As part of this study, we constructed a mathematical model of the visual cortex that reproduces much of the perceptual behaviour of the hallucinations. The neural activity in our model self-organises into patterns of spirals and stripes that bear an uncanny resemblance to the hallucinatory patterns. The patterns only emerge for flicker frequencies near 11 Hz. If the flicker is too slow, or too fast, then the model reproduces the physical stimulus, as is the case in human perception. Interestingly, the same patterns spontaneously alternate with their negative image. These alternations occur at half the frequency of the flicker stimulation. They evoke a sense of apparent motion that resembles the motion of the illusory blobs reported by humans. The illusory motion is most evident when the flicker is constrained to an annulus, as was the case for the psychophysical experiments.
Selected Media reports
- Did you see that? Inducing visual hallucinations in healthy people. Neuroscience News, 12 Oct 2016.
- Measurable hallucinations induced for the first time. IFL Science, 12 Oct 2016.
- Scientists can make people hallucinate using flickering image. Live Science, 15 Oct 2016
- Scientists found a way to induce visual hallucinations in healthy people without the use of drugs. Science World Report, 18 Oct 2016.
- Pearson J, Chiou R, Rogers S, Wicken M, Heitmann S, Ermentrout GB (2016) Sensory dynamics of visual hallucinations in the normal population. eLife Vol 5. e17072.
- Billock & Tsou (2012) Elementary visual hallucinations and their relationships to neural pattern forming mechanisms, Psychol Bull. 138:4. p744.
- Ermentrout & Cowan (1979) A mathematical theory of visual hallucination patterns. Biological Cybernetics. 34:137-150.