Yesterday, Steve of OmniBrain asked, “What is the coolest psychology experiment ever?” Feel free to provide your own answer in comments there and/or here. As for me, there are some that I think are really cool for theoretical reasons, but the coolest ever just for the sheer implausibility of the results has to be Daniel Simons and Daniel Levins’ “real-world interaction” change blindness experiment. It simply boggles the mind. First, a little bit about change blindness.
Check out this scene, and see how long it takes you to figure out what changes when the scene flashes. I’ll give you a moment.
OK, back? It might have taken you a few moments, but you probably noticed eventually that the plane’s engine, on the wing near the fuselage, disappears and then comes back in successive flashes. The difficulty people have in noticing changes like this is called change blindness. There’s a pretty large literature on change blindness, and I don’t want to get into all of that right now, because I want to get to the coolest… experiment… ever, but I will give you a few of the conclusions from the literature, from Simons and Ambinder (p. 44)1:
- “Change blindness occurs whenever attention is diverted from the change signal.”
- “Changes to objects that are central to the meaning of the scene or changes to visually distinctive objects are detected more readily than other changes, presumably because observers focus attention on important objects
- “Attention may be necessary for change detection, with changes to unattended objects going unnoticed.”
- “Attention to a changing object may not be sufficient for change detection; observers frequently fail to detect changes to the central actors in motion pictures and to real-world conversation partners even though these people clearly are attended suggesting that change detection requires observers to encode the changing features before and after the change and compare them”
In short, change blindness is an issue of attention and representation. If we fail to represent an object in a scene either before or after a change, then we won’t notice the change, and we tend not to represent objects that aren’t important to the meaning of what we’re looking at, because we’re just not paying attention to them (though paying attention to them doesn’t guarantee representation).
OK, now for the experiment. Number 4 above gives you a hint about what happened. Simons and Levin2 had experimenters approach a passer by with a map in hand (they were on the Cornell U. campus), and ask for directions to a campus building. After the passer by had been giving directions for about 15 seconds, a second and third experimenter, both carrying a door, passed between the first experimenter and the passer by. As the door went by, the first experimenter — the one who’d asked for directions — switched places with the experimenter carrying the back end of the door, who took the direction-taker’s place in front of the passer by. Here are photos from the paper, so you can see exactly what happened:
After the direction-giver finished giving directions (or just stopped), the experimenter now in the place of the direction-taker asked,
We’re doing a study as part of the psychology department [experimenter points to the psychology building next door] of the sorts of things people pay attention to in the real world. Did you notice anything unusual at all when that door passed by a minute ago?
If the direction-giver didn’t say that he or she had noticed the person to whom he was talking changed when the door passed, the experimenter then asked,
Did you notice that I’m not the same person who approached you to ask for directions?
Eight out of fifteen direction-givers failed to notice that the person they were talking to changed in mid conversation! Eight out of fifteen! Simons and Levin also noted that all seven of the people who did notice that their interlocutor had changed were students (like the experimenters were), 20-30 years old. Older participants, between 35 and 65 years old, didn’t notice the change. This led Simons and Levin to hypothesize that, if the appearance of the experimenter was relevant to the participant, they would notice the change (students are always checking out other students, ya know?), but if it wasn’t relevant (all college students look the same to me!), they didn’t notice the change.
To test this hypothesis, Simons and Levin conducted a second experiment in which the two experimenters who acted as direction-takers were dressed as construction workers, who are common on college campuses, and generally ignored by students and faculty alike. The rest of the procedure was the same (ask directions, guys with door walk in between them, experimenters switch, and so on). This time, only 4 of 12 young participants (college age) noticed the switch, supporting the hypothesis that people only notice the change when the appearance of the individuals was relevant.
At this point, you’re thinking, “This is insane! I would notice if the stranger I was talking to suddenly looked like a completely different person!” I thought the same thing, and we’re not alone. In fact, this disbelief is so common that it has its own name: change blindness blindness. In another experiment, Levin et al.3 asked participants whether they would notice changes in previously used change-blindness stimuli. In the first experiment, 83% said they would, and in the second, 64% said they would, but when asked whether other people would notice it, only 21% said they would. Both 83% and 64% are well above the percentages of people who actually noticed the changes in the stimuli (21% is closer). Thus, people consistently overestimate their ability to detect changes, but they don’t think other people are as good at change detection as they are.
1Simons, D.J., & Ambinder, M.S. (2005). Change blindness: Theory and consequences. Current Directions in Psychological Science, 14(1), 44-48.
2Simons, D.J., & Levin, D.T. (1998). Failure to detect changes to people in a real-world interaction. Psychonomic Bulletin & Review, 5, 644-649.
3Levin, D.T., Momen, N., Drivdahl, S.B., & Simons, D.J. (2000). Change blindness blindness: The metacognitive error of overestimating change-detection ability. Visual Cognition, 7, 397-412.