February 12, 2004
Brain Has Separate Areas For Actual And Interpreted Sensory Data

But we decide what is right and which is an illusion.

But a new collaborative study involving a biomedical engineer at Washington University in St. Louis and neurobiologists at the University of Pittsburgh shows that sometimes you can't believe anything that you see. More importantly, the researchers have identified areas of the brain where what we're actually doing (reality) and what we think we're doing (illusion, or perception) are processed.

Daniel Moran, Ph.D., Washington University assistant professor of biomedical engineering and neurobiology, and University of Pittsburgh colleagues Andrew B. Schwartz, Ph.D., and G. Anthony Reina, M.D., focused on studying perception and playing visual tricks on macaque monkeys and some human subjects. They created a virtual reality video game to trick the monkeys into thinking that they were tracing ellipses with their hands, though they actually were moving their hands in a circle.

They monitored nerve cells in the monkeys enabling them to see what areas of the brain represented the circle and which areas represented the ellipse. They found that the primary motor cortex represented the actual movement while the signals from cells in a neighboring area, called the ventral premotor cortex, were generating elliptical shapes.

The mind has the capability to create an interpreting facility to map between what it sees and how it perceives what it sees. This allows the mind to adjust for the effects of bifocals and other sense-distorting factors. While this capability is adaptive it can sometimes be tricked into creating erroneous interpretations of sensory input.

The research shows how the mind creates its sense of order in the world and then adjusts on the fly to eliminate distortions.

For instance, the first time you don a new pair of bifocals, there is a difference in what you perceive visually and what your hand does when you go to reach for something. With time, though, the brain adjusts so that vision and action become one. The ventral premotor complex plays a major role in that process.

Knowing how the brain works to distinguish between action and perception will enhance efforts to build biomedical devices that can control artificial limbs, some day enabling the disabled to move a prosthetic arm or leg by thinking about it.

Results were published in the Jan. 16, 2004 issue of Science.

"Previous studies have explored when things are perceived during an illusion, but this is the first study to show what is being perceived instead of when it is happening," said Moran. "People didn't know how it was encoded. And we also find that the brain areas involved are right next to each other."

Think back to childhood. We all had to learn to judge the distance of our hands from our faces by how the hands became smaller and the angles of the arms showed the hands changing position. We now all make those interpretations and many similar interpretations of raw sense material quite subconsciously. But we need the ability to change those interpretations as we grow older and our senses decline or because we encounter new environments which create new patterns of sensory input.

Share |      Randall Parker, 2004 February 12 03:44 PM  Brain Memory

Wes Ulm said at February 15, 2004 11:52 PM:

This is analogous to those old-fashioned visual processing tests where a person is shown a deceptive picture (like the classic candlestick-in-white surrounded by an apparent image of a kissing couple in black, or a group of diagonal lines for which there appear to be more than there actually are), then asked to interpret it. Stephen Kosslyn up here at Harvard is involved with this work an awful lot.

Basically, the separation of perception and processing is *evolutionary advantageous* apparently, since this allows the brain to instantly recognize and act upon meaningful patterns rather than raw visual data. (Awfully useful to take one glance and see that hungry saber-toothed tiger in an instant.) Of course, the flip side is that the "mind's eye" may often diverge from the actual eye in terms of what's reported.

This is an interesting field b/c of its applications to criminal justice, among other areas. Eyewitness testimony generally requires specific information about tiny minutiae observed under high pressure, and the brain does an awful lot of filtering under such circumstances. This is why culprits are often misidentified, or why a witness's initial impression differs from the criminal as seen later. This IIRC is why the cops work so hard to obtain corroborating details (suspect's location at particular place and time) as well as physical evidence, since it's sometimes so tough to be certain that the witness's perception under the circumstances was accurate.

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