Tuesday, May 03, 2011

Molyneux's Problem: Can the Blind Know How Shapes Look by Touch Alone?

In my modern philosophy class, we recently read this excerpt from John Locke's Essay Concerning Human Understanding, Book II, Ch. 9:

To which purpose I shall here insert a problem of that very ingenious and studious promoter of real knowledge, the learned and worthy Mr. Molyneux, which he was pleased to send me in a letter some months since; and it is this:- "Suppose a man born blind, and now adult, and taught by his touch to distinguish between a cube and a sphere of the same metal, and nighly of the same bigness, so as to tell, when he felt one and the other, which is the cube, which the sphere. Suppose then the cube and sphere placed on a table, and the blind man be made to see: quaere, whether by his sight, before he touched them, he could now distinguish and tell which is the globe, which the cube?" To which the acute and judicious proposer answers, "Not. For, though he has obtained the experience of how a globe, how a cube affects his touch, yet he has not yet obtained the experience, that what affects his touch so or so, must affect his sight so or so; or that a protuberant angle in the cube, that pressed his hand unequally, shall appear to his eye as it does in the cube."- I agree with this thinking gentleman, whom I am proud to call my friend, in his answer to this problem; and am of opinion that the blind man, at first sight, would not be able with certainty to say which was the globe, which the cube, whilst he only saw them; though he could unerringly name them by his touch, and certainly distinguish them by the difference of their figures felt.

But this has remained a philosophical riddle for over 300 years--until a couple of weeks ago, when a study was published in Nature: Neuroscience. This new study confirms the intuitions of Locke and Molyneux, who were in the minority at their time--other philosophers thought that a blind person would immediately be able to make use of restored sight.

The study worked with 5 subjects in resource-poor countries who had been born with severe cataracts or correctible corneal disorders but who had not been treated. The subjects were old enough (8 years or older) to have language skills and be able to interact with the researchers. Within just a couple days of corrective surgery, the subjects were not able to correlate the sight of Lego shapes with shapes they could feel but not see. However, within days to weeks, they were able to make the correlations--showing that experience is needed but that learning progresses rapidly. NYT article here.

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