The cognitive science journal Cortex has just released a special issue on the neuropsychology of paranormal experiences and belief, and contains a fantastic article on hallucinations induced by the Ganzfeld procedure.

The Ganzfeld procedure exposes the participant to ‘unstructured’ sensations usually by placing half ping-pong balls over the eyes so they can only see diffuse white light and by playing white noise through headphones.

It is probably best known for its uses in parapsychology experiments, but it is also used to induce hallucinations and sensory distortions which are much more likely to occur in the absence of clearly defined sensory experiences.

The article reviews the sorts of hallucinations reported in during these experiments and discusses what electrophysiology (EEG or ‘brain wave’) studies tell us about what happens in the cortex when these perceptual distortions kick off.

Some of the descriptions of hallucinations are really quite striking:

“For quite a long…