Haptics Impacts how the World is Viewed, Sight Impacts how the world is Felt
New research, published in the April 9,2009 online issue of Current Biology, reinforces the suspicion that senses play off of and reinfoce one another, to an even greater extent. In this case, MIT neuroscientists have found a corollary to the visual illusion process in the tactile sensory systems of humans.
Motion after effect, when it occurs in visual perception, tricks us into believing that things are moving when they are not. The example given in the paper is that, if you stare at a large waterfall for a period of time, such that the waterfall is all you see, it will start to appear as if the rocks embedded in it are actually moving upwards rather than the water moving down.
The discovery with tactiles is very much the same. If you feel something and it appears to be moving, something which your skin brushes up against that isn't moving, will feel to your senses that it is moving in the opposite direction. If you then look at the object you are touching, without an external frame of reference, your eyes will actually reinforce the impression that the second surface is in fact moving, building on the initial impression from the sense of touch.
In this way, unless there is competing information that the second sense supplies, senses build upon the initial assumptions of one another. For virtual environments, this finding is key: Once one sense is fooled, bringing another into the equation, under the control of the VR interface, the illusion is only reinforced, not dispelled.
In the experiments, 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 centimetre-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.