"Mud Splashes" Render Picture Changes Invisible
J.K. O'Regan, R.A. Rensink, J.J. Clark, Cambridge Basic Research, Cambridge, MA, USA.

Investigative Ophthalmology & Visual Science, 37:213. 1996. [ARVO 1996; Ft. Lauderdale, FL.]

Purpose. To establish that changes in natural scenes are detected when they produce transients that attract attention to the location of the change. Change detection is impaired when other, unrelated transients occur at the same time.

Methods. Observers were shown pictures of natural scenes in which a prominent object changes color, position, or presence/absence repetitively every 6.2 seconds and were asked to press a button as soon as they saw the change. Each time the picture changed, six small shapes (ovals or squares about 1/10th the picture width in size) were briefly (80 ms) spattered on the picture like mud splashes on a car windshield. The splashes did not obscure the change.

Results. Without the mud splashes, picture changes were immediately detected. With the mud splashes, observers took several transitions, and sometimes much longer, to detect the change. The ability to detect the change depends strongly on whether it involves the "center of interest" of the picture, as defined operationally in a prior control experiment.

Conclusions. The results suggest that essentially only the "center of interest" of a picture is encoded in memory. The impression of continuously seeing "all" of a visual scene may be an illusion deriving from the fact that any change usually creates a visual transient that attracts attention to the changing location.

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