Nearly every EEG research lab needs to send triggers from the experimental setup to the EEG system. Of course, the solution should be precise, reliable and easy to use. By using the USB port and the Brain Products TriggerBox, one can send triggers to the EEG amplifier with a precision of less than 1 ms. If you are using E-Prime® 3.0 or Presentation® 20.0 and have a USB port available, you have a plug & play solution for triggers.
The parallel port was used for sending triggers to EEG recordings. However, it becomes increasingly problematic to find a computer with such a port. Luckily, we have a product that is able to address this problem: the TriggerBox. By emulating your old parallel port by means of a virtual serial port, the TriggerBox allows you to send accurate triggers via a USB port. In this article, we show you how to use the TriggerBox to send triggers via USB with E-Prime 3.0 (Psychological Software Tools, Inc.) and Presentation 20.0 (Neurobehavioral Systems, Inc.). We provide source code examples for each software package so that you can follow our step by step instructions yourself.
In most EEG experiments we would like to co-register events with our EEG data. For example, we might need markers that indicate the timing of stimuli and responses. The standard approach to send markers to the EEG recording is via TTL pulses. Until recently, the only reliable way to send TTL triggers to the EEG amplifier was using the parallel port or an I/O card. However, in most modern computers, specifically laptops, a parallel port is not available, and using extension cards bears the risk of chipset, BIOS, or operating system incompatibilities. Also, recent operating systems and programming environments do not support parallel port communication. Therefore, we have developed the USB based TriggerBox that emulates the parallel port by means of a virtual serial port. By emulating your old parallel port, it permits the USB port of your computer to be used as an 8-bit trigger source.
Including the TriggerBox in your setup is very easy and intuitive
Performing these steps will allow you to check whether the setup is functioning correctly before trying to implement your own experiments. If you do not see any markers after following the previous steps, please contact the Brain Products Technical Support team .
Figure 1: Standard setup to record EEG and USB generated markers. TriggerBox links the USB output of your PC with the trigger input of your amplifier.
The TriggerBox is a versatile product, able to receive triggers from different sources, combine them, and then forward them to an EEG amplifier. For those interested in further details, you can find them in this newsletter article.
We have described what the TriggerBox can do and also walked you through the setup and testing procedure. Now let us guide you through some practical examples using E-Prime 3.0 and Presentation 20.0. In just three basic steps you will have your system ready to send triggers using the USB port. Below you will find detailed instructions for these three steps.