Molyneux's problem

Original correspondence

The question was originally posed to Locke by philosopher William Molyneux, whose wife was blind:

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 is the sphere. Suppose then the cube and the sphere placed on a table, and the blind man made to see: query, 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, and how a cube, affects his touch; yet he has not yet attained the experience, that what affects his touch so or so, must affect his sight so or so…'

To which Locke responds in An Essay Concerning Human Understanding:

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.

Responses

In 1709, in A New Theory of Vision, George Berkeley also concluded that there was no necessary connection between a tactile world and a sight world—that a connection between them could be established only on the basis of experience. He speculated:

the objects to which he had hitherto used to apply the terms up and down, high and low, were such as only affected or were in some way perceived by touch; but the proper objects of vision make a new set of ideas, perfectly distinct and different from the former, and which can in no sort make themselves perceived by touch

In 1749, Denis Diderot wrote Letter on the blind for the benefit of those who see as a criticism of our knowledge of ultimate reality.

Scientist and politician William Molyneux proposed a problem in a correspondence with Locke that involves the differences between modes of perceptions and true understanding.

Locke himself believed that sight and touch were entirely different sense perceptions and thus the blind man could not distinguish the sphere from the cube at first sight.

A similar problem was also addressed earlier in the 12th century by Ibn Tufail (Abubacer), in his philosophical novel, Hayy ibn Yaqdhan (Philosophus Autodidactus). His version of the problem, however, dealt mainly with colors rather than shapes.

Regarding Molyneux's problem, the authors Asif A. Ghazanfar & Hjalmar K. Turesson (2008) have recently noted:

Production of speech is seen as a pure motor act, involving muscles and the neurons controlling them, while perception of speech is seen as purely sensory, involving the ear and the auditory pathway. This parcellation of the systems appear intuitive and clear, but recent studies [beginning with Taine 1870!] … suggest that such divisions may be fundamentally wrong. Rather than separate processes for motor outputs and individual sensory modalities, adaptive action seems to use all the available context-specific information. That is, neural representations across the brain may be centered on specific actions. This view on neural representations puts 'Molyneux's Problem' in a new light. Unisensory signals are fused into multisensory motor representations unified by an action, but since Molyneux does not suggest any action, his 'problem' may be better viewed as an ill-posed question—at least from a neuroscientific perspective.

One reason that Molyneux's Problem could be posed in the first place is the extreme dearth of human subjects who gain vision after extended congenital blindness. Alberto Valvo estimated that fewer than twenty cases have been known in the last 1000 years. Ostrovsky, et al., studied a woman who gained sight at the age of 12 when she underwent surgery for dense bilateral congenital cataracts. They report that the subject could recognize family members by sight six months after surgery, but took up to a year to recognize most household objects purely by sight.

In 2003, Pawan Sinha, a professor at the Massachusetts Institute of Technology, set up a program in the framework of the Project Prakash and eventually had the opportunity to find five individuals who satisfied the requirements for an experiment aimed at answering Molyneux's question experimentally. Prior to treatment, the subjects (aged 8 to 17) were only able to discriminate between light and dark, with two of them also being able to determine the direction of a bright light. The surgical treatments took place between 2007 and 2010, and quickly brought the relevant subject from total congenital blindness to fully seeing. A carefully designed test was submitted to each subject within the next 48 hours. Based on its result, the experimenters concluded that the answer, in short, to Molyneux's problem is "no". Although after restoration of sight, the subjects could distinguish between objects visually almost as effectively as they would do by touch alone, they were unable to form the connection between an object perceived using the two different senses. The correlation was barely better than if the subjects had guessed. They had no innate ability to transfer their tactile shape knowledge to the visual domain. However, the experimenters could test three of the five subjects on later dates (5 days, 7 days, and 5 months after, respectively) and found that the performance in the touch-to-vision case improved significantly, reaching 80–90%.