface mirror with your bare hands, as this irreversibly damages the mirror.

After the participant is placed in the bore and the camera is setup correctly, look past the camera to see if the participant’s eyes are in the centre of the mirror. If this is not the case, adjust the mirror. Ask the participants if he or she can see all corners of the screen. Under normal circumstances, the EyeLink camera and illuminator have already been set up correctly and you should see the participant’s eye in approximately the centre of the overview image, after which you can move on to step 3. If the eye is not (properly) visible or illuminated, first check whether the feet of the BOLD screen tripod are on the marked locations. If they are and the eye is still not in the image, please contact the staff of the Spinoza Centre so that they may realign the EyeLink camera and illuminator.

=Focus and adjust=
Make sure that the ‘threshold coloring’ option is turned on. Click on the pupil on the EyeLink computer and switch to the zoomed-in view on the stimulus computer by pressing the arrow-keys. Carefully adjust the focus of the camera so that the size of the CR becomes as small as possible. This means that the pupil is in focus. Press A (or auto threshold) on the EyeLink computer to adjust the thresholds, and inspect the values under the image. The entire pupil should be coloured dark blue, and the pupil value (P) should be above 70. The CR value should be as small as possible. If too much light enters the pupil, part of the pupil may not be dark blue anymore, and you will see question marks behind the P value. If this is the case, adjust the lens of the illuminator slightly (see [[EyeLink#Adjusting the illuminator | 7.2]]). A red P or CR value means the software cannot determine the position of the pupil and/or CR, which may often be solved by adjusting the position of the mirror. Another cause may be that the participant is wearing mascara. If neither are the case, the illuminator alignment needs to be adjusted. If you are unsure how to do this, please contact the staff of the Spinoza Centre.

=Calibrate and validate=
Set the desired calibration and validation settings. It is recommended to perform calibration in randomized order. Instruct the participant to focus on the centre of the calibration points and not to change their gaze until the calibration point disappears. Note that even when you’re not doing an eye tracking experiment, but are only monitoring pupil size, it is still recommended to do at least a three-point calibration.
 
===Calibrate===
Start calibration by pressing the C button or clicking the calibrate button. The first calibration point needs to be manually accepted by the researcher by pressing the spacebar. On the screen you will see a small green triangle, which moves if the participant moves their eyes. Wait for the triangle to be completely still and then press the spacebar to start calibration. Whenever the participants gaze reaches a calibration point, a green cross will appear on the EyeLink image. For a 9-point calibration you want these crosses to form a perfect grid. Either accept the calibration by pressing enter or clicking accept, or move on to validation.

===Validate===
After calibrating, start validation by pressing V or clicking the validate button. The first validation point needs to be manually accepted by the researcher by pressing the spacebar. Every time the participant’s gaze reaches a validation point, a value (degrees of deviation) appears on screen. You want these values to all be below 1; if this is not the case, recalibrate.

=Shutting down=
Quit the Track software on the stimulus computer by repeatedly hitting the escape button. Quit the EyeLink software by clicking ‘Exit EyeLink’ which returns you to MS-DOS, after which you can turn of the EyeLink computer by pressing the power button. 

Put the lens cap back on the EyeLink camera, turn off and unplug the battery, place it under the fully charged battery and plug it in to charge. Switch the EyeLink monitor back to Display Port so that other users can use the monitor for the stimulus computer.

=EyeLink Settings=
For a full overview of possible EyeLink settings, please refer to the EyeLink 1000 manual, which may be found on the leftmost red shelve. The settings discussed here are settings that should generally not be adjusted.

===Camera setup===
* Sample rate should only exceed 250 Hz for microsaccade experiments; increasing the sample rate may increase noise;
* Eye should be set to left;
* Image Display: ellipse;
* Crosshairs: on;
* Threshold coloring: on.

===Set Options===
* Pacing interval is the interval between calibration stimuli. This should be at 1000 (ms). Randomize order and repeat first point should also be turned on;
* Configuration should be set to Long Range Mount.


=Realigning the EyeLink camera and illuminator=
Alignment of the EyeLink camera and illuminator should only be performed by experienced EyeLink user or the Spinoza Centre staff.

===Adjusting the camera===
The EyeLink camera and illuminator are attached to a mounting-bar, which is held in position by a bolt under the BOLD screen. Loosen the bolt and adjust the camera so that the eye and pupil of the left eye are in the middle of the image and fasten the bolt tightly; adjusting the camera is the easiest when looking past the camera. Make sure that the bar is horizontal, as this makes it more likely that the illuminator is correctly oriented. Important: be very careful not to move the screen while orienting the camera.

===Adjusting the illuminator===
Return to the EyeLink computer and click on the pupil. Make sure that the image on the BOLD screen is the overview image, as this makes it easier to see the position of the illuminator beam. If the ‘threshold colouring’ option is turned on, dark areas should be coloured dark blue and overexposed areas should be coloured cyan. In the ideal situation only the pupil is dark, and all other areas are not. It’s better to overexpose than to underexpose. The exposure can be altered by adjusting the illuminator: 
* First adjust in vertical direction by loosening the bolt on the bar;
* Next adjust in horizontal direction by loosening the single bolt closer to the lens. Make sure to support the illuminator, else it might bend down;
* Last adjust the lens so that the beam becomes more focussed. Usually it needs to be extended quite far.

As a check you can ask the participant whether he or she can see all lights in the illuminator.

=Hotkeys=
* ENTER - show eye on monitor 
* Left/Right – switch between zoomed in/zoomed out image
* C - calibration 
* SPACE - start calibration 
* ENTER - accept calibration 
* V - validation 
* SPACE - start validation 
* ENTER - accept validation 
* Within Presentation (stimulus computer):
* F4 ->either back to eye screen, or start of experiment 
* ENTER -> accept drift check (when you see fixation point in center of screen)
* F4 -> start experiment
* D - Drift check (correct for eye movement on one central fixation point)
* Enter - accept drift correction

=Abbreviations=
* CR - Corneal Reflex
* GUI - Graphical User Interface
* P - Pupil value