I use a National Instruments analog to digital data acquisition card. It has a shielded cable that connects to an input box which has several BNC direct DC inputs, organized into a series of channels with X and Y inputs for each channel. My box can take as many as 16 single inputs, 8 dual inputs, or 8 bias differential referenced channels.

Matlab has an optional toolbox called the Data Acquisition Toolbox that's specifically made to interface with and control various types of DAQ cards. I use this toolbox to sample the eye tracker's output while I'm displaying stimuli to subjects using a run time toolbox called the Psychophysics Toolbox. My using Matlab's ability to run complex programs, I'm able to build commands from both of these toolboxes that give me a run time environment which controls my experiments and collects my data.

The eye tracker we have is linked to an oculometer; a controller box that allows me to set the power and sensitivity options of the eye tracker, as well, as the range of voltages the X - Y channels put out in term of their gain and zero bias. I have the output calibrated to a set of values and ranges for voltage through the DAQ Toolbox in Matlab. My program includes commands to start and stop recording from the eye tracker at the beginning and end of the stimulus presentation, while subjects are looking around the screen.

What I get is a list of X - Y coordinate pairs, in terms of the voltage level output by that channel at that point in time. I sample at 250 times a second. I can then take these coordinates, and plot the path that a subject's eyes took while scanning the display.

So, this is how I use it and what I do with it as an instrumentation control system. I don't output commands to control external devices, with my system, but that capability is integral to the system if you have a DAQ card that's also capable of issuing outgoing commands.