Ever notice a blank wall where a painting used to be, only to find out it had been gone for days? That’s change blindess at work. As we go about our business, our visual scene is changing frequently. We think that we have a clear and accurate view of the world as we move around it; but we’re actually not that great at detecting changes in our visual environment. This is going on all the time – things in your environment change, but you’re none the wiser.
This even applies to changes that you would think were completely obvious. The classic study on change blindness had a researcher ask participants for help with some written directions. While they were talking, a brief distraction was arranged, during which a confederate switched places with the researcher, and continue the conversation. Amazingly, most of the participants did not even notice the switch, and carried on talking to the completely different person! (1) Here’s a video of a similar study, reporting that 75% of people didn’t notice!
How is change blindness explained?
There is still work to be done in this area, but the main theory is based on the idea of mental maps of scenes, which are stored in long-term memory. (2) When we fixate our attention on a particular aspect of our visual environment, it gets added to the mental map. These representations are thought to be fairly detailed, though not wholly accurate, and they stay for some time after they’re formed. Unless a particular aspect of a scene has been indexed in the mental map, there’s nothing to compare it with to realise there has been a change. So the most important factor in change blindness is not memory, but attention. If something hasn’t been fixated on, according to this theory, it doesn’t get added to the map, and changes to it (or its disappearance) won’t be noticed.
Where to go for more information on change blindness
For general interest, the You Tube clip linked to above is worth watching, but for academic interest get Hollingworth and Henderson’s 2002 paper (it’s on Andrew Hollingworth’s website for free download), also look up Rensink’s work.
(1) Simons, D. J. & Levin, D. T. (1998). Failure to detect changes to people during a real-world interaction, Psychonomic Bulletin and Review, 5, 644–649
(2) Hollingworth, A., & Henderson, J. M. (2002). Accurate visual memory for previously attended objects in natural scenes. Journal of Experimental Psychology: Human Perception and Performance, 28, 113-136.