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.

Everything ends up in one record on the BioLab PC. The physiology gets there over wifi. The two streams that have to be timed against it get there on a wire.

How the physiology reaches the PC

The MindWare Mobile sits on the participant and sends its data over wifi. That wifi comes from a dedicated router supplied with the Mobile, and the router is connected to the BioLab PC by a LAN cable into the PC Ethernet port.

So the participant can walk. The BioLab PC sits at the far end of an Ethernet cable and never joins the wireless network itself.

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 MindWare TTL cable has an LPT termination on both ends. On the stimulus PC side it plugs into a USB to LPT converter supplied by MindWare, and the other end of the cable runs to the BioLab PC.

Most PCs no longer have an LPT port, which is usually the case on the BioLab machine too, so in practice a second converter goes on that end as well. Count the ports before you order.

E-Prime or Python sends the code, and the TTL events are registered in millisecond accuracy, side by side with the ECG and the skin conductance in the same record.

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 running a Chronos for responses, add the MindWare adaptor for it. The regular MindWare TTL cable then fits the Chronos, and the other end goes to the BioLab PC exactly as above, through a converter if there is no LPT port. Response marks and stimulus onsets end up on the same path.

The glasses come in as a fifth channel

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

The Tobii recording unit outputs its signal on an AUX cable. The far end of that cable has a special termination that fits the 5th channel on the MindWare Mobile, so the glasses record straight into the physiology file alongside the ECG and the skin conductance.

What that channel carries is the Tobii Glasses 3 clock. A rectangular signal every 10 seconds, which shows up in the physiology file as a clean pulse train.

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 cable 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.

More than one participant in the room

Worth knowing before you design the protocol. The physiology system acquires from up to 8 participants at once, all recorded to the same BioLab PC. A dyad or a small group task sits in one record.

Running several Tobii Glasses 3 at the same time is a separate question and the answer depends on how you want to acquire them. Talk to us and we will go through the options.

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. The wifi link is there to carry the physiology stream. The marks you intend to analyse come in on a cable.

Observer XT sits outside the acquisition 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. Observer XT accepts external data from BioLab, from E-Prime and from the glasses, so video, physiology, stimulus events and gaze all sit in one project on one timeline, and you add behavioural codes on top of them.

The alignment itself 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

• Confirm the Mobile connects to its router and BioLab finds it, before anyone is wired up
• Check both ends of the TTL run for an LPT port, and order a converter for whichever end does not have one
• 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?