In early September 2013 I visited a laboratory at the University of Pittsburgh Medical Center, and by pre-arrangement met a research subject, an ex-policeman who had become blind a few years previously. He sat at a table, put on some dark glasses with a small protruding lens, placed a small flat plastic device in his mouth, and proceeded to reach out and touch a series of small brightly coloured objects, including cubes and spheres. A twenty-first century Molyneux man. The videofeed from his glasses was being output on a nearby monitor, and I could see what his glasses were pointed at. The shapes on the monitor were being converted into an array of electrical patterns on the surface of his tongue, and although he could not see the objects with his eyes, he was feeling their shapes and responding appropriately. Soon, it was my turn. It didn't take long to put the equipment on, and after some acclimatisation I could start to discern objects in vague locations based on tingling patterns. If I looked to the left, the patterns would drift to the right side of the tongue; if I moved closer, the objects would increase in size on the tongue surface. With more time, I have been told, my brain would adapt, the accuracy would increase, and tasks such as reading letters and numbers, or playing games, would be possible. All through patterns of stimuli on a 20 × 20 array of electrodes on the tongue. This technology, which can make blind subjects ‘see’, is called the BrainPort™ V100 sensory substitution device.

Previously, the notion of ‘seeing with the hands’ was an analogy, a means by which Descartes could explain the mechanisms of sight. Likewise, the analogy of ‘reading with the fingers’ was applied to decoding tactile signs or mechanically augmented learning materials, such as Braille or tactile maps, through the fingertips. While the language of equivalence in those cases is largely a rhetorical flourish, this chapter's examination of technologies of sensory substitution will subject the suitability of such analogies to more scrutiny. Over the past few years there has been coverage in mainstream media, and discussion in the philosophy and psychology literature, of technologies that allow blind subjects to ‘see’ through the skin and the tongue.