The Cost of Task Switching: A Simple Yet Very Powerful Demonstration

The Cost of Task Switching: A Simple Yet Very Powerful Demonstration

By Yana Weinstein

As a cognitive psychologist, I think it’s important for students to understand how their attention works. But, unlike aspects principles of cognition that are easy to demonstrate, attention can be somewhat elusive. Perception can be demonstrated with mind-blowing visual illusions such as apparent motion (1) and color adaption (2). (For additional visual illusions, see websites like this one.)

Image by Aaron Fulkerson on Flickr  (CC BY-SA 2.0)

Image by Aaron Fulkerson on Flickr (CC BY-SA 2.0)

And, the vagaries of memory can be demonstrated by getting students to memorize a list of words (3), asking them to recall it, and observing that most students will recall a word that wasn’t on the list. For example, if you get students to study the words bed, rest, awake, tired, dream, wake, snooze, blanket, doze, slumber, snore, nap, peace, yawn, and drowsy, 80% of them will remember seeing the word sleep as well.

Image from a 2009 presentation by Henry L. Roediger

Image from a 2009 presentation by Henry L. Roediger

But attention is so hard to pin down, that even certain contemporary researchers have thrown up their hands and decided that perhaps attention as it’s currently defined cannot be studied (4). Nevertheless, most cognitive psychologists do agree that attention is an important concept to teach their students. One important aspect of attention is the idea that going back and forth between two different tasks involves switch costs that decrease efficiency and slow down reaction speeds in both tasks (5).

Image from  Interleaving poster  designed by Oliver Caviglioli

Image from Interleaving poster designed by Oliver Caviglioli

In this blog post, I’m going to describe a very simple yet powerful demonstration of task switching costs. This is a demonstration that students can take part in alone, in pairs, in groups of three, or as a class with one student volunteering to be the “case study” that the rest of the class observes. In this demonstration, students are invited to time themselves performing two separate tasks, and then attempting to switch back and forth between the two tasks.

The Demonstration

The demonstration involves doing three very short tasks:

  • Task 1 is counting up from 1 to 26.

  • Task 2 is reciting the alphabet from A to Z.

  • Task 3 is interleaving numbers with letters, 1-A-2-B-3-C etc. – that is, switching back and forth between Tasks 1 and 2.

Yep, that’s it!

Independent Activity

If you want students to do it on their own – or you, the reader, want to try it out for yourself – they can simply do each of the three tasks, and time themselves completing each one. Try it right now – before you read the rest of the post!

Image from Pixabay

Image from Pixabay

How long did each of the three tasks take you to complete? I had 27 students in my online class complete the three tasks alone and tell me the time it took them to complete each task (in seconds) as part of a weekly quiz. Here were the results:

  • Task 1 (counting from 1 to 26) took 5-48 seconds
  • Task 2 (reciting the alphabet) took 3-22 seconds
  • Task 3 (switching back and forth) took 27-110 seconds.

Importantly, every single student took longer to complete the combined Task 3 than the sum of the time it took them to complete both of the other tasks (Task 1 + Task 2). So, every student in my sample experienced task switching costs.


Classroom Activity

If you want to use the demonstration as used as a classroom activity, you can try out the following versions of the activity:

  • Pairs, where one student acts as timer and the other as the participant (activity time = 5 minutes);
  • Pairs, where students take turns to act as timer and participant (activity time = 10 minutes; good for smaller groups to generate sufficient data)
  • Groups of three, where each person in the trio takes on one of the three tasks (activity time = 5 minutes; good for larger groups to demonstrate a between-subjects design, but note that differences between students might make the task switching effect less easy to detect if each student only does one of the tasks).
  • An alternative version that does not require students breaking out into groups is to ask one volunteer to demonstrate all three tasks in front of the class. Since task switching costs in this paradigm are so robust, even a single participant case-study can serve to demonstrate the effect.


(1) Wertheimer, G., 1912. Experimentelle Studien ueber das Sehen von Bewegungen. Zeitschrift fuer Psychologie, 61, 161265.

(2) Winkler, P., McDermott, K. C., Caplovitz, G., & Webster, M. (2011). Figural chasers. Journal of Vision11, 1014-1014.

(3) Roediger, H. L., & McDermott, K. B. (1995). Creating false memories: Remembering words not presented in lists. Journal of Experimental Psychology: Learning, Memory and Cognition, 21, 803-814.

(4) Anderson, B. (2011). There is no such thing as attention. Frontiers in Psychology2.

(5) Gopher, D., Armony, L., & Greenshpan, Y. (2000). Switching tasks and attention policies. Journal of Experimental Psychology: General129, 308-339.