Change Blindness

Following up on last week’s entry about “normal disabilities,” I’ll say a bit about change blindness, a phenomenon that has become widely known in recent years. It may seem as if we see what’s in front of us in full detail, so that we have an essentially complete picture of the visible world. We now know this is false, thanks to the discovery that people often fail to see changes in a visual scene. Some years ago at a Toward a Science of Consciousness conference in Tucson, I sat in the audience and watched as a picture was flashed repeatedly on a big video screen. We were warned that part of the picture would change from one flash to the next, and then back again. I did not notice the change at first, but when I did the difference was dramatic. A cathedral jumped back and forth from one part of the picture to another. In another case the chimney of a house lept to the opposite end of the roof. At first, only a few people would notice these shifts, and then others would laugh and gasp as they saw what was happening.

If visual experience just copied what’s in front of us, people would notice these changes immediately, but they don’t. This has surprised many vision researchers.

Here’s another example: “Subjects are shown a video, the title of which is ‘The Color Changing Card Trick.’ They attend closely, expecting to see a color change involving the cards. One of the cards does change color. The subjects are then told that . . . there were four other color changes – one involving the color of the tablecloth upon which the cards were resting, one involving the color of the backdrop, and two involving the shirts of the experimenters. This is shocking news to nearly all subjects. When the video is played again, the color changes are obvious” (Michael Tye, Consciousness Revisited: Materialism without Phenomenal Concepts, p. 170).

This one’s just amazing. Daniel Simons and Daniel Levin “set up a kind of slapstick scenario in which an experimenter would pretend to be lost on the Cornell Campus, and would approach an unsuspecting passer-by to ask for directions. Once the passer-by started to reply, two people carrying a large door would (rudely!) walk right between the enquirer and the passer-by. During the walk through, however, the original enquirer is replaced by a different person. Only 50% of the direction-givers noticed the change. Yet the two experimenters were of different heights, wore different clothes, had very different voices, and so on” (Andy Clark, “Is Seeing All It Seems? Action, Reason and the Grand Illusion,” Journal of Consciousness Studies, December, 2002, p. 185).

In another experiment, “subjects are shown a minute long video of a static scene of a carnival carousel in which a large and exceedingly obvious foreground object (the base of the carousel) very gradually changes from red to purple. In these experiments, subjects are asked to be attentive and to watch for any changes, but for pretty much all naive subjects it is very hard to notice that the colour change is occurring” (William Seager, “Transitivity, Introspection, and Conceptuality” Journal of Consciousness Studies, November/December, 2013, pp. 47-48).

Some have tried to minimize the significance of these studies, but the surprise and even shock felt by participants shows that we have dramatically overestimated the completeness of our own conscious visual experiences.

Roger Christan Schriner


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