>Psychtoolbox>PsychHardware>EyelinkToolbox>EyelinkTests

EyelinkGetTrackerImageDemo([sndinit = 0])
This shows you how to register a callback m-file that can display the
tracker’s eye image in PTB.

sndinit = 0: No sound init / legacy behavior.
1: EyelinkUpdateDefaults for default init.
2: Pass in our own PsychPortAudio sound handle for optimal method.