What we see isn’t always what’s happening (OR why demos don’t always work)

by Stephanie Chasteen on January 18, 2011

Consider this quote:

“We don’t know what we see; we see what we know.”
– Johann Wolfgang von Goethe

I’ve often wished I’d gone into cognitive science — it’s just so interesting.  (Sciencegeekgirl factoid: My undergrad degree is in social psychology.)  Instead I earn my daily (gluten-free) bread by teaching physics and can throw only glancing blows of attention towards interesting reads like Cognitive Daily and the like.  But this little set of posts came across my attention on a physics education listserv, and so I just can’t help myself.  And what really strikes my fancy is that these basic results on cognition and perception can help explain why our students don’t always see what we expect them to see in physics or other science demos.

Change blindness

Take a look at this video. Do you notice anything strange?

Here are a bunch more videos where something changes and you (or the participants) might not notice.  Watch this one where they replace a person asking for directions with another one — and many don’t notice!  This is called change blindness — basically, we’re often blind to change when there is some interruption in the scene (such as a cut in the video, or, in that one case, a door coming between you).

Here’s a great and engaging article called “Experience isn’t something we feel but something we do” which also has lots of links to different examples of change blindness.  Here’s one (mudsplashes) I took from that paper:

from http://nivea.psycho.univ-paris5.fr/ASSChtml/ASSC.html

from http://nivea.psycho.univ-paris5.fr/ASSChtml/ASSC.html

As the authors say:

The reason this is interesting is that the mudsplashes are positioned in such a way so as to not cover the change location. That way it can’t be argued that the reason you miss the change is that it is somehow masked or wiped out by any kind of superposition with flicker.

They say:

Instead of storing all the information about the outside world in the brain, we use the outside world as an external memory storage. Thus, we get the impression that we’re seeing everything there is to see in the visual field, because if we so much as faintly wonder whether we’re actually seeing something, we turn our eye (and our attention) to that thing, and it becomes available for processing.

Eye tracking studies, similarly, show that we just scan certain parts of pictures when we look at them, we’re not looking around the whole scene to really catalog the details.

So what, you may wonder.  That’s all very interesting, but does it have anything to do with teaching?  You betcha (but you knew I’d say that from the title of this post).

Perception and Demonstrations

Students don’t learn by listening to us talk at them, and this cognitive research shows that passively watching a demonstration or animation isn’t going to be that helpful either.  Students literally may not see what it is that you want them to see.

Wolf-Michael Roth has also written about that in the context of physics demonstrations:
Roth, W.-M., McRobbie, C., Lucas, K. B., & Boutonné, S. (1997). Why may students fail to learn from demonstrations? A social practice perspective on learning in physics. Journal of Research in Science Teaching, 34, 509-533.  They basically found that students didn’t have the tools to see what the teacher wanted them to see (separating the signal — the phenomena — from the noise); were confused about the relationship of the demo to other things they’d learned in physics; got confused because other demonstration or images looked similar to the demo in question; they didn’t have a chance to test their explanations of the phenomenon; and they couldn’t put the demo into a larger context.

Eric Mazur and Catherine Crouch also did a study (Am. J. Phys. 72(6), June 2004) which found that students who passively watch a demonstration don’t learn the material any better than watching a lecture on the topic (which is to say, not very well); but if students are asked to predict the outcome of the demonstration, they end up understanding it much better.  This shows the critical role of student engagement for learning.

For those of you who really want to go further into this, check out Derek Muller’s thesis, where he investigates a variety of ways to engaged students in multimedia to enhance learning.

Back to perception

I highly recommend watching this lecture from Eric Mazur (it’s an hour long, so set it up on your breakfast table and watch it over your coffee for a few mornings).  Eric is an incredibly engaging and popular speaker, and popularized the use of clickers in college classrooms.

Visualizations and Visual Illusions:  How the Mind Tricks Us.

Abstract: Neurobiology and cognitive psychology have made great progress in understanding how the mind processes information – in particular visual information. The knowledge we can gain from these fields has important implications for the presentation of visual information and student learning.

In this talk, Eric discusses how we perceive isn’t always what’s there.  When we look at the world outdoors, what we see has a range of brightness that varies over three orders of magnitude (1000X).  But because of the limitations of printing, photographs only have about 20X range of variability in brightness.  But we don’t see anything strange — we see those printed pictures as an accurate representation of the outdoor scene, even though they’re most definitely not.  That’s because the eye doesn’t see luminance; it sees reflectance, and our perception relies on contrasts in this reflectance.  Take a look at the Mazur video at 13:00-16:00 to see an amazing demonstration of this.  The brain corrects its perception based on context, like shadows.

Our cognition works like perception in some ways.  We have mental models about the world that affect what we see.  Mazur has some excellent demonstrations of this fact in that video.  Those mental models can actually override our visual memory.  Mazur likes doing demonstrations, since seeing is believing (right?).  But they don’t always work.  He has one demo showing how torque works, and that a scale registers different weights as an object is moved to the side.  But two months later, students completely misremembered the demo.  We store information by mental models, he says, not facts.  So if students don’t change their mental model, they misremember the demo.  As teachers, we have to provide the opportunity to revise that model.


Frank Noschese January 18, 2011 at 11:22 pm

I run into this quite a bit. Recently, I did a demo using colliding carts to visualize Newtons’ 3 Law.


I asked the kids to tell me which cart felt more force in the collision, based on the flexing of the metal hoops. The majority wanted to say the cart the moved faster felt more force, despite the fact that the hoops were always equally compressed. So I had to film the demo so I could show it frame-by-frame and focus their attention on the equality of the hoop size.

I have also experienced this when dropping objects of different weight. Again, the video camera is useful to show that both objects hit at the same time.

I’m having trouble viewing the Mazur video. Is that the one where he talks about textbook diagrams, eye movements when looking at pictures, and distractions?

sciencegeekgirl January 21, 2011 at 5:09 am

Hey Frank,

Nope, that’s a different talk. This one is really about perception directly, reviewing that research and how it relates to learning. I know the textbook one, that’s the one he gave at AAPT a few years back. Also a wonderful talk.


Dallas Raby February 1, 2011 at 6:16 pm

Watching the door experiment brought me back to a seminar I attended just this Saturday where the speaker conducted a little experiment. He was seeking to demonstrate that we seldom really pay attention to the people we encounter. Because of Saturday’s experiment I noticed that the pedestrian in the door video was fully engaged in giving directions, only glancing briefly at the inquirer and I was not surprised at his failure to notice the change. The identity of the inquirer was simply not important to his primary task of giving directions.

Our speaker set up his experiment by showing a famous Sherlock Holmes movie clip in which Sherlock asked Watson to look at a hat and tell him what he saw. Watson of course saw only an ordinary black bowler hat. Then Sherlock proceeded to describe the owner of the hat in detail based on observations Watson had missed.

Our speaker then formed groups of three people who had never met one another before and asked us to simply look at each other without speaking for three minutes and then tell each other everything that they had deduced about the person. We all later agreed that the deductions were remarkably accurate. What is even more remarkable is that I still have a more accurate recollection of the names, appearances and other life information about those two people that I spent five minutes with than I do for the eight people around the table that I spent four hours with.

The interesting thing about this as it relates to teaching is that we were able to quickly understand his simple instructions to observe and succeeded so spectacularly at it.

Dana Hodgdon March 18, 2012 at 10:11 pm

Can you tell me from where that Goethe quote is referenced?

Stephanie Chasteen March 18, 2012 at 11:11 pm

Sorry, it was so long ago, I don’t remember! I’d try googling it.

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