Triggers and event markers

Precise timing information is essential in EEG and other ExG experiments. The Explore amplifier supports both event markers (software-based) and hardware triggers to synchronize recorded biosignals with external stimuli or events.

Types of Triggers

Button Press (On-Device Marker)

How it works: A short button press during recording inserts an event marker.
LED feedback: Light pink flash confirms the marker.
Storage: Saved in offline recordings and transmitted in online streams.
Use case: Manual annotation of events (e.g., trial start/end).

Software Triggers

Can be sent from:

  • Explore Desktop (manual event marker via GUI).

  • Explore Mobile App (manual event marking via GUI).

  • explorepy (Python) via command line or script.

Format: Logged in data files with prefix sw_.
Use case: Synchronizing with experiment control software such as PsychoPy or Presentation. For highest temporal precision, use Mentalab Hypersync for wireless event marking.

Digital Triggers (8-bit)

The Explore Pro supports low-latency 8-bit digital triggers which are transmitted via USB using explorepy. Each trigger is encoded in the range 0–255 and inserted directly into the data stream. This enables high-precision stimulus synchronization in code based experiment, e.g., using PsychoPy. The trigger information is readily available in recordings in CSV, BDF and XDF format.

When connecting external hardware, proper electrical isolation is required. The usage of the USB isolator (UI) is mandatory when sending 8-bit triggers to the Explore Pro.

How To

To connect, follow the steps below:

  1. Turn on your amplifier

  2. Connect via Bluetooth to the recording computer

  3. Connect the USB isolator (labeled UI) to the amplifier

  4. Connect a USB cable to the presentation PC and the USB isolator

  5. Send trigger information on demand

This trigger can be used in both Bluetooth streaming and offline recording mode. We are providing a simple Python script that demonstrates the usage.

import explorepy
import time

# for independent markers stored only in binary file, we only need to instatiate Explore class
exp_device = explorepy.Explore()

n_markers = 20
interval = 2
for i in range(n_markers):
    exp_device.send_8_bit_trigger(i)
    time.sleep(2)

Recommendations:

  • We recommend not using 8-bit triggers in USB streaming mode as it not not always possible to guarantee low latency in such a scenario.

  • We recommend keeping a low load on the presentation PC to ensure low USB latency.

For any questions please contact us at: support@mentalab.com

It is also possible to send USB triggers to the serial port, e.g. using PsychoPy. If you need help setting this up, contact us at: contact@mentalab.com

TTL Pulse (1-bit)

The Explore Pro can receive transistor-transistor-logic (TTL) triggers for binary event logging. This is useful when interfacing with devices that provide only a single output pulse. For details and the required accessories, please contact Mentalab support (support@mentalab.com).

The usage of the Trigger Isolator (TI) is mandatory when sending 1-bit triggers to the Explore Pro (not included in the Explore Pro default bundle).

Hypersync: Wireless Event Marking

For high-precision wireless event synchronization, Mentalab recommends using Mentalab Hypersync in combination with LSL-compatible stimulation software. This is the preferred method for wireless and highly accurate event marking (<1 ms timing accuracy). Combined with Lab Streaming Layer (LSL), this allowes multiple devices (stimulus presentation computers, and other physiological or behavioural recording hardware) to share a common clock.

If you are interested in this solution for the Explore Pro, contact us for a quote at: contact@mentalab.com

Note that wireless LSL markers can be used with Mentalab Explore without Mentalab Hypersync, but this should not be used for use cases requiring high temporal accuracy, such as ERP studies.

Trigger Handling in Recordings

  • Offline mode: Wired triggers are stored alongside biosignal data in the internal memory and exported together.

  • Online mode: Wired triggers are transmitted in real-time to the host via Bluetooth or USB and saved in recording files.

  • File formats: Supported export formats (.CSV, .BDF+) preserve triggers for later analysis.

Best Practices

  • Verify trigger reception before each experiment (test pulse or software event).

  • For high-precision applications, use digital triggers or Hypersync in combination with LSL synchronization.

  • Document trigger codes (e.g., 1 = visual stimulus, 2 = auditory stimulus) in your experiment protocol to avoid confusion during analysis.