Getting Started: Getting Started with Biosemi Integration
Connecting up the Equipment

The integration between a Biosemi EEG device and an EyeLink tracker is fairly straightforward, as Biosemi can only receive event markers via parallel communication. As shown in the diagram below, you can use one of the following solutions.
  • Option #1: TTLs through the parallel port. Using a Y-shaped split cable to connect the parallel port on the Display PC directly to the BioSemi USB receiver and the EyeLink tracker. So, the same TTL signals are received by both the BioSemi EEG device and the EyeLink tracker.

  • Option #2: TTLs through the parallel port (to BiosSemi USB receiver) & messages to the EyeLink Host PC via Ethernet. This is one population, which eliminated the additional Y-shaped splitting cable required for Option #1. When a critical trial event occurs, you send a message to the tracker via the Ethernet connection between the Display PC and the EyeLink Host PC. Immediately following this message, send a TTL via the parallel port to the BioSemi USB receiver. You can use the messages and their corresponding TTLs to synchronize the EEG and eye movement data offline.

  • Option #3: Use the EyeLink Host PC to relay TTLs to the BioSemi USB receiver. One can use this solution if there is no parallel port on the Display PC. You send a commend to the EyeLink Host PC to request it to send a TTL to the BioSemi USB receiver; of source, we would also like the EyeLink Host to log the same TTL signal in the eye movement data.


Integration via Experiment Builder

Detailed instructions for Experiment Builder users can be found in the PDF documents which accompany the BioSemi Example Templates provided in Experiment Builder 2.2 and above. The PDF documents are linked below. For Solution #1 and #2, you can use either the BiometricTTL node (recommended) or the setTTL node in Experiment Builder to send TTLs through the parallel port on the Display PC.

.pdf   Biosemi_EyeLink_Simple.pdf (Size: 3.08 MB / Downloads: 65)

.pdf   Biosemi_NonEyeLink_Stroop.pdf (Size: 2.86 MB / Downloads: 25)

Integration via other Stimulus Presentation Software

People using E-Prime should consult PST / the relevant manuals for guidance.

For MATLAB+Psychtoolbox, NBS Presentation, PsychoPy, OpenSesame, and other stimulus presentation software, synchronization can be done via TTL signaling. An introduction to TTL signaling outlines the basics of TTL signaling. 

Users should mark critical trial events by simultaneously sending a TTL to the EEG equipment (typically via the parallel port of the Display PC) and writing a message to the EyeLink data. Alternatively, if you have a Desktop Host PC with a parallel port, a DB25 Splitter cable can be used to send the TTL to both the EEG equipment and the Host PC.

Offline synchronization in EEGLab and Fieldtrip

For offline synchronization in software such as EEG-LAB and Fieldtrip, if Option #2 is being used, it can be useful to ensure that the message sent to the EyeLink ends with the same 0-255 value that was sent as the TTL.