Touch and sight push each other around
When the fingers feel downward motion, the eyes see upward motion
What people see sometimes depends on what they just felt, a study appearing online April 9 in Current Biology shows. A light ripple of pins moving up the fingertip tricked study participants into perceiving lines on a screen as moving down, and vice versa, suggesting that vision and touch are integrated in the human brain.
“I think this is an important advancement,” comments Jon Kaas, a neuroscientist at Vanderbilt University in Nashville. “It changes our way of thinking about how the brain works.”
For decades, instructors in medical schools have taught students that the senses —including vision, touch and sound — are interpreted in different, discrete parts of the brain, says Michael Beauchamp of the University of Texas Medical School at Houston. “Now it turns out what we’re teaching them is wrong,” he says. “There’s a lot more cross talk between the modalities.”
Recent studies have shown a close link between hearing and vision. To understand the presumed links between touch and vision, researchers led by Talia Konkle and Christopher Moore of the Massachusetts Institute of Technology in Cambridge employed a trick of perception called an aftereffect.
Watching a waterfall causes one well-known motion aftereffect. After a person stares at the falling water long enough, the stationary rocks at the bottom appear to float upward. One predominant explanation, Moore says, involves brain fatigue. Some nerve cells in the brain detect things moving down, while others detect things moving up. The “down” neurons get tired when a person stares at water plunging downward, but the “up” neurons are still fresh and active, causing the rocks to appear to float.