User manual

120 Appendix A: Using the EyeLink 1000 Analog and Digital Output Card

7. Appendix A: Using the EyeLink 1000 Analog and Digital

Output Card

The EyeLink 1000 eye tracking system supports analog output and digital

inputs and outputs via a DT334 card. The analog card supplies up to 8

channels of 16-bit resolution analog output, and 16 bits each of digital input

and output. The analog outputs may be used to output up to 6 channels of eye

and gaze position data for use by non-link and legacy applications. Digital

inputs may be defined as buttons, used for controlling the EyeLink tracker, or

recorded to the EDF data file. The outputs may be controlled by out-port

commands via the link, or used by the EyeLink tracker for data strobes and

other functions. A digital only card (the DT335) is also available.

This appendix describes how to configure and use the EyeLink 1000 analog and

digital outputs. While some ideas for input and control of the tracker will be

introduced, applications are not limited to those introduced here. In addition,

other digital input and output ports may be used, including the game ports and

the printer port of the EyeLink Host PC.

7.1 Analog Data Types

Position data and pupil size data are available in several types, which are

selectable through the EyeLink 1000 “Set Options” options screen. For pupil

size, either pupil area or pupil diameter may be monitored. These are very high-

resolution measurements, with a typical per-unit resolution of 5 μm (0.005

mm). Pupil size measurements are affected by eye position, due to the optics of

the eye and camera.

Position data output can be selected from one of three types of measurement:

Raw: This measurement is the raw pupil-center position (or pupil

minus corneal if running in pupil-CR mode) as measured by

the image-processing system. This measurement is available

without performing an eye-tracking calibration.

HREF:

This measurement is related to the tangent of the rotation

angle of the eye relative to the head. In the default EyeLink

1000 setup, and for the -5V to +5V output range, it is

5V*tan(angle), measured separately for vertical and horizontal

rotations. A calibration must be performed to properly obtain

this measure.