Visual perception is generally accurate and stable. However, when a visual stimulus provides conflicting or insufficient information, perception can be bi-stable or even multi-stable - that is, the way an image is perceived by the viewer can change or switch back and forth over time. By studying the visual system's solution when faced with such ambiguous conditions, Dr. Xiangchuan Chen from the University of Science and Technology of China and Dr. Sheng He from the University of Minnesota sought to tease out clues to the underlying mechanisms of visual perception.
Earlier research had shown that perception can be stabilized when the ambiguous visual stimuli were presented intermittently. Memory of the recent perceptual experience had been proposed to explain this stabilization effect. But the nature of this "perceptual memory" has remained unclear.
In the new work, Drs. Chen and He showed that the mechanism responsible for perceptual stabilization was independent of the memory of object identity, including various qualities possessed by an object, such as color. Using a rotating cylinder image that prompts bi-stable perception, they showed that changing the color, the moving speed of the dots on the cylinder, the size, or the stereo depth of the cylinder had no or minimal effect on the perceptual stabilization of the rotating cylinder. In contrast, stabilization depended on the stimulus location - where in the visual field the object fell.
In a second set of tests, ambiguity in the presented image stemmed from each eye being presented with a different image. In this test, two different patterns were intermittently presented separately to the two eyes and were swapped between the two eyes synchronously with the intermittent presentation. The researchers found that perceptual stablization did not appear to be based on the memory or representation of the stimulus itself; instead, it was based on perception being stabilized to one eye rather than the other.
Together, the findings from both experiments are consistent with the view that the possible mechanism underlying perceptual stabilization is not the memory of a stimulus, but rather the removal of so-called local adaptation.
Xiangchuan Chen and Sheng He: "Local factors determine the stabilization of monocular ambiguous and binocular rivalry stimuli"
Published in Current Biology, Volume 14, Number 11, 8 June 2004.