Stare at a waterfall long enough, and nearby stationary objects such as rocks and trees will seem to drift up. The optical illusion is called motion aftereffect, and it may trick more than just your eyes, according to a new study. When subjects watched a stationary stripe on a computer screen after a machine stroked their fingertips, the motion of the stroking created the illusion that the stripe was moving. The discovery demonstrates for the first time a two-way crosstalk between touch and vision, challenging long-held notions of how the brain organizes the senses.
In 2000, neuroscientist Christopher Moore, now at the Massachusetts Institute of Technology in Cambridge, noticed that when a vibrating device buzzed a subject's fingertips, the visual motion detector in the brain fired up. But he immediately dismissed the result. At the time, researchers thought that the brain processes each sense–taste, touch, smell, sight, and hearing–separately and that it only later combines them to interpret the world. Over the past 5 years, however, further studies have challenged this picture. Experiments with blind subjects, for example, have found that reading Braille by touch can trigger activity in the brain's visual cortex (ScienceNOW, 8 November 2002). Researchers attributed the phenomenon to the brain rewiring itself to compensate for disability. But Moore and graduate student Talia Konkle wondered if the sight-touch link might lurk in everyone and if one sense might influence the other.
(Note: Picture shows DaVinci's paintbrush. By tapping a pattern on a fingertip, this array can create an optical illusion.)