Change blindness is a fascinating phenomenon in which people do not notice even significant changes in an image they are viewing, as long as the change itself occurs out of view. Our visual processing is sensitive to changes that occur in view, but major changes to a scene can occur from one glance to the next without our noticing in many cases.
(See [this] color changing card trick for an example.)
One group of researchers believe they have a working hypothesis as to why our brains might have evolved in this way. Their idea is that the visual system will essentially merge images over a short period of time in order to preserve continuity – a process they call the continuity field. In essence our brains are sacrificing strict accuracy for perceived continuity.
This is in line with other evidence about how our brains work. Continuity seems to be a high priority, and our brains will happily fill in missing details, delete inconsistent details, and even completely fabricate information in order to preserve the illusion of a continuous and consistent narrative of reality.
Visual continuity is important because otherwise the world would appear jittery to us, constantly morphing as shadows play across an object, or our angle of view changes. This could be highly disruptive and distracting.
The researchers also point out that in the real world objects are fairly stable. They don’t pop in and out of existence, or morph into other objects. So not being perceptive to such changes would not be a big sacrifice and would not be likely to affect fitness. If something is actually moving or changing in our visual field we are very sensitive to that, and our attention will be drawn to it.
Neuroscientists, however, can contrive all sorts of impossible scenarios in order to probe our processing of sensory information. We did not evolve with video or photography, but researchers can use this technology to test how our brains process information.
They also give real world examples, such as the movies. There are often continuity errors in movies, missed by the vast majority of movie-goers.
Change blindness is the failure to detect non-trivial changes in the visual field. The failure to see things changing right before your eyes may seem like a design fault, but it is actually a sign of evolutionary efficiency.
The term ‘change blindness’ was introduced by Ronald Rensink in 1997, although research in this area had been going on for many years. Experiments have shown that dramatic changes in the visual field often go unnoticed whether they are brought in gradually, flickered in and out, or abruptly brought in and out at various time intervals. The implication seems to be that the brain requires few details for our visual representations; the brain doesn’t store dozens of details to which it can compare changes (Simons and Levin: 1998). The brain is not a video recorder and it is not constantly processing all the sense data available to it but is inattentive to much of that data, at least on a conscious level.
Change detection in films is notoriously poor when the change occurs during a cut or pan, as demonstrated by the color-changing card trick video and a number of other videos where a different actor appears after a cut, without the change being noticed by most viewers. Some experiments have shown that a person may be talking to someone (behind a counter, for example) who leaves (bends down behind the counter or exits the room) and is replaced by a different person, without the change being noticed.
Apparently, change blindness is due to the efficient nature of our evolved visual processing system, but it also opens the door to being deceived, much to the delight of magicians and sleight-of-hand con artists.
More examples of change blindness:
- Change Blindess (farisyakob.typepad.com)
- Did You Not Notice or Not Remember? (theness.com)
- Another Cool Change Blindness Video: The Color Changing Card Trick (capitalogix.typepad.com)
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