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Why the brain perceives only limited information

Teresa Tanoos's picture
Scientists pinpoint major difference in conscious and unconscious motion in the brain.

Everyday our brains are being bombarded with all sorts of images and information, but only a small portion is absorbed into our consciousness, while the rest goes floating somewhere in the background.

How the brain chooses which information to retain in consciousness, and which gets stored in the deeper recesses of the mind, is a question scientists have been trying to figure out for a long time – and, now, a research team from Germany appears to have found some answers.

According to a recent study, published in the journal Current Biology, volunteers participated in an illusory visual process known as "binocular rivalry". During the process, two different images were presented to each of the participant's individual eyes, which allowed the researchers to identify a major difference between conscious and unconscious motion within the brain.

This process of “binocular rivalry” essentially renders our brains incapable of choosing which image to retain because they are constantly shifting every few seconds as they enter into and out of consciousness. In other words, the images we see are perceived as "rivals" competing for our attention – taking turns as they go in and out of our conscious mind.

Eleven participants took place in the study, each of whom was shown a different image for each eye, with one image moving while the other did not. Simultaneously, an infrared eye tracker monitored their eye movements.

During the process, magnetic pulses were simultaneously administered to disrupt the region of the brain associated with visual motion.

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As a result, the researchers found that the magnetic pulses used to stimulate the portion of the brain where visual motion took place, did not have any effect on the length of time the moving image was perceived, although the participants did perceive the non-moving image for a greater length of time.

The researchers did not anticipate this result, but they report that the magnetic pulses administered to the participants’ while they were unconsciously processing motion triggered a reaction that caused their minds to take longer to become conscious of the moving image. But as soon as the participants became conscious of the moving image, the magnetic pulses no longer had any effect.

The researchers therefore concluded from these findings that there appears to be a “substantial qualitative difference” between the conscious and unconscious perception of motion.

The team added that magnetic pulses administered to the brain could weaken a suppressed image, therefore postponing how long it takes to enter back into consciousness. But once that happens, the researchers explain that the cycle becomes more difficult to disrupt.

In other words, unconscious motion can make it harder to compete with a non-moving image because the latter is more prone to disruption, whereas images in motion seem to become increasingly resilient against disruption as soon as the image in motion enters consciousness.

The research team from Germany admits that additional research is needed in order to learn more about this process and what’s behind it. They cite numerous possible reasons, ranging from changes in neural noise to adaptation.

SOURCE: Current Biology, Perceptual effects of stimulating V5/hMT+ during binocular rivalry are state specific, doi:10.1016/j.cub.2013.09.002, Natalia Zaretskaya, Andreas Bartels, published October 21, 2013.