Galvanic Skin Response Computer Mouse


Introduction: Galvanic Skin Response Computer Mouse

A current trend in human computer Interaction research is to use physiological measurements to gather data while users are engaged in the software or website which is being tested.

A big problem, however, is that the users do not tend to feel at ease when they are connected to these complex hardware systems. This may hamper the elicitation of natural behaviour. Therefore non obtrusive measuring tools need to be created.

This instructable is a first attempt in that direction. A Standard old Dell computer mouse was outfitted with GRS electrodes. This way physiological data can be gathered withour hampering the user.

Step 1: Preparation

What you need:

- A computer mouse
- a drill
- 2 AA batteries
- tape
- Thin electric wire
- Connectors

Step 2: Preparing the Mouse - 1

This step basically shows you how to dismantle the mouse. We need to remove the buttons to fit the electrodes.

Mouse types may varty, but the two I worked on were rather similar.

Step 3: Preparing the Mouse - 2

The pictures will show you where the holes need to be drilled.

the middle of each button should be the place to drill to add the electrodes.
Basically choose the place which seems natural to you. the electrodes should connect to the tops of the fingers (where ones finger prints are).

Another 2 holes need to be drilled in the mouse structure itself in order to pass the wires

Step 4: Placing the Electrodes

I used the + pole of a standard AA type battery as this is the ideal shape and size for the job.
Do not use Duracell batteries as they weld the poles to the core.

Carefully remove the casing of the battery without harming the core.

Remove the positive and negative poles of the battery. these are usually glued to the chemical core, you shouldn't harm the chemical centre of the battery during this step.

The following steps are clearer by following the pictures. the show how to attach the wires and fix the electrodes in the right place.

Step 5: Finishing and Testing

Reassemble you mouse.

Attach it to you bio measuring device and test it.

To give the mouse a finished look you could use electric tape to tape the wires together.

don't be afraid that users might lift their fingers off the electrodes. A disconnection gives a very clear signal which can be easily filtered out.

The device you use to acquire the data may differ off course. Our lab uses the MP100 system by Biopac. Its an extensible lab giving you the options to add multiple measuring devices. To date we only have the GSR unit and a ECG unit. The advantage with this unit is that is has the ability to synchronise with the Noldus Observer software. This package is used by many usability and behavioural labs to gather observational data.



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    cool! You might try gripper snaps (available at craft & sewing stores) for the electrodes to avoid dismantling batteries. what hardware & software are you using to collect & look at the data?

    Why not move the sensors off the buttons, which move and have to allow for both movement and increase/decreases in pressure when clicking? Why not move them to the body of the mouse? Where the palm sits might actually give you better data, since the palm is less likely to expand or contract, thus altering the signal in that way and the pressure likely stays fairly constant. An even better control on the surface might be a trackball, like the ones logitech has. It would mean less movement in general, since the mouse stays put, and it has a nice place for the palm to rest. I'm not a GSR expert or anything, just my two cents.

    3 replies

    Using the palm sounds like a better idea because the pressure put on the pads when the user clicks the mouse will give a faulty reading. The pressure on the palm would probably be much more uniform.

    My palm doesn't really rest on my mouse. The ball of my hand rests on the mat and my palm and fingers move the mouse.

    The palm would be worth considering. I will look into that option. A trackball I would rather not use, as this again is an odd device for many users, and we want them to interact with the software or product being tested in the most natural way as possible.

    Nice idea. You will have do quite bit of work if you wan't valid results with this setup for two reasons: - You need a fixed distance of skin between the electrodes if you want to compare the individual measurements. Movement will change the resistance. - Your electrodes may be subject to polarization rendering the measurements worthless. You want to look for Ag/AgCl electrodes.

    1 reply

    What exactly would be the advantage of the Ag/AgCl electrodes? Im a psychologist just getting into the world of DIY so I do miss some knowledge on material choice, and more. So if you could give me some info on those electrodes it would be great.

    Hmm, GSR is just measuring conductance or capacitance of human skin I think, depending on if it's active or passive. I'm not sure what exactly a bio-meter does but you can perform and log those measurements without anything fancy... An arduino should be able to I'd think. I' may just have to try making a GSR device with an arduino :-)

    1 reply

    Keep me posted on your work with the arduino, that would make it a really cheap solution, in stead of the commercially available, and expensive Biopac unit we use.

    Years ago Wendy Ark at IBM built an "emotion mouse" that also measured electrodermal activity (EDA). (GSR is a dated term for this phenomenon.) Prior to that we had started to put EDA sensors into a steering wheel, only to realize that there were a lot of pressure and motion artifacts with EDA on active fingers. One concern with the accuracy of putting EDA in the mouse is that increasing the skin pressure against the electrodes increases the skin conductance signal. Carson Reynolds and I showed in studies at MIT that people tended to apply more pressure to the mouse when stressed. While the error is in the right direction (skin conductance usually goes up with stress) it is the case that the mouse-captured signal won't match the std EDA signal generated with constant pressure. Also, left-right comparisons won't be identical due to the fact that the signals on both sides of the body are controlled separately by the two sides of the brain, making it hard to test how good the new sensor is compared to a commercial one. All of this aside, a sensor that measures increasing pressure and skin conductance on the mouse could be a very helpful tool for reflecting on one's internal state, and on how this is interacting with the task on the computer. This mouse looks like a great tool for exploring these interactions, even if it is not identical to the standard physiological measures for EDA.

    1 reply

    Hi thanks for this comment, i hadn't heard about the research you mentioned before. The Game Experience Lab at the Technical University of Eindhoven is actually experimenting with a computer mouse with integrated pressure sensors. If you feel that the combination of pressure and GSR would prove useful I should contact them and see if we can work together. Great to learn from other people this way

    How about instead of using the tip of a battery (which is rather big), drill several small holes that leads to a thin iron rod, like, a paperclip, which will have lesser surface area, and less of the 'aware'-able temperature difference between the metal and the plastic. I'm not so knowledgeable about this, so if I happen to understand or interpret something wrongly, my apologies.

    what would be even better would be a conductive surface covering the mouse buttons for extra comfort so the user could forget that its a modified mouse :) and add to relaxation.

    3 replies

    It wouldn't: Since you want to measure conductance as accurately as possible you don't want to add contact surface as a variable in you measurement. Nice idea though!

    Hi Bongmaster, The posted mouse is actually my fourth prototype. The versions before included really basic things like gluing a paper clip onto the buttons, and as you are suggesting mouse buttons completely covered in a conductive surface. This version,however, did not pass our tests as even the slightest movement caused a different part of the finger to pass the signal which kept skewing our results. Our conclusion was that the conductive surface has to be as small as possible, and keep the fingers from too much movement. But thanks for your comment, I hope improved ideas will emerge.

    kool :) hope u get the results u need :)

    Hi, thanks for your comment. When it comes to data, all we have been doing is small tests in our lab and checking variables as movement, finger release, and performance over a longer period to compare it to our data from the standard GSR. What I would like to do is hook a person up to a standard GSR on one hand and the GSR mouse on the other, but as we only own one Bio Unit I cannot do this yet.