(Note: This experiment was inspired by a Reddit user who recently posted a graph showing their heart rate while watching the movie Interstellar).
Last week I went to see Interstellar (in IMAX, for full sensory effect!) and captured some biometric data to see how I reacted during the course of this nearly 3-hour movie. I wore a Polar H7 heart rate monitor paired with the SweetBeat HRV app on my iPhone, along with my wrist-worn Basis B1. I exported the raw data from SweetBeat using their built-in export tool, and my Basis data using my Basis data export script.
Whereas the original experimenter only tracked heart rate, I wanted to analyze:
- Heart Rate
- Heart Rate Variability (HRV)
- Galvanic Skin Response (GSR)
Interestingly, my heart rate trend (on the left, below) looks very similar to the original Reddit user (on the right)! Both of us are using data from our wrist-worn Basis devices – in my case, the older B1 model, and for the Reddit user the newer Basis Peak. Although the Peak is capable of capturing more samples, the data returned from Basis is always an average value for each minute.
However, SweetBeatLife is recording data at a resolution of 1 sample per second via the Polar H7. The per-second pulse data is a little bit jumpy and hard to follow (in gray), so I’ll also include a 60-second moving average as well (in blue):
It looks very similar to the data recorded by my Basis. Good!
Heart Rate Variability (HRV)
Heart Rate Variability uses a technique in which the spaces between heart beats are measured, and is a good way to measure stress via an individual’s “flight or fight” response (the higher one’s HRV, the better). There are a number of ways HRV can be calculated, and in this case we are using what’s known as rMSSD (root mean square of successive differences). You can check out Wikipedia for a pretty good overview of HRV.
Galvanic Skin Response (GSR)
Galvanic skin response (also known as skin conductance) can be used as an indication of psychological or physiological arousal:
My GSR started out rather elevated, which I guess was due to a combination of anticipation for the movie to begin as well as my eyes getting adjusted to the huge IMAX screen (and my body adjusting to the temperature in the theater). I was clearly into whatever was happening on-screen between 1:50 and 2:20!
Putting It All Together…
Now, if we look at all of the visualizations together, we can easily spot key moments in the movie (no spoiler alerts here, but if you’ve seen the movie you should be able to figure out what was happening in each area!), or when I might be internalizing some deep analysis of gravity and multidimensional spacetime, or simply bored (the movie takes some time to really get going!). We can also see when my stress response kicks in or relaxes (phew!).
Looking back at the data, you’ll see there is often an inverse relationship between heart rate and HRV, which makes sense – if your heart starts beating faster, you are most likely encountering more stress, which increases your sympathetic response and thus lowers HRV. Galvanic skin response typically is reflective of one’s sympathetic autonomic nervous system response (will increase as HRV decreases).
I think a great experiment idea would be for a bunch of self-quantifiers to all go see the same movie so we can all share and compare our data! Shoot me an email if you’d like to get involved.