| The test participants had a house projected on one eye and a face on the other eye. This triggered an alternating perception, since the brain could not reconcile the two pictures with each other.
Image: Max Planck Institute for Biological Cybernetics
We do not consciously perceive everything around us, even if it falls into our field of vision. The overwhelming abundance of information forces our brain to focus on a few important things; our perception is an ongoing process of selecting, grouping and interpreting visual information. Even though we have two eyes, our brain combines the two impressions. Experts call this binocular vision. Yet, if conflicting information is presented to the eyes, only the input to one eye is perceived at a time, while the other is suppressed. Our perception changes at specific intervals between the two images - a phenomenon called "binocular rivalry". This process occurs automatically without voluntary control.
The scientists, Natalia Zaretskaya, Axel Thielscher, Nikos Logothetis and Andreas Bartels demonstrated that the frequency at which alternations between the visual information occurred could be experimentally reduced: Two different stimuli, a house and a face, were projected into the right and left eyes, respectively, of 15 experimental subjects. Since the brain could not match the pictures, alternations in perception occurred. When the scientists temporarily applied an alternating magnetic field to the subjects' posterior parietal cortex, a higher-order area of the brain, the perception of each individual image was prolonged.
"Our findings suggest that the parietal cortex is causally involved in selecting the information that is consciously perceived," explains Natalia Zaretskaya, a Ph.D. student involved in the project. "It also demonstrates the important role of this area in visual awareness."
"Understanding the neural circuits underlying the percepts and their switches might give us some insight into how consciousness is implemented in the brain, or at least into the dynamic processes underlying it", explains Andreas Bartels, scientist at the CIN.
Natalia Zaretskaya, Axel Thielscher, Nikos K. Logothetis, Andreas Bartels
Disrupting parietal function prolongs dominance durations in binocular rivalry
Current Biology (2010); doi: 10.1016/j.cub.2010.10.046
Source: Max Planck Institute