Thinking Fast and Slow – test for psychological arousal

If you’ve never heard about Daniel Kahneman or his book Thinking Fast and Slow you really ought to check it out. It’s all about how our brains can be fooled essentially because we’re lazy at thinking. But one of the key ideas in the book is that there two modes of thinking – fast and slow. But this idea isn’t just out of thin air because there is a psychological response when your turn your brain on and I wanted to test it.

While I initially suggest taping a bobby pin with a small lens out of a toy laser onto your phone to record with – this is a bit difficult due to the very short focal length. Through trial and error I settled on a fairly simple setup. First I took a pair of Reel 3D glasses from the movie theater and removed the lenses. Next I held the clip on macro lens up to the left hand eyepiece to measure how much material I needed to remove to get the lens to fit into the frame.

The goal is to get the macro lens to pressure fit into the glasses frames. Additionally it’s important to put the lens on the left eye due to how the iPhone camera lens is oriented. This placement allows the body of the phone to be up and above the nose while recording. If placed on the other eye either the subject’s nose gets in the way or the phone has to be far off center leading to balancing and alignment issues.

Anyway, I carefully dremeled out a small amount of the frames at a time to fit in the macro lens. The macro lens was then wedged into the frames facing where the eye will be and the clip for the phone facing out. Also the clip was angled so that when the phone was on the body of the phone and hence the weight was balanced centrally and above the forehead when worn.  Finally additional rubber bands were placed to help keep the lens from pivoting while the phone was clipped in.

Once this is in hand you need to find your victims subjects and set up a good lighting situation. The lighting is very important if you are going to be able to test your subjects response. I found that lighting the eye from beneath with a flashlight worked the best as it lit the whole area of the eye up without the subject accidentally looking into the light and causing their pupil to contract.


Plastic frames (3d glasses with the lenses punched out), a clip on Macro Lens (I used this from Aukey: , some rubber bands, a smartphone with a camera, a flashlight or other bright light source.

Exercise Procedure for each Subject:

  1. Before asking the subject to wear the recording apparatus make sure it’s in good condition and won’t fall apart during recording. Also check that there is sufficient lighting available.
  2. Turn on the camera function of the smartphone.
  3. Next demonstrate how to wear the apparatus, it’s likely your phone up there you don’t want them to drop it.
  4. Next allow them to put it on. You should be able to see if any adjustments need to be made to position the glasses. Everyone’s face is different and to save time I just asked my participants to raise or slide the glasses around a bit to center their pupil.
  5. Double check that the lighting and focus is working.
  6. Press record on the smartphone (I forgot this 2 times on the 5 people I tested).
  7. Next explain that you are taking a baseline and all they need to do is repeat some random sets of single digit numbers back to you.
  8. Give them 3 sets of 3 single digit numbers to repeat back to you (wait for them to reply before starting the next set).. You can write these out ahead of time or make them up on the spot. The former is more controlled but I didn’t bother so whatever fits your needs.
  9. Next ask them to repeat the numbers back the number plus 1. Then give a simple example like: “If I say 2 you say 3. Got it?” This is the plus 1 exercise.
  10. Once they understand give them 3 sets of 3 numbers again this time waiting between each set for them to reply with their answers. Again you can write them down for better control but it isn’t necessary.
  11. Next ask them to do the same thing as they just did but this time adding 3 to each number. Then give an example like: “If I say 5 you say 8.” This is the plus 3 exercise.
  12. It is a good time to check that your focus and recording is still working before proceeding.
  13. Now give them 3 sets of 3 numbers again, while waiting for their responses between each set. Again you may want to write sets down for consistency.
  14. Once complete thank the participant and tell them they can take off the recording apparatus. Once they give it back you can stop the recording on the smartphone.


Tips for getting good results:

  • First off don’t worry if your participant doesn’t get the right answers, this isn’t a test of skill. Just note it in case you want to give an additional set  of numbers.
  • Likewise don’t ask too many sets of questions, while you may want more data the participant might get fatigued and their emotions will interfere with the results. I found three runs allowed for at least one solid trial with each person without taking too long.
  • Try to have fairly bright ambient light, but not too bright. If the ambient light is very dim the amount of dilation available is smaller so the effect is diminished. Likewise if the lighting is too bright the effect might be hidden because the pupil is responding to the light more than the thinking.
  • If you are having trouble seeing a dilation response on a particular subject try sneaking a large-ish number into one of the sets. For instance, if you give the subject a 7, 8 or 9 during the plus 3 exercise they are forced to think of a second digit. I found that there was always a marked response when I did this.
  • Deliver the numbers at a constant speed. As you saw in my video, since I was making the numbers up on the spot, I spaced out the numbers to a point when the subject didn’t have to hold all the digits in their head. On the other hand it might be interesting to vary this spacing and see what the response is.


Data Preparation:
Depending on your environment and the quality of video you may be able to review your results directly on the phone. However, in my case I had some lighting issues as well as wanting to show the footage of each individuals face. So I began by importing the footage into the computer and then I did some very basic color correction (brightness and contrast) to each of the pupil videos to enhance contrast between the iris and the pupil. Next I timed these by the audio on the video with the footage if he subject straight on. Finally I scaled down the pupil footage to somewhere in the frame so that I could see both the person and the dilation. In hind sight maybe I should have flipped the pupil footage to be the big background one and the subject to be the small one in the corner but oh well.


If you want to watch the full length tests of everyone (Plus myself):

Analysis and Results:
Only after I got the footage timed and arranged did I really examine each moment to try and spot the dilation. It was definitely easier to see at some times than others and the amount of dilation varied a lot.  I mostly used the baseline of them repeating the numbers back to me to identify if they were nervous or if the lighting would invalidate the results. However, while some trials were darker than I would have liked the lighting didn’t cause too much of a problem and typically repeating the numbers would help relax the participant.

Next while examining the plus one set, I only got a few reactions. This wa expected from what was outlined in the book. The exercise to add 1 to a set of 3 numbers was stated as not always engaging system 2, or slow engaged thinking.

As I mentioned in the video I did see a result after the plus three tests at least once for each participant. One person made mistakes and the accompanying emotional response when realizing what they had done invalidated those sets but the third version had a clear response. Likewise, I had one run when the dilation only happened at the beginning and the participant stayed engaged there after. However, this seemed to happen in the dimmer situations situations, suggesting that I probably just missed some of the more subtle movement in cases where the pupil was already wide open.

More on the book can be found here:,_Fast_and_Slow  

But really just read the thing – I could put an amazon link but it’s an old enough book you can probably find it cheaper somewhere else or just get it from your local library.


Featuring (Test Subjects):

Nick Lucid –

Sally Le Page –   

Peter Musser –

Jonathan Pfahl –

Emily Lucid

Stuart Stent

Special Thanks to Thinkercon for putting an event together that spurred me to get this project together.


More info on System one and two thinking:


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