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Browse the departmentA Cedrus device for synchronizing stimuli with the Tobii Pro Spectrum eye tracker and an EEG or physiology recorder. A light sensor on the screen detects when the image actually appears — regardless of system and graphics card delays — and StimTracker sends the same marker to all recordings at once.
In a study with an eye tracker or EEG, every stimulus gets a timestamp — an entry saying “the picture appeared at this moment”. It is usually sent by the stimulus presentation software when it issues the “show” command. But between the command and the image on the screen there is still the operating system, the graphics card and the monitor itself. The image appears later, and how much later changes from trial to trial. See consecutive trials at a station with Tobii Pro Spectrum and EEG.
Illustrative graphic in slow motion — the gaps are randomized by the browser and are not measurements. Photo: Tobii (Tobii Pro Spectrum with a Brain Products EEG system).
StimTracker does not ask the computer when it showed the stimulus — it looks at the screen. A small light sensor attached to the monitor notices the change in pixel brightness, and the device turns it into an event marker and sends it simultaneously to the eye tracker and to other recorders.
EyeTracker TTL in event.
Duo: up to 2 light sensors, audio, response pad and USB codes; 2 m-pod outputs — e.g. Tobii Pro Spectrum and EEG.
Quad: up to 4 light sensors, microphone (voice key), 3 TTL inputs; 3 m-pod outputs and a direct TTL output — up to 4 recorders at once.
Light sensor — 8 × 20 mm, 2 m cable with a 2.5 mm jack plug (can be extended). A white and a black one are included, with notches that make positioning on the screen easier.
StimTracker works with Tobii Pro Spectrum — an eye tracker with a TTL input for hardware synchronization. The connection is a ready-made m-pod for the eye tracker’s TTL input — Cedrus describes it as a “plug and play” integration, with 8 bits of data per event.
Eye tracker
AnalysisStimulus changes detected by StimTracker are visible directly in the eye tracking data in Pro Lab — or you export them to other analysis software.
Yellow marker drawn for illustration on a Pro Lab screenshot.
StimTracker also accepts event codes via USB. The latency depends on the driver the software uses:
Any software that controls the eye tracker through the Tobii Pro SDK also works. The light sensor does not depend on the software — it always marks the image on the screen the same way.
Every device in the lab records data according to its own clock. To relate where the participant was looking to what was happening in the brain or the body, all recordings need a common reference point. StimTracker sends the same marker to all of them at once — according to Tobii, synchronization with EEG is accurate to about one sample (1 ms at 1 kHz sampling).
An m-pod comes configured for a specific recorder model. The manufacturer lists, among others:
The signal traces on the photo are illustrative, not a recording from the device. Photo: Tobii.
A marker from the software is the simplest route and is often enough. When milliseconds matter or several devices need a common timeline, hardware synchronization stops being an add-on. This is how the two routes compare according to the manufacturers:
| Feature | Marker from software | StimTracker with light sensor |
|---|---|---|
| What it marks | the moment the “show” command is issued | the moment the pixels on the screen actually changed brightness |
| System, graphics card and monitor delays | go into the result | have no effect — the sensor looks at the screen |
| Accuracy with Tobii Pro Spectrum | depends on the software and computer | below 1 ms for visual stimuli |
| Several recorders | the marker has to be sent to each device separately | the same marker to 2 (Duo) or 4 (Quad) devices, 0 ms difference between m-pods |
| Sound and voice | the moment of the play command | onset of sound and verbal response (Quad) — after the threshold is crossed |
Sources: tobii.com (StimTracker, Tobii Pro Spectrum), cedrus.com (StimTracker — specifications). As of 2026-10.
We select the model and m-pods for your devices, combine the eye tracker, EEG or BIOPAC and the stimuli into one station and train your team.
Both models send markers simultaneously to Tobii Pro Spectrum and to a second device — EEG or a physiology system. Quad adds a voice key, more light sensors, TTL inputs and more outputs.
| Feature | Duo | Quad |
|---|---|---|
| Light sensors | 2 | 4 the 4th sensor shares a connector with the microphone |
| Voice key (microphone) | — | yes |
| TTL inputs for external events | — | 3 |
| m-pod outputs at once | 2 | 3 |
| Direct TTL output | — | 1 |
| Audio, RB-x40 pad, USB codes | yes | yes |
| Raspberry Pi board (option) | — | yes |
Additional m-pod for EEG or BIOPAC — optional.
According to Cedrus specifications (StimTracker Duo and Quad) and Tobii (integration with Tobii Pro Spectrum).
| Parameter | Value |
|---|---|
| Light sensor | |
| Response time (dark → light) | 0.05 msresponse and recovery times depend on the amount of light |
| Recovery time (light → dark) | 4 ms |
| Spectral sensitivity | 360–970 nm |
| Dimensions and cable | 8 × 20 mm; 2 m cable, 2.5 mm mono jack (extendable) |
| Latencies | |
| Event registration | < 5 µs from event to registration and timestamp |
| Input → output | light sensors < 0.01 ms (excluding sensor response time); audio and voice key < 0.05 ms after the threshold is crossed; responses < 0.01 ms |
| Output to m-pod / USB | < 200 µs on the m-pod pin; < 100 µs to the USB port |
| Difference between outputs | 0 ms between m-pods; 0 ms between m-pods and the TTL output (Quad) |
| Event codes via USB | 2 ms constant, no jitter — Cedrus C++ and Python (pyxid2) libraries, SuperLab, PsychoPy±5–6 ms via serial port emulation, e.g. E-Prime |
| With Tobii Pro Spectrum | |
| Visual stimulus marker accuracy | below 1 ms |
| Timestamp in the eye tracker | 50 µs, regardless of the sampling rateSpectrum TTL input: 8-bit, DB-9 connector |
| Synchronization with EEG | approx. 1 recorder sample (1 ms at 1 kHz) |
| Event in Tobii Pro Lab | EyeTracker TTL in in the recording; export to other software |
| Device | |
| Inputs | Duo: 2 light sensors, audio, RB-x40 pad, USB · Quad: 4 light sensors, audio, microphone, RB-x40 pad, 3 TTL inputs, USB |
| Outputs | Duo: 2 m-pods · Quad: 3 m-pods + 1 direct TTL; both: USB output with timestamp |
| Functions | asynchronous output, signal filtering, pulse generator, scheduler, pulse offset between devices |
| Power | 9 V, 5.5/2.1 mm plug (center positive); 250 mA + 50 mA per m-pod |
| Weight with packaging | Duo 1.09 kg · Quad 1.18 kg · m-pod 0.36 kgpackaging 26.9 × 21.1 × 7 cm (with m-pod 11.5 cm) |
| Software | Tobii Pro Lab, Tobii Pro SDK; SuperLab, PsychoPy, E-Prime, Presentation, Inquisit, Experiment Builder, MATLAB, Python, C++; m-pod configuration: Xidon 2 |
| Manufacturer | Cedrus Corporation (USA) |
Sources: cedrus.com/stimtracker (specifications, FAQ, Tobii and BIOPAC integrations), tobii.com/products/accessories/stimtracker. As of 2026-10.
For many studies — e.g. fixation analysis on images or web pages — synchronization in Pro Lab is enough. StimTracker is useful when individual milliseconds matter (reaction time, single-frame stimuli) or when the same marker also has to reach an EEG or physiology system. Describe your study to us — we will advise whether you need it.
With Tobii Pro Spectrum — an eye tracker with a TTL input (8-bit, DB-9 connector). Markers go into the Tobii Pro Lab recording as EyeTracker TTL in events.
On the area of the screen whose brightness changes together with the stimulus — so that it does not cover the stimulus itself for the participant. The sensor measures 8 × 20 mm and has notches on three sides that make positioning easier; a white and a black one are included. We help choose the placement during installation.
Yes. Both models mark the onset of sound played through StimTracker and key presses on the Cedrus RB-x40 response pad. The Quad model additionally detects the onset of a verbal response (voice key with a microphone) and accepts TTL signals from other devices.
Yes — through an m-pod matched to the recorder. The manufacturer lists, among others, BIOPAC (markers in AcqKnowledge), Brain Products, ANT Neuro, BioSemi, EGI, Neuroscan and NIRx. Duo supports 2 devices at once, Quad up to 4.
The light sensor works independently of the software. If you also send event codes via USB, SuperLab, PsychoPy and the Cedrus libraries for Python and C++ are the most accurate — 2 ms constant latency with no jitter. E-Prime, Presentation and MATLAB use serial port emulation (approx. ±5 ms).
Yes — book a demo of a station with Tobii Pro Spectrum. Write to us.
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