User manual

58 An EyeLink 1000 Tutorial: Running an Experiment

8) Place one of the EyeLink Remote target stickers on the subject’s forehead

(see Figure 3-12), just above the eyebrow of the tracked eye so that both

the eye and the sticker stay within the camera image when the subject’s

head moves throughout the expected range. If the target sticker is placed

too low on the forehead (see middle panel of Figure 3-12), a red

horizontal bar will be displayed in the global view of the camera image

(on the Camera Setup screen) and an EYEDIST error will appear on the

status panel (on Offline, Calibrate, Validate, Drift Correct, Output and

Record screens). If the target sticker is placed too far toward the temple

(see bottom panel of Figure 3-12), the tracker may report an ANGLE error

in the status panel when the subject moves too far in the direction of the

sticker.

9) One other potential problem concerns occlusion of the pupil image by the

nose when the subject’s head is rotated. If this presents a problem

because the majority of a stimulus involves the subject looking to the

side of space where the illuminator resides (opposite the camera),

consider tracking the eye on the same side of space as the camera. One

side of space will still afford a relatively more restricted view due to

occlusion of the eye by the nose, but now the restricted range of looking

will be on the same side of space as the camera. For example, when

tracking the left eye, a greater range is available when the subject is

looking to the right, because when the subject looks far to the left, the

nose will occlude the camera’s view of the left eye.

10) For optimal performance, adjust the subject’s seating distance so that

the tracker reports a target-camera distance of about 550 mm to 600 mm

in the zoomed target view (bottom right camera image). If subject is

seated too close to the camera, the Host PC will display a “DIST CLOSE”

error. If the subject is seated too far from the camera, the tracker will

report a “DIST FAR” error. If the tracked eye does not appear centered in

the global camera view, the angle of the Desktop Mount may be rotated

slightly.

11) The camera image is now ready for fine tuning adjustments and

establishing of threshold biases. In the global view window of the camera

image (Host or Display PC), select the tracked pupil using the mouse

cursor, and click the left mouse button. If the camera image is not

focused, rotate the focusing arm and look closely at the eye image on the

zoomed view. The best focus will minimize the size of the yellow corneal

reflection circle.

12) If the pupil is detected, a green box and crosshairs will now be drawn on

the eye image in the global view. In the zoomed view, the pupil area is