>Psychtoolbox>PsychHardware>EyelinkToolbox>EyelinkDemos>SR-ResearchDemos>GazeContingent>GCFastSamples

A simple EyeLink gaze-contingent demo showing how to retrieve fast online samples.
In each trial an image is presented with a red gaze-contingent dot overlaid on top.
The dot’s location is updated online based on the x y coordinates of the latest gaze sample retrieved online.
Each trial ends when the space bar is pressed.

Usage:
Eyelink_GCfastSamples(screenNumber)

screenNumber is an optional parameter which can be used to pass a specific value to PsychImaging(‘OpenWindow’, …)
If screenNumber is not specified, or if isempty(screenNumber) then the default:
screenNumber = max(Screen(‘Screens’));
will be used.

The demo checks if a new sample is available online via the link. This is the most recent sample, which is faster than buffered data.
This is equivalent to eyeLink_newest_float_sample() in C API. See EyeLink Programmers Guide manual > Function Lists > Message and Command Sending/Receiving > Functions
It allows access to the following sample properties:

  time (sample time)  
  type (SAMPLE=200)  
  gx ([left gaze x, right gaze x])  
  gy ([left gaze y, right gaze y])  
  pa ([lef eye pupil size, right eye pupil size])  
  rx (x 'pixel per degree' value)  
  ry (y 'pixel per degree' value)  
  buttons (button state and changes)  
  hdata (contains a list of 8 fields. Only the first 4 values are important:  
        [uncalibrated target sticker x, uncalibrated target sticker y, target sticker distance in mm, target flags)