Physiology, video and gaze in one observation lab

This lab has more moving parts than most. Physiology on a MindWare Mobile, cameras and microphones on MediaRecorder, a stimulus PC running E-Prime or Python, mobile eye tracking on Tobii Glasses, and The Observer XT for the coding.

Five systems, and people assume five clocks. In this configuration there are not.

Nearly everything arrives at the MindWare Mobile on a wire, and the wire is the reason it works.

Video and physiology

BioLab starts MediaRecorder. The physiology record and the video share a start point, and you do not set that up again for each session.

That is the spine of the room and it is already solved. What follows is the two streams that have to be tied to it.

Stimulus onsets

The stimulus PC marks the physiology through a USB to serial converter from MindWare. E-Prime or Python sends the TTL, the converter passes it to the MindWare Mobile, and the onset is written into the same record as the ECG and the skin conductance.

That is what puts stimulus and physiology on one timeline. Not a post hoc alignment, not a best guess from a log file.

If you are already running a Chronos for responses, it can send triggers to MindWare hardware from E-Prime 3.0, which keeps the response marks on the same path as the onsets.

The glasses come in as a fifth channel

This is the part people expect to be hard, and it is not.

A cable runs from the Tobii Glasses recording unit into the MindWare Mobile, and the glasses arrive as a fifth channel. They send a rectangular signal every 10 seconds, so what you get in the physiology file is a clean pulse train from the eye tracker.

You align the gaze data on that pulse train. A mobile eye tracker with its own clock, on a participant who is walking around, tied to the physiology by a wire and a repeating square wave.

Check the pulse train is present and regular in the physiology record before the participant leaves. If the cable was not seated, that is the moment to find out.

The one shortcut we would not take

BioLab accepts UDP commands to start acquisition, stop it and log events over the network. It is easy and it needs no hardware.

MindWare say, in their own documentation, that UDP is subject to network and processing delays and is not a substitute for external trigger and event lines when precise timing is required.

Take them at their word. Network for control, wire for the marks you intend to analyse.

Observer XT sits outside the sync

This surprises people, so it is worth saying plainly. The Observer XT is not part of the acquisition synchronisation, and it does not need to be.

It is where the coding and the analysis happen, after the session. Video, physiology and gaze all arrive there already carrying one timeline, because the alignment was done in hardware while the data was being recorded.

Which puts the weight on the cabling. Get the wires right and Observer XT has an easy job. Get them wrong and no amount of work in Observer XT recovers the timing.

What is tied to what

Where we would not spend the money

If the protocol is a seated screen task and the participant never leaves the chair, the glasses are the wrong instrument. A screen-based tracker gives you higher sampling rates and a simpler cable run for less money. Buy glasses when the participant has to move, and not before.

The same applies to camera count. MediaRecorder scales to eight, and eight angles of a room where nothing happens in six of them is eight streams to store and review. Specify the angles you will code.

Before the first participant

• Send a known sequence of event codes and confirm every one appears in the BioLab record
• Confirm the glasses pulse train is present in the physiology file and arriving on schedule
• Run a full-length dummy session, then compare the first minute against the last
• Import one complete dummy session into Observer XT before you run a real one
• Label the cables. In a room this dense, a swapped cable costs a whole session

The parts

NBT supplies MindWare, Noldus, Tobii and Psychology Software Tools in Israel, and installs them.

Send us the protocol and the room, and we will tell you what has to be wired and what does not. Is the participant staying in the chair, or moving?