How Visual Illusions Make Your Brain Flip [Brain]

It’s on oversize skull. No, wait, it’s two people under an arch. Hold on, it’s a skull again. Two very different images shall be perceived in this trick picture and now we are one step toward understanding how the brain spontaneously flips between such views, with the discovery of what could be the relevant brain region.

The precise neural mechanism that provokes the brain to change its view of a scene is unknown, but it surely is believed to play a huge role in perception by acting as a kind of reality check, says Ryota Kanai of University College London. ” We want a trigger to prompt possible different interpretations so that we don’t get stuck with a potentially incorrect interpretation of the realm.”

To find out which portion of the brain is likely to be involved, Kanai and co-workers asked 52 volunteers to observe a video of a revolving sphere and press a button when the rotation of the field seemed to change direction. Crucially, the field was not changing direction; it can simply be looked as if it would be rotating in either direction. How long each rotation-direction was perceived for was recorded and a median ” switch rate” assigned to all the volunteers.

The team then used structural magnetic resonance imaging to look for active brain regions during this task. This pointed to the superior parietal lobes (SPL), two areas towards the back of the pinnacle known to manipulate attention and process three-dimensional images. People whose cortex was thicker and better connected in this region had faster switch rates.

To test whether or not the SPL had a task in triggering the switch, the researchers stimulated each lobe with a magnetic field – effectively knocking out the function of that lobe – while the volunteers rewatched the field illusion. The team found that the switch rate slowed when either lobe was exposed to the magnetic field (Current Biology, DOI: 10.1016/j.cub.2010.07.027 ).

” One possibility is that the SPL is really triggering the perceptual switches by sending a signal to ‘reset’ the appearance,” says Kanai. ” Or it can be that folks with an enormous SPL are better at noticing other possible interpretations for the ambiguous sphere, which would also induce a faster switch rate.”

Andrew Parker at the University of Oxford reckons the work is intriguing but adds that there is more to be done to verify that the region is directly all for provoking these perceptual changes.

Image: Mary Evans Picture Library

New Scientist reports, explores and interprets the consequences of human endeavour set inside the context of society and culture, providing comprehensive coverage of science and technology news.

Source

This post is tagged: current biology, incorrect interpretation, magnetic resonance imaging, neural mechanism, rotation direction, three dimensional images, university college london