It is Paris, 1883. Impressionism is at its height, and Monet is painting light and lilies at Argenteuil. A few kilometres along the Seine, at Paris's world-famous Salpetriere Hospital, Professor Jean Charcot- a pioneer of hypnosis and major influence on Freud- opens a letter from a patient, Monsieur X. This successful, intelligent man- fluent in French, German, Spanish, Latin and ancient Greek- describes how something terrible has happened to his mind. He is now suddenly blind in his mind's eye.

Up until then, M. X could visualize with the vividness of actual seeing. He only had to read something two or three times before is was etched on his mind and he could read it off as if it were chalked on a blackboard. From memory he could make sketches of places he had been as if drawing them in front of his eyes.

But what had happened? A period of business stress and suddenly, without warning, a bulb blows in his mental screen. He complains that his previously vivid imagination has gone: ' I used to be impressionable, enthusiastic, and I had a vivid imagination: today I am calm, cold and my imagination cannot lead me astray.' He mourned the loss of vivid dreams:'Now I only dream in words.'

The gift may have been in his genes- his professor brother, orientalist father and painter sister all have it. Now he can't imagine the faces of his wife and children, he can't let his imagination playfully toam through the wordless realsm of image: 'If you were to ask me to imagine the towers of the NOtre Dame, a grazing sheep or a ship in distress in the open sea, I would answer that , although I know perfectly well how to distinguish these three very different things and know very well what they are about, they have no meaning for me in terms of internal vision.'

M. X was much less affected by grief now. For instance, after one of his relatives died, he could not mentally picture the man's features, his suffering, or the grief of his family. He blames this blunted sorrow on the loss of his mind's eye. Generally, he feels crippled by the loss of his mind's eye: ' I now have to say to myself the things I want to remember, whereas in the past I would only have to photograph them by sight.'

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Not only can words project pictures on the mind's eye, then- they can also fill the mind's ear with sounds. Some poets cater more for the mind's ear, others for the eye. Others write in highly abstract language that does not easily generate visual or other images. Poetry changes the brain in different ways, but most poets trade heavily on the currency of imagery.