User manual

70 An EyeLink 1000 Tutorial: Running an Experiment

• Randomize target order: YES

• Auto-trigger pacing: 1000 msec

Press the “Previous Screen” button when done to return to Camera Setup.

Begin calibration by pressing the ‘Calibrate’ button from the Camera Setup

menu. A calibration target will appear on both the Host PC display and the

Display PC monitor. The subject display is drawn by the TRACK.EXE

application, in response to commands from the EyeLink tracker. The Host PC

screen will also display the raw pupil position as a moving colored circle, and a

thresholded image. A status bar at the bottom-right of the display reports the

progress of the calibration.

The pupil-position cursor will jump about when the subject looks about on the

display, and becomes still when properly fixating the calibration target.

Instructing the subject to carefully look at the white spot in the middle of the

black calibration target will help improve fixation stability. Head movements

during calibration should be discouraged: small head movements are corrected,

but large movements will severely degrade calibration accuracy, due to

distortion of the calibration data pattern and range.

If the cursor jumps continuously and rapidly, or disappears intermittently, the

setup for the eye has problems. The eye-movement condition is also visible at

the right side of the status bar at the bottom of the Host PC's display.

When the pupil appears stable to accept the first fixation, press the ‘Accept

Fixation” button or the ↵ (ENTER) key or spacebar key. The pupil tends to come

to rest gradually and to make small vergence movements at the start of the

fixation, so do not respond too quickly. However, do not wait too long before

accepting the fixation, as subjects soon begin to make involuntary saccades.

The proper timing is best learned by watching the gaze cursor during validation

(discussed later).

The EyeLink system helps prevent improper triggering by locking out the ↵ key

if the eye is moving. Sometimes the ↵ key will be locked out because of poor

camera setup, with the pupil noisy or undetected in some positions. You can

use the ⇑ and ⇓ keys to change the threshold if required. If this fails, press the

‘ESC’ key to exit back to the Camera Setup menu.

After the first fixation has been accepted, several more calibration targets are

displayed in sequence and fixations for collected each. The EyeLink calibration

system presents these targets in a random order, which discourages subjects

from making saccades away from the current target before it disappears.