Federico Pistono

Slashdot reports that Scientists at University College London have found the link between what we expect to see, and what our brain tells us we actually saw revealing that the context surrounding what we see is all important — sometimes overriding the evidence gathered by our eyes and even causing us to imagine things which aren't really there.

A vague background context is more influential and helps us to fill in more blanks than a bright, well-defined context. This may explain why we are prone to 'see' imaginary shapes in the shadows when the light is poor. "Illusionists have been alive to this phenomenon for years," said Professor Zhaoping. "When you see them throw a ball into the air, followed by a second ball, and then a third ball which 'magically' disappears, you wonder how they did it. In truth, there's often no third ball — it's just our brain being deceived by the context, telling us that we really did see three balls launched into the air, one after the other." The original research paper is available on PLOS, the open-access, peer-reviewed journal.

Here's the summary of the paper by Li Zhaoping and Li Jingling, Department of Computer Science, University College London, United Kingdom and Graduate Institute of Neural and Cognitive Sciences, China Medical University, Taiwan.

We study how visual perception of a target bar can be biased by contextual bars in the image, and how a Bayesian model of object inference can account for the data. Human observers are more likely to perceive a target bar when the contextual contrast, i.e., the luminance difference between the contextual bars and background, is weaker rather than stronger. Relative to the situation without the context, they are biased to perceive the target in a context of weak contrast when the target can perceptually group well with the context, as if the context fills in the target. Meanwhile, they are biased not to perceive the target in a context of strong contrast, as if the context suppresses the perception, regardless of whether it could perceptually group well with the would-be target. The Bayesian model illustrates that the context influences the perception by biasing (1) observers' prior belief that a target should be present and (2) observers' internal model of the likely input contrasts from a target bar. Our data suggest that brain areas beyond the primary visual cortex along the visual pathway are responsible for inferring object causes for input images.