Change blindness is a perceptual phenomenon that occurs when a change in a visual stimulus is introduced and the observer does not notice it. This can happen, for example, in movies, where we tend not to notice non-central features that might change between shoots of the scene (e.g., a smashed off mirror in a car chase might be present again a few seconds later, but no one notices). In the laboratory, this is typically investigated using the flicker paradigm, where the same image (almost) is presented for brief periods, with a brief black screen in between each presentation. When this happens, peripheral features to the scene can be changed with limited notice from the participant. Important researchers who study change blindness:

Ronald Rensink, Simons & Levin, Pashler, and of course (!) William James (first!)

A cool site with examples of change blindness:

Another site of interest:

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