Now Shipping! – The EyeLink 3; combined head and eye tracking at up to 1000 Hz.

SR Support Forum   ›   Learning Resources   ›   FAQs   ›   EyeLink Hardware FAQs   ›   FAQ: What is the analog card, and how / why should I use it?
FAQ: What is the analog card, and how / why should I use it?
Sam
Research Support Specialist
*******
Joined: Aug 2020
Posts: 1,015

#1
09-09-2020, 02:42 PM
The EyeLink analog output card converts the digital eye-tracking signal into an analog voltage, which can be recorded by an external acquisition device. This feature is typically used when other analog physiological data (e.g., MEG, EEG, EMG) are being collected concurrently with eye movements. By sending the eye-tracking data in the same analog format as the other recordings, it can simplify synchronization and analysis for some systems, but may have consequences on the quality of the analog data depending on your setup and analog acquisition device.

Analog Output Capabilities:
  • Analog Gaze Position: The EyeLink analog output card provides six separate channels for the X and Y gaze position and pupil size for each eye.
    Data Type: Only raw gaze data (X/Y position and pupil size) are available in analog output format. The parsed gaze data (fixations, saccades, blinks, etc.) are not available through the analog output but are still recorded in the EDF file.
  • Synchronization: A strobe signal, which is locked to the eye tracker's sampling rate, is also available for precise data synchronization.
  • Digital I/O Capabilities: The EyeLink analog output card can also be used to send and receive digital input and output triggers (TTL).
    For detailed instructions on setting up the card for TTL triggers, please refer to Section 7.4, "Digital Inputs and Outputs." Figure 7-1 in the manual provides the pin mappings for these channels for your particular hardware.
Important Note: The analog signal can be susceptible to electromagnetic (EM) interference from other devices. Therefore, care should be taken to ensure that the cabling from the Host PC to the analog acquisition device is properly shielded.

Configuration and Channel Mapping:
The specific channels used for data output will vary based on the settings in the ANALOG.INI file and the eye(s) being tracked. The table below illustrates the full matrix of possible data output assignments based on the tracking mode and ANALOG.INI settings.
   

For comprehensive information on using the analog and digital output card, please consult Section 7, "Appendix A: Using the EyeLink 1000 Plus Analog and Digital Output Card," in the relevant user manual: