Washington, April 10 (ANI): Ever wondered why do stationary rocks appear to drift upwards while staring at the downward motion of a waterfall? Well, new research has shown that motion in one direction gives 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," said 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," he added.
During the study, the subjects 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 centimetre-square array composed of 60 pins to deliver precisely controlled vibrations to the fingertips.
For testing the effect of visual motion on the subjects' perception of touch, the monitor displayed a pattern of horizontal stripes moving upward or downward for 10 seconds.
A single row of horizontal pins simultaneously vibrated the subjects' fingertips after the visual pattern had disappeared.
Despite the fact that the pins were delivering 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.
The monitor displayed a static pattern of horizontal stripes after 10 seconds of that stimulus, and the subjects were found to perceive the stripes as moving in the opposite direction to the moving tactile stimulus.
That finding was contrary to the prevailing assumption that vision always trumps touch.
"Aftereffects were once thought to reflect fatigue in the brain circuits, 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," said Konkle.
Moore says that studies conducted in the recent past have suggested that a region of the visual cortex called MT or V5, long thought to play a major role in the perception of motion, may also process tactile motion.
The researcher is planning 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. 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," Moore said.
The study has been published in the online issue of the journal Current Biology. (ANI)