Magic in the Classroom Example Lesson Idea: Change Blindness & Metacognition

The following lesson idea is an example of some of my own work applying magic to classroom settings. If you have your own idea you’d like to share please do get in touch!

This presentation can slot nicely into lesson on introductory psychology, cognitive psychology, sensation & perception, etc. It’s fairly easy to tune the details so as to make this suitable for audiences ranging from the general public through grad students, depending on how detailed you want to go with the research methodology. The video above is a recording of me performing for a general audience at Hjärndagen (Brain Day) in Stockholm in 2023.

Outline of the presentation:

(optional)* Performance of The Princess Card Trick using physical cards for a single audience member
Performance of the onscreen card trick for the entire audience
Introduce the concept of change blindness
Demonstrate the flicker paradigm for the audience on screen
- Start with a series of single changes
- Finish with an images featuring multiple changes
Discussion points can include:
- Change Blindness
- Metacognition (e.g. Change Blindness Blindness)
- Relation between magic effects and psychological research (similarities and contrasts)
- Satisfaction Search
- Feature Binding, Attention, and Illusory Conjunctions
- Reconstructive Memory

The idea is use performance magic to provide an interactive demonstration of change blindness phenomena.

I like to start by performing a version of the Princess Card Trick. There are *many* ways to perform this, but arguably the first published version(s) appear in T Nelson Down’s The Art of Magic, which was published in 1909 (many more details below, if you’d like them). I like to open with a slight-of-hand version, using actual playing cards, but this step is entirely optional, if you’re not comfortable performing the trick, or if you just want to expedite the presentation.

A nice thing about the Princess Card Trick is that it can be easily be adapted to a screen-based presentation. I have an animated powerpoint version, that you can download here, but even just a sequence of still images should be sufficient. I use four face cards, but you’re also not necessarily limited to faces or even to just four. All you need is two arrays consisting of all different playing cards, where the second array is visually similar, and one card less than, the first. In presentation, be sure to emphasize to the audience that they should select one card, hold it in their mind, etc. As this helps increase the odds that they’ll fail to remember the other cards or notice when they all change. (You can later call back to the exact words of your script, and their intended purpose, if you want to integrate reconstructive memory into the discussion).

The card effect is a nice way of quickly engaging attention, and you can then explain that the trick operates based on a psychological principle known as ‘change blindness.’ Psychologists didn’t discover this phenomena with playing cards, but rather with pictures- through a method called ‘The Flicker Paradigm’. (Depending on the crowd, there’s a discussion to be had around the fact that the card trick pre-dates the formal psychological concept by nearly 100 years- this isn’t to say that magicians mechanistically understood how/why the illusion worked, but they absolutely did know how to robustly reproduce the effect).

I then move on to the flicker paradigm demonstration. The flicker paradigm demos are effectively just animated gifs with four frames- A picture, a blank screen, a second modified picture, and another blank screen. Explain that the key outcome of the experiment is a reaction time measure. Participants simply indicate (originally with a button press) when they have detected the discrepancy between the two pictures frames. Ask the audience to all raise their hands into the air, and tell them to drop their hands when they detect the change. (This is a minor thing, but I find that getting people, particularly students, to do this, rather than putting their hands up when they see the change increases their engagement/participation).

It’s quite easy to make your own demo gifs with your own photographs and Powerpoint. Use any photo editing software (e.g. Photoshop or Gimp) to create your modified images, and then create a powerpoint slide show that’s four slides long (you can download a template here). The first slide is the first unmodified picture, the second slide is a blank, the third slide is the modified picture, and the fourth slide is another blank. Make sure your two pictures are aligned identically. Then, in Powerpoint’s menu, go to File -> Export. In export you should see an option to select a file format. Select ‘Animated Gif’ from the menu. Then on the next pop-up, you’ll see several options. Set the ‘Seconds Between Slides’ option to 0.5 seconds. Then hit ‘Export,’ and you’ve got a Flicker-style demonstration gif that can be easily embedded into various bits of media. As you can see (e.g. 4:22 in the video), I also add indicator shapes to the Powerpoint slides to highlight the changes. Just embed the gif in the Powerpoint, select Insert -> Shape -> Oval (/arrow or whatever). Then position/format the shape in front of the .gif to highlight the change, and then animate it to ‘appear on click.’ This is a bit of overkill for the the single changes, but provides two benefits. First, it gives you a nice beat where you can take the indicator away to show how, ‘when you know what to look for, the change feels extremely obvious.’ Second it sets you up nicely for the final slide with the multiple changes.

After three or so examples of single changes, explain that you will do one more. I usually make a comment on how the audience is ‘warmed up’ so they might be faster this time. For this final slide, I make a demo with multiple changes (sky’s the limit, but I usually aim for around 20+ manipulations). If you go through the hand raising/dropping procedure again, people will be much quicker (because there are more changes to see). But they’ll probably stop looking as soon as they’ve spotted one change (nice tie-in to the concept of ‘satisfaction search’). After most of the hands have dropped, I say something along the lines of “That was much quicker! Now if we wanted to I could say: ’Everyone put your hands back up, and drop them when you get all 50 changes [or whatever number you’ve added]’.” Then you can advance the slide to indicate all the changes that were happening simultaneously. This can lead to a nice discussion of metacognitive evaluations, perceptual and memory illusions, and more specifically the idea of ‘change blindness blindness’

Key References:

Downs, T. N. (1909). The Art of Magic. (J. N. Hilliard, Ed.). Chicago, IL: Arthur P. Felsman. https://archive.org/details/cu31924084451008/page/n87/mode/2up?q=princess+card

Levin, D. T., Momen, N., Drivdahl IV, S. B., & Simons, D. J. (2000). Change blindness blindness: The metacognitive error of overestimating change-detection ability. Visual Cognition, 7(1-3), 397-412

Simons, D. J., & Rensink, R. A. (2005). Change blindness: Past, present, and future. Trends in cognitive sciences, 9(1), 16-20.

Rensink, R. A. (2018). To have seen or not to have seen: a look at Rensink, O’Regan, and Clark (1997). Perspectives on Psychological Science, 13(2), 230-235.

Rensink, R. A., O'Regan, J. K., & Clark, J. J. (1997). To see or not to see: The need for attention to perceive changes in scenes. Psychological science, 8(5), 368-373.

Treisman, A., & Schmidt, H. (1982). Illusory conjunctions in the perception of objects. Cognitive psychology, 14(1), 107-141.

*Quick Addendum re the card trick itself: The magic portion of the demonstration is based on Henry Hardin’s ‘Princess Card Trick’. The trick’s explanation can be found in T Nelson Down’s The Art of Magic (1909), and it shows up even earlier via advertisements in Mahatma magazine as ‘The Prince’s Card Trick’ (the fact that it’s now known as the Princess card trick is probably due to a typographical error- Hardin aka EA Parson’s would often promote himself as ‘The Prince of Ideas’). There are many ways of accomplishing this effect with gaffed and ungaffed cards. The version I use in the above video is based on handling by Jay Sankey that he calls ‘The Usual Suspects’. In the past, I’ve performed versions based-on Eugene Burger’s handling of ‘Limited Edition’.