User manual

68 An EyeLink 1000 Tutorial: Running an Experiment

Follow the following steps to acquire the best CR:

a) Press the Auto Threshold button to set the CR threshold. You should see

a yellow circle appear near the pupil on each eye. Auto Threshold should

almost always set the correct CR threshold.

b) If the auto thresholding sets the threshold too low or high, use the CR

threshold buttons, or the + and – keys, to manually adjust the CR

threshold.

c) Have the subject slowly look along the edges of the display surface and

ensure that the corneal reflection does not get lost. If the CR does get

lost, a red warning message will appear below the small camera image for

the eye indicating “No CR” on the Host PC.

NOTE: Corneal reflection will not be stable with all subjects, particularly those

wearing glasses with a heavy anti-reflection coating when using the Tower

Mount. If, after ensuring the Tower Mount IR mirror/Desktop Mount optics is

positioned correctly, subject properly seated, and thresholding has been

performed, you are unable to acquire a stable corneal reflection, it is suggested

that you do not use subject for the experiment. Unlike the EyeLink II, don’t

attempt to switch to pupil-only mode for tracking of the subject without using

the bite bar.

3.5 Search Limits

The EyeLink 1000 eye tracker also provides a “Use Search Limits” option. If

enabled, it draws a red box or ellipse in the global view of the camera image and

reduces the area of the full camera image that is searched to find the eye. If the

subject does not wear glasses, you may uncheck the “Use search limits” button

on the Camera Setup screen. This allows the tracker to search for pupil position

across the whole camera image in case the pupil position is lost. The “Use

Search Limits” button should be checked for participants wearing glasses. This

can be used to exclude other regions of the camera image (e.g., frame of the

glasses) that may otherwise be detected as a pupil/CR reflection pattern. The

disadvantage of using the search limits, however, is that if the participant

completely removes their head from the head support and then puts it back in

the head support device the search limits box may not be in the correct location

to track the eye. This is especially the case when the “Move Limits” button on

the Set Options screen is checked.

The size of the search limited for the selected eye can be adjusted by pressing

ALT and cursor keys on the host keyboard together (ALT + ⇑ or ⇓ to adjust the