Change Blindness

Notes for revision

Recast this and other exercises in more of an exploratory (less didactic) way. It could unfold like GameBug does, with links to reveal the next step. For example, start with one example, then go on to the full set. Finally, give the change-detector explanation. Add more references. Write an instructor’s supplement. Could this be made more configurable? It is probably impossible to let users place their own images without uploading them to a server. Not necessarily: see CVD demos and afterimage. Would it be worth adding a reaction-timer in order to see which are hardest? There is no obvious graph to make with such data.
Simons and Levin (1997) video
Levin et al. (2002) video

Notes

Daniel Levin’s lab studies real-world examples of change blindness. For example, a person is unaware when his conversation partner switches in mid-interaction (Simons and Levin, 1997; video), or a photographer is unaware when his subject switches (Levin et al., 2002; video). Magic and sleight-of-hand are also good examples of change-blindness or misdirected attention.

Experiment

Our attention is usually drawn to changes in the environment, so noticing an abrupt alteration in a photograph should be easy. However, some conditions can make this task difficult. Try the first 10 examples in

, showing photographs. You probably found some of them hard and some of them easy. Once you noticed the alteration, even with the flicker, it probably became impossible not to see the changes. They seem to pop out of the image at you. Even in the hardest ones, removing the flicker made the task trivial. Now try the last 10 examples in

, showing abstract scenes. Were those more difficult?

Explanation

Research starting in the 1970s has shown that someone paying close attention to one event or object may not notice odd happenings outside the area of attention. This has been termed inattentional blindness, failure to see unattended items. In contrast, change blindness is failure to see changes to an image when the change occurs along with a brief eye movement or flash in the image. Unlike inattentional blindness, change blindness persists when one is actively looking for a change. The relationship between these two phenomena is still not clear and both are subjects of current research.

As you saw in the demonstrations, it is easy to see changes when they occur without a flash and much more difficult when the flash is present. In fact, the flash need not even obscure the area of change. It needs only to distract. Normally, the visual system automatically directs attention to change, using local motion cues in the visual field. However, when a blank field is inserted between images, that flicker may overwhelm the mechanisms that respond to local motion. Lacking that automatic control, you must instead direct your attention by slower high-level mechanisms. You search the scene systematically until you happen to hit the area that is changing.

Further Exploration

Once you noticed a change, it was impossible not to see it. How long does that last? Come back to these demonstrations in a few hours, then a few days, and then a couple of weeks. Each time, test yourself on a different example. (You should now make note of the examples that were most difficult and use them for your later tests.)
Try these demonstrations on several friends and make note of how long it takes to see each change (the timer on a digital watch or the second hand of a clock will be accurate enough). (A) How much variation is there within the group you tested? (B) Does everyone find the same examples difficult?

Questions

Can you make any generalizations about features of the image or the nature of the change that make the task more or less difficult?
Where, outside an experimental setting, might change blindness occur?
When looking for changes in
, did your search seem more like a serial search or a parallel search (see )? What type of search is it when the black flash is removed?

References

Rensink RA, O’Regan JK, Clark JJ (1997). To see or not to see: The need for attention to perceive changes in scenes. Psychological Science 8:368-373. []
Rensink RA, O’Regan JK, Clark JJ (2000). On the failure to detect changes in scenes across brief interruptions. Visual Cognition 7:127-145. []
Simons DJ, Levin DT (1997). Change Blindness. Trends in Cognitive Sciences 1:261-267. [doi]
Simons DJ, Levin DT (1998). Failure to detect changes to people during a real-world interaction. Psychonomic Bulletin and Review 5:644-649. [doi]
Levin DT, Simons DJ, Angelone BL, Chabris CF (2002). Memory for centrally attended changing objects in an incidental real-world change detection paradigm. British Journal of Psychology 93:289-302. [doi]