Study Shows How Believing Can Be Seeing

Scientists have found the link between what we expect to see, and what our brain tells us we actually saw. The study, published February 15 in the open-access journal PLoS Computational Biology, reveals 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 that aren't really there.

Using a mathematical model, researchers Li Zhaoping and Li Jingling at University College London determined that 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.

Eighteen observers were asked to concentrate on the center of a black computer screen. Every time a buzzer sounded they pressed one of two buttons to record whether or not they had just seen a small, dim, grey "target" rectangle in the middle of the screen. It did not appear every time, but when it did appear it was displayed for just 80 milliseconds.

"People saw the target much more often if it appeared in the middle of a vertical line of similar looking, grey rectangles, compared to when it appeared in the middle of a pattern of bright, white rectangles," said Zhaoping. "They even registered 'seeing' the target when it wasn't actually there. This is because people are mentally better prepared to see something vague when the surrounding context is also vague. It made sense for them to see it - so that's what happened. When the target didn't match the expectations set by the surrounding context, they saw it much less often.

"Mathematical modelling suggests that visual inference through context is processed in the brain beyond the primary visual cortex. By starting with a relatively simple experiment such as this, where visual input can be more easily and systematically manipulated, we are gaining a better understanding of how context influences what we see. Further studies along these lines can hopefully enable us to dissect the workings behind more complex and wondrous illusions."