How You Feel the World Impacts How You See It

April 3, 2009,
Piezoelectric tactile stimulator. Courtesy Jerome Pasquero, McGill University

In the classic waterfall illusion, if you stare at the downward motion of a waterfall for some period of time, stationary objects -- like rocks -- appear to drift upward. MIT neuroscientists have found that this phenomenon, called motion aftereffect, occurs not only in our visual perception but also in our tactile perception, and that these senses actually influence one another. Put another way, how you feel the world can actually change how you see it -- and vice versa.

In a paper published in the April 9 online issue of , researchers found that people who were exposed to visual motion in a given direction perceived tactile motion in the opposite direction. Conversely, tactile motion in one direction gave rise to the illusion of visual motion in the opposite direction.

"Our discovery suggests that the sensory processing of visual and tactile motion use overlapping neural circuits," explained Christopher Moore of the McGovern Institute for Brain Research at MIT and senior author of the paper. "The way something looks or feels can be influenced by a stimulus in the other sensory modality."

Volunteers watched visual motion on a computer screen while placing their right index fingertip on a tactile stimulator directly behind the screen. The stimulator consisted of a centimeter-square array composed of 60 pins to deliver precisely controlled vibrations to the fingertips. This stimulator, the only one of its kind in the world, was developed by Qi Wang of Georgia Institute of Technology and Vincent Hayward of Université Pierre et Marie Curie in France.

To test the effect of visual motion on the subjects’ perception of touch, the monitor displayed a pattern of horizontal stripes moving upward or downward for ten seconds. After this visual pattern had disappeared, a single row of horizontal pins simultaneously vibrated the subjects’ fingertips. Although the pins delivered a static burst of vibration, all eight subjects perceived that the row of pins was sweeping either upward or downward, in the direction opposite to the movement of the preceding visual pattern.

To test the effect of tactile motion on visual perception, adjacent rows of pins vibrated in rapid succession, creating the sensation of a tactile object sweeping up or down the subjects’ fingertips. After 10 seconds of this stimulus, the monitor displayed a static pattern of horizontal stripes. Contrary to the prevailing assumption that vision always trumps touch, subjects perceived the stripes as moving in the opposite direction to the moving tactile stimulus.

[Click here to view demos of the motion stimuli used in this study: http://web.mit.edu/~tkonkle/www/CrossmodalMAE.html]

"Aftereffects were once thought to reflect fatigue in the brain circuits," said Konkle, "but we now know that pools of neurons are continuously coding motion information and recalibrating the brain to its sensory environment. Our neurons are not tired, they are constantly adapting to the world around us."

Recent studies have found that a region of the visual cortex known as MT or V5 -- long thought to play a major role in the perception of motion -- may also process tactile motion. Moore’s team intends to explore this brain region in future studies to determine whether it contributes to these cross-modal motion aftereffects. "Neuroscientists study perceptual illusions because they help reveal how the brain gives rise to conscious experience," Moore said. "We don’t experience the world through isolated senses, and our data support the emerging view that the brain is organized for cross talk among different sensory modalities."

Provided by Massachusetts Institute of Technology (news : web)

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superhuman
4.5 / 5 (2) Apr 03, 2009
"Our discovery suggests that the sensory processing of visual and tactile motion use overlapping neural circuits,"


It suggests that there is a dedicated circuit which corrects perception for the movement of the world relative to the observer and that this circuit takes advantage of all the sensual input.

This circuitry needs some time to readjust after prolonged exposure to one type of movement, since such situations almost never happen in nature there was no need to optimize for this case.

Contrary to the prevailing assumption that vision always trumps touch, subjects perceived the stripes as moving in the opposite direction to the moving tactile stimulus.


Subjects' perceived frame of reference was still moving in the direction of the first stimulus so the second stationary stimulus seemed moving in the other direction, the effect is not due to conflict between the senses but rather due to conflict between perceived movement of the world relative to the observer and the actual movement, notice that if the movement of the first stimulus was truly due to the fact that the surrounding was moving in relation to the observer then the interpretation of the second stimulus would be correct.

"We don't experience the world through isolated senses, and our data support the emerging view that the brain is organized for cross talk among different sensory modalities."


Not for cross talk but for synthesis and it's rather obvious since we don't perceive 5 separate worlds.

The brain combines all the sensual information into one coherent picture of reality, this picture is then analyzed and at this stage it no longer matters which sense supplied which part of it.

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