A researcher from the University of Essex has succeeded in inducing the experience of colour in the blind part of a partially sighted patient’s visual field.

Using a magnetic coil to stimulate the patient’s brain, Juha Silvanto demonstrated for the first time that it is possible to experience visual sensations of colour in an area of blindness caused by a cortical brain lesion.

Dr Silvanto, a lecturer in visual perception from the Department of Psychology, explained: ‘We demonstrated that the undamaged side of the patient’s brain had taken over the function of colour perception.

‘This technique demonstrates that it is possible to restore visual awareness but we don’t yet understand the neural mechanisms. If further research enables us to uncover this process, it opens up the possibility of therapeutic treatment.’

Working with Alan Cowey from the University of Oxford and Vincent Walsh from University College London, Dr Silvanto tested a patient who had suffered damage to the primary visual cortex of his brain in a childhood accident. The lesion to this part of his brain considered essential for vision has left him with a reduced field of vision on his right side.

The researchers demonstrated that the colour shown to the patient’s intact (left) visual field determined what colour he saw in his blind field. By first presenting a red stimulus to his intact visual field, this created the sensation of seeing red also in the blind field when his visual cortex was subsequently stimulated using magnetic stimulation.

The partially sighted patient had previously been unable to experience visual perception in his blind field for more than 40 years.

While this was a short-term effect, it opens up the prospect of developing longer-lasting therapy to recover visual function, for example in stroke patients.

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Notes to Editors
The researchers’ findings "Inducing conscious perception of colour in blindsight" were published this week in Current Biology.