Wireless Trigger – a fully mobile solution for recording event markers in EEG data

by Dr. Davide Riccobon
Usability Manager (Brain Products
)

Let me take you on a short tour around our newest product, the Wireless Trigger, in combination with our well-established wireless amplifier, the LiveAmp. I will show you the possibilities the new technology offers and share some tips and tricks for working with the Wireless Trigger.

In 2015, Brain Products released a new amplifier to the market: the LiveAmp. It stood out through its small size and versatility. Since then this tiny amplifier has been used for a great number of experimental setups.

LiveAmp can be used like any other wired amplifier for stationary lab purposes, for example in ERP studies. In this case, triggers are supplied to the amplifier in a very accurate way by means of a trigger cable and the Sensor and Trigger Extension Box.

Wireless Trigger Set: Receiver (left) and Transmitter (right)

Wireless Trigger Set: Receiver (left) and Transmitter (right)

Beyond stationary applications, the LiveAmp is your perfect companion for all studies where EEG participants cannot be bound to a laboratory. The possibility to record data directly to a memory card without any connection to a recording computer, allows participants to move freely. But what about experiments where both moving freely and having accurate triggers are required?

Now, we have the solution: We are proud to present the Wireless Trigger. It consists of a Transmitter and a Receiver device. The Transmitter is plugged into a trigger source such as a parallel port. In the case that a parallel port is not available, you can also use our TriggerBox instead. The Receiver is connected to the trigger in port of the Sensor and Trigger Extension box (see images below).

Picture 2 (left): Connecting the Wireless Trigger Transmitter to the TriggerBox; Picture 3 (right): Connecting the Wireless Trigger Receiver to the Sensor and Trigger Extension

Left: Connecting the Wireless Trigger Transmitter to the TriggerBox. Right: Connecting the Wireless Trigger Receiver to the Sensor and Trigger Extension

This is all you need to do: just replace a trigger cable with the Wireless Trigger.

Actually, you could already start with your experiment, but if you wish to gain some more insights… then keep reading: it’s time to explore the details of your wireless system! To begin, set up your complete system, including the stimulation device (PC, Laptop, signal generator …); and don’t forget a moving participant: now, we are completely wireless!

I suppose you have already connected BrainVision Recorder to the LiveAmp and you have started the Recorder monitoring mode as well as your stimulus presentation software. You may start your favorite experimental paradigm that generates triggers, but a repetitive pattern of triggers (e.g. with a frequency around 5 Hz) may be easier to observe visually. If you have our TriggerBox ready at hand, you may also use the TriggerBox Test IO app for the generation of triggers. As soon as you start the generation of triggers you should see them showing up in Recorder.

As you can see, the Wireless Trigger is as easy to use as a normal trigger cable. It is important to know, however, that a wireless connection behaves differently than a wired one. The transmission range of the Wireless Trigger is limited to 10 m and triggers can be lost when there is interfering RF activity in the environment. Therefore, you should always test the RF environment before you start with the real experiment. We recommend testing the transmission of triggers before recording in an unknown environment. Please also look for interfering Bluetooth and WiFi devices (e.g., using a WiFi-sniffer) and switch them off, if possible, to minimize the RF noise.

By the way, you can use an LPT-to-LPT trigger cable (supplied with the TriggerBox) to connect the TriggerBox with the Transmitter (in this case you will also need an external power source like a power-bank; please refer to the Operating Instructions for more information). This way you can choose a better, more central place for the Transmitter, maybe even on the ceiling.

Now, we have learned the most important things about the use of the Wireless Trigger. There is only one important question left: Can we process the recorded EEG data the usual way? Yes, but you need to know one thing: data transmission from the Transmitter to the Receiver requires 3 ms ± 1 sample. This means that between EEG and Trigger there is a constant delay of 3 ms, and a jitter of 1 sample. If you want to compare data recorded with the Wireless Trigger to data recorded using a trigger cable, you need to correct the additional 3 ms in the Wireless Trigger data. You can do this very easily in BrainVision Analyzer 2 using the “Edit Marker”-Transformation as shown in the screenshot below.

Picture 4: Edit Marker Transformation in BrainVision Analyzer 2

“Edit Marker” Transformation in BrainVision Analyzer 2

To minimize jitter, select the highest sampling rate available for your given channel configuration (e.g., 1 kHz for 32 channels). 

That’s all from my side. Now, it is your turn.  Do you already have a LiveAmp system and you are just waiting for the Wireless Trigger? Are you new to this field but interested in the new possibilities given by our wireless system? Don’t hesitate to contact sales@brainproducts.com or your local distributor. We will be happy to give you more information.

©Brain Products GmbH 2018