Measuring cognitive load with a tapping test

The software engineering team lead was excited. “We think we have developed a product that is extremely effortless to use compared to our company’s biggest and most successful product.” I didn’t understand. “What do you mean by effortless?” He thought for a few seconds, then asked, “Can you help us prove that using our product reduces the cognitive load on users’ minds compared to using our biggest product to complete the same task?”

As he was saying the words cognitive load, I thought about Dr. Uri Hasson, a Princeton University researcher I knew who puts people through fMRI machines while they use different consumer devices to learn about which areas in the brain light up during usage.

A few days later, we met Dr. Hasson, showed him the new product, and asked if he can help us measure cognitive load. He smiled and said he could but he thinks it is an overkill. “There are much simpler ways,” he turned to me. “Look them up.”

Long story short, he was right. I found two much simpler ways to measure cognitive load; one is called NASA TLX (stands for Task Load Test that was developed at NASA), which is a subjective assessment tool that asks users to rate their perception about workload during task performance. The second technique is a tapping test in which you ask participants to tap their foot once per second while they complete a task. The idea is that if the task or certain parts of it is loading their mind, they will lose track of their other assignment (tapping every second) and by counting those taps, you can easily quantify cognitive load. So that’s what I did.

Using tapping is a simple way of imposing a secondary load on the user. If the study participant’s concentration is focused at processing information other than tapping, it is hard for participants to apply the concentration needed to execute the tapping task. — Miyake (2004)

My awesome engineering team happened to have an accelerometer and they decided to measure taps (pace and G-force) by attaching it to our study participants’ shoes using a simple band. The accelerometer was hooked to my laptop which made it possible to generate amazing visualizations of the frequency of taps.

The participant is using a tablet app, our accelerometer is hooked to my laptop and attached to his left shoe.
Notice how taps are regular (one per second between 543 and 560) and how they become irregular after the 560 mark. That’s when this participant’s mind is loaded.
Examine the areas of the evaluated product where tapping slowed down or stopped. Slow or unrhythmical tapping means the participant was experiencing extra load. Areas where tapping stopped have pushed the participant into cognitive overload. — Tracy & Albers (2006)

If you don’t have access to an accelerometer, you can easily measure taps by placing a video camera on the floor so you can later count taps by watching the video. That worked really nicely for me at a later study when the accelerometer decided not to work.

To wrap up my story, the results of the study proved that the new product indeed significantly reduced users’ cognitive load and it is now available and widely used by millions and millions of free-minded people.

Read more about tapping tests

Tracy, J.P. & Albers, M.J. (2006). Measuring cognitive load to test the usability of web sites. Usability and Information Design, pp. 256–260.

Miyake, Y., Onishi, Y. & Poppel, E. (2004). Two types of anticipation in synchronization tapping. Acta Neurobiol Exp, 64, pp. 415–426.

I’d like to thank Will Howe who served as a pilot participant in my first tapping test study, agreed to all this craziness, and allowed me to share the above photos. I’m pretty sure that this experience made him confident enough to start a full blown modeling career and his own awesome tailor shop, Articles of Style. Way to go, Will.

Tomer Sharon is the author of Validating Product Ideas Through Lean User Research. Get a 20% discount when you purchase the book directly at Rosenfeld Media using the code tomernews.

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