Measurable Hallucinations Induced For The First Time


Stephen Luntz

Stephen has a science degree with a major in physics, an arts degree with majors in English Literature and History and Philosophy of Science and a Graduate Diploma in Science Communication.

Freelance Writer

ring with blobs

The blobs seen here are similar to what is hallucinated when a white ring is flashed 5 to 30 times a second. For the first time, a hallucination like this can be measured. Pearson et al/eLife

Warning: The study's authors recommend that anyone with a history of migraines, epilepsy or psychiatric disorders refrain from watching the video below

Hallucinations are, by their nature, hard to study. People struggle to describe what they see, and efforts to have the hallucinator draw their visions seldom adds much precision. So Dr Joel Pearson of the University of New South Wales is excited about the potential of the first method to produce hallucinations that can be objectively measured. 


Hallucinations caused by psychosis or drugs are usually too complex to measure on a single scale. For more than a century we have known that flickering lights, along with certain combinations of light and dark, can induce visual hallucinations, and these are simpler.

However, Pearson told IFLScience, they are still not simple enough. “It's like trying to study the imagination,” Pearson said. To change this, Pearson set out to reduce what is seen to be a single, quantifiable feature. He announced his success in eLife.

Pearson's hallucinogen works by flashing a white ring up to 30 times a second on a black background. A group of student volunteers without a history of migraines or epilepsy reported seeing gray blobs rotating inside the ring, and Pearson showed he could control the brightness of these blobs through the rate at which the ring flashed. When a second ring with permanent blobs was added, participants compared the brightness of the real and hallucinated blobs.

If the flickering doesn't give you a headache, you should be able to see the moving blobs. Joel Pearson


As a first demonstration of the power of his technique, Pearson confirmed these hallucinations are subject to similar rules as for visual perceptions, such as stabilization memory and adaptation. “If you look at a waterfall long enough and then look at rocks, the rocks will seem to move up,” he told IFLScience. “No one had been able to test before that the same rules apply to hallucinations.”

Pearson showed volunteers two videos, one for each eye. Each light flickered 2.5 times a second, too slow to induce hallucinations, but by having the pair out of sync Pearson produced images equivalent to a ring flashing at five times per second.

“They were combining the signals from the two eyes. This really only happens in the visual cortex, not in the eye, or other initial processing areas of the brain,” Pearson said in a statement. The finding conflicts with one popular theory of hallucination, which suggests they result from parts of the brain responsible for attention misfiring, and supports those that locate the cause in the brain's visual processing center.

Pearson and his colleagues have received funding to use their technique to study the hallucinations experienced by sufferers of Parkinson's Disease. He acknowledged to IFLScience that “we don't yet now if these [flicker induced hallucinations] are related to those caused by LSD or disease.”


Nevertheless, some commonalities have been observed, and Pearson hopes his work will provide explanations for all sorts of hallucinations, and possibly methods to control them.

  • tag
  • hallucination,

  • visual processing,

  • measurable perception