Modeling visual hallucinations

psion005-abstract.jpgHeinrich Klüver (1897-1979) was an experimental psychologist at University of Chicago who did groundbreaking work in the emerging field of visual hallucination from the late 1920s through the 1970s. He conducted a range of self-experiments using peyote in a lab setting, recording as much subjective and objective data as he could while high.

Hallu.gifHe then categorized geometric hallucinatory images into four form constants: (I) tunnels and funnels, (II) spirals, (III) lattices, including honeycombs and triangles, and (IV) cobwebs.

Image by Psion005 @ deviantart. Used with permission.

He noted that this work might be useful for anthropologists and art historians looking at primitive art and cave paintings, where these patterns have sometimes been depicted. Subsequent neurologists have identified the hexagonal shape of structures in the primary visual cortex as a likely source for these patterns, when combined with "stripes" of neural activity (inhibition and excitation) that can occur under certain conditions, including sensory deprivation, pressing hard on both eyes, and when taking hallucinogens. These effects were even observed in some blind people.


This is related to the mathematics of periodicity I mentioned in the article on Hans Jenny and cymatics.

Jack Cowan, also of University of Chicago, has continued this interesting work and has helped develop mathematical formulas that model how these structures in the cortex generate these images. Basically, the visual cortex sends out waves in periodic bursts that ebb and flow, resulting in the amazing geometric patterns many people experience.

hallucination-pattern2.jpg For details, here's Dr. Cowan lecturing on the topic:

Geometric Visual Hallucination (Jack Cowan)



  1. A few years ago I found an article by Susan Carr on entoptic phenomena that categorized phosphenes.
    It’s at It doesn’t look like Carr had cited Dr. Cowan’s work, however.

    After looking at loads of similar motifs from different times and cultures across the world, I’d had a hunch that the motifs were caused by something from our physiology or a by-product of it at least.

  2. I did a little work on exactly this in 1982, when I was hobnobbing at AI conferences and thinking a lot about the rotation and scaling problem that was confounding real-world use of the spatial FFT. Someone had just laboriously discovered the logarithmic polar mapping between retina and primary visual cortex, and I modeled it (very crudely) on my Cromemco Z2D. The results were quite exciting, and for a time I was trying to fashion a “preprocessor” for visual pattern recognition along these lines, even imagining a screw-on fiber-optic adapter to do it in parallel… given the slow computers of the day.

    Here’s a short summary with a couple of pictures demonstrating the mapping:


  3. Please, please get your psychology right. Your articles on the DSM-V and evolutionary psych weren’t good, and confusing hallucinations with illusions is downright terrible. For future reference: A hallucination means that no stimulus is given. Confusing the senses with ambiguous stimuli is called an illusion.

    1. @Yenzo#3: The title of Dr. Cowan’s speech would indicate that hallucination is the correct term here, not illusion. Did you watch it before attempting to correct me?

      1. I did not watch the speech and I apologize if my criticism was not justified. With the pictures you used and the mentioning of Klüver, etc. I was quite sure that you were talking about illusions, so your post was at least a bit ambiguous in that regard.

        My criticism of your other articles still stands, however, and I’m sorry that I won’t have the time to discuss it in detail. Suffice to say there are some researching psychologists out there in whose opinion you are oversimplifying to the point of misrepresentation.

  4. He conducted a range of self-experiments using peyote in a lab setting, recording as much subjective and objective data as he could while high.

    Man, why do I never see adverts for such cool jobs? Here I am stuck in front of a computer…

  5. I’ve always wondered why pressing on one’s eyes caused such hallucinations, after discovering the effect as a kid (and promptly being warned not to do that to my eyes).

  6. I personally have these types of hallucinations from time to time. They are in the spiral category and seem to rotate CCW as the spiral extends away from me. It strobes and changes colors rapidly like the new light bars on a police car and interferes with my vision, as I cannot focus on anything. I tend to rely on my peripheral vision to navigate and take an nap. Once a little bit rested, it goes away.

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