Memories may skew visual perception

July 21, 2011

Visual perception can be contaminated by memories of what we have recently seen, impairing our ability to properly understand and act on what we are currently seeing, researchers at Vanderbilt University have found.

The researchers used a visual illusion called “motion repulsion” to learn whether information held in working memory affects perception. This illusion is produced when two sets of moving dots are superimposed, with dots in one set moving in a different direction from those in the other set. Under these conditions, people tend to misperceive the actual directions of motion, and perceive a larger difference between the two sets of motions than actually exists.

Ordinarily this illusion is produced by having people view both sets of motion at the same time. The researchers set out to determine if the illusion would occur when one set of motions, rather than being physically present, was held in working memory.

Participants were shown a random pattern of dots and were asked to remember the direction in which the dots were moving. They were then were shown a second pattern of moving dots. They were asked to report on the direction of second dots’ movement.

The researchers found the subjects’ reports of the second dots’ movement were exaggerated and influenced by what they had previously seen. If they were first shown dots moving in one direction and later shown dots moving in a slightly counterclockwise direction relative to the first presented dots, they reported the counterclockwise movement to be more dramatic than it had actually been.

Their findings provide compelling evidence that visual working memory representations directly interact with the same neural mechanisms involved in processing basic sensory events, the researchers said.

Min-Suk Kang, et al., Visual working memory contaminates perception, Psychonomic Bulletin & Review, 2011; [DOI: 10.3758/s13423-011-0126-5]