User manual

60 An EyeLink 1000 Tutorial: Running an Experiment

15) The operator can easily tell if the pupil has been detected because the

image on the Host PC will have a crosshairs indicating its center. A green

ellipse, updated each refresh, is drawn around the elliptical pupil fitting

algorithms (see section 3.6 “Pupil Tracking Algorithm”). If a shadow

interferes with pupil detection, or if the eye image is clipped by the side

of the camera window, the crosshair and ellipse fitting will disappear and

the pupil will be lost. On the Host PC, a red warning message will appear

below the small camera image for the eye indicating “No Pupil”.

16) The EyeLink Remote exclusively uses Pupil-CR mode. The CR, if present,

is identified by a yellow-filled, white circle marked by a crosshair. The CR

threshold value and bias are displayed under the zoomed camera view.

The CR threshold is updated automatically and CR biases can be

manually adjusted using buttons, or the + and – keys. Heuristically, CR

biases should range from 0.9 to 1.1 (a value around 1.0 is

recommended). Once the threshold bias is adjusted, 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.

17) By default, the “Illuminator Power” level of the EyeLink Remote is set to

100%. If the Desktop Mount is placed too close to the participant or if the

CR signal is not reliably acquired, you may consider lowering the

illumination level to 75%. One sign that illumination may be set too high

is excessive yellow coloring of the face.

18) The EyeLink Remote draws a red search limit box that is automatically

updated with changes in pupil position. This search limit area is used to

exclude regions of the camera image (e.g., frame of the glasses, eye brow)

that may otherwise be detected as a pupil/CR reflection pattern. If the

search limit box isn’t aligned on top of the pupil, press “A” or the “Align

Eye Window” button to center it. The size and shape of the search limit

area can be adjusted by pressing ALT and cursor keys on the host

keyboard together (ALT + ⇑ or ⇓ to adjust the height; ALT + ⇐ and ⇒ to

adjust the width). The position of the search limits can be adjusted with

SHIFT and cursor keys.

19) The operation of the EyeLink Remote is influenced by ambient lighting.

In general, the pupil shrinks in a bright environment and dilates with

dim lighting. It’s important that the user check the pupil size reported in

the status panel (in the Offline, Calibrate, Validate, Drift Correct, Output

and Record screens; see Figure 3-14). If a yellow size warning is

constantly observed, it is likely that the pupil size is too small and as a