293. Study of Vision Tackles a Philosophy Riddle

William Molyneux

By Nicholas Bakalar, The New York Times, April 25, 2011

If a blind person were suddenly able to see, would he be able to recognize by sight the shape of an object he previously knew only by touch? Presented with a cube and a globe, could he tell which was which just by looking?

The question goes to the heart of a problem in the philosophy of mind: Is there an innate conception of space common to both sight and touch, or do we learn that relationship only through experience? Research published online April 10 in the journal Nature Neuroscience may have finally answered the question, which has vexed philosophers and scientists for more than 300 years.

William Molyneux, an Irish politician and scientist, first raised the issue in a letter to John Locke in 1688. Locke took up what came to be known as Molyneux’s problem in “An Essay Concerning Human Understanding,” published a few years later.

Locke’s answer was no. “He would not be able with certainty to say which was the globe, which the cube, whilst he only saw them,” he wrote, “though he could unerringly name them by his touch.” For Locke, the connection between the senses was learned.

Dozens of philosophers have since considered the problem, among them George Berkeley, Gottfried Leibniz, Voltaire, Diderot, Adam Smith and William James. And some efforts have been made to answer the question experimentally, beginning in the early 18th century with studies of patients whose congenital cataracts had been removed in adulthood and continuing recently in observations of newborns.

But according to the authors of the new experiment, the studies have been inadequate, never establishing how well the patient could see afterward, or failing to test soon enough after surgery so that the subject was still completely inexperienced with vision.

The new research appears to show definitively that Locke was right. The brain cannot immediately make sense of what the eyes are taking in, and the blind man given the ability to see cannot distinguish the two objects. But he can very quickly learn to do so.

Working with a group that provides medical treatment to the blind and visually impaired in resource-poor countries, the researchers tested five subjects from rural northern India, four boys and a girl ages 8 to 17. A all had been blind since birth, one with a disorder of the cornea, and the others with cataracts. Before their operations they could perceive light, and two could discern its direction, but none could see objects. Afterward, they all had vision measured at 20/160 or better, good enough to distinguish objects and carry out the tasks of daily living.

The children were tested within 48 hours of their operations. The researchers placed 20 small objects similar to Lego blocks on a table where they could be seen, but not touched. Then they had the children feel identical blocks under the table where they were invisible, and try to match them with those they could see. The average performance in matching one object with another by either touch or sight alone was high, close to 100 percent. Yet when they were asked to match an object they had felt with an object seen, the average number of correct answers dropped to barely better than chance.

But improvement was rapid. A co-author of the study, Yuri Ostrovsky, a postdoctoral fellow at M.I.T., said one child was proficient in less than a week. Within three months, the average number of right answers in matching an object seen with one touched was above 80 percent.

The lead author, Pawan Sinha, a professor of vision and computational neuroscience at M.I.T., believes that answering the philosophical question is not the only benefit.

“This paper strengthens the case that cross-modal learning is possible despite years of deprivation,” Dr. Sinha said. “That’s very important from a clinical perspective because it argues for making a treatment available to all, irrespective of age. Children beyond 6 or 7 are not beyond the correctable age. The brain retains its plasticity well into late childhood and even into adulthood.”