The following text is an abbreviated translation from my master thesis, which can be downloaded here.
Hallucinations have been the subject of popular and scientific interest.
The first person to approach flicker light induced hallucinations scientifically was the Czech physiologist Jan Purkinje. He would wave his fingers in front of his closed eyes while looking into the sun. In his thesis “Beiträge zur Kenntnis des Sehens in subjectiver Hinsicht” 1819 he describes the synthesising activity of the senses and presents a set of detailed drawings of his visual impressions. About one hundred years later, 1928, Heinrich Klüver will call those patterns form-constants. While researching Mescalin induced visions, he found that there are four classes of patterns: (1) lattices (including gratings, fretworks, honeycombs, filigrees, and chessboard designs), (2) cobwebs, (3) tunnels (including alleys, funnels, cones and vessels), and (4) spirals.
In the year 1838 the psychophysiologist G.T. Fechner investigated the capacities of the visual senses. In order to create different shades of grey, he constructed a rotating disk with a set of black segments. Fechner was quite surprised to see brilliant colours that changed their hue depending on the speed and direction of the rotation.
Charles Edwin Benham brought the subjective visual illusion of the Fechner – colours to a wider audience. Benhams Artificial Spectrum Top was part of the 1894 Edition of Nature magazine and became one of the most valuable tools in studying the visual perception.
Turned clockwise the outer ring becomes violett, the next greenish then a pale blue while the innermost ring becomes red. A change of direction reverses the order of the colours.
Fechner tried to explain those subjective colours on the assumption of different speeds for the perception of colours in the retina. But this would not explain a change of colour as soon as the disk turns in the opposite direction. Campenhausen und Schramme (1995) come to a different conclusion:
[…] the phenomenon originates in phase-sensitive lateral interactions of modulated neural activity in the retina followed by additional spatial interactions in the visual cortex behind the locus of binocular fusion. (Campenhausen und Schramme 1995)
Flicker proved to be a key to many doors.
W. Grey Walter
W. Grey Walter
W.G. Walter is a key figure in neurophysiological research. He further developed the electroencephalograph invented by Hans Berger. In 1936 he recorded the EEG of a brain tumor patient when he discovered the characteristic frequency of 1 Hz. This work led to a new era in the diagnostics of brain lesions. In 1943 he found the Theta-Rhythm and used flicker light to diagnose epilepsy.
In order to study the EEG patterns of epileptics he compared several hundred kids, students and adults. In 3 to 4 percent of test persons seizure like patterns could be evoked by carefully tuning the flicker frequency. Walter devised an electronic circuit to control the stroboscope directly from the EEG. With such a feedback loop more than 50% of his test persons experienced seizure like episodes.
While working with high powered stroboscopes Walter noticed lively illusions and moving patterns, significantly between 8 and 25 Hz. His test subjects reportedly saw pulsating chessboard patterns, mosaics, rotating spirals and firework explosions. They also reported non-visual perceptions, such as an “out-of-balance” feeling, the feeling of jumping or turning, a tickling on the skin.
Walter asks how it can be, that the precise repetition of a flash of light evokes a colourful moving pattern
The imaginary patterns provided by flicker in conjunction with alpha rhythms are produced in the brain. Their movement is the movement of some hitherto unsuspected mechanism of the brain. What is this mechanism? (Walter 1953)
Walter – with his background in the electrical engineering of radar technology – believes that the brain performs a scanning mechanism. The alpha-rhythm of around 10Hz being the sampling frequency. He suggest two other facts to prove his theory:
- One can read approx. 100 words in 10 sec. That is 10 Words per second, or 10 Hz
- Max Wertheimers (1912) beta phenomenon experiment demonstrates the apparent movement of images that are actually static. This illusion of motion occurs, as soon as the images are presented at a rate of 10 Hz.
W. Grey Walters Book “The living brain” had a big influence on some of the key figures of the Beat-Generation. Fascinated by the idea of Bio-Feedback, W.S.Burroughs suggested to do several self-experiments. Reportedly, Allen Ginsberg – on taking his first dose of LSD in the Palo Alto Mental Research Institute – suggested to hook up his EEG with a stroboscope:
“It was like watching my own inner organism,” said Ginsberg. “There was no distinction between inner and outer. Suddenly I got this uncanny sense that I was really no different than all of this mechanical machinery around me. I began thinking that if I let this go on, something awful would happen. I would be absorbed into the electrical network grid of the entire nation. Then I began feeling a slight crackling along the hemispheres of my skull. I felt my soul being sucked out through the light into the wall socket and going out.” (Lee und Shlain 1992, S. 53)
“The living brain” offered an explanation to a unique experience that Brion Gysin on a bus ride thru an alley:
‘an overwhelming flood of intensely bright patterns in super- natural colours exploded behind my eyelids: a multi-dimensional kaleidoscope whirling out through space. The vision stopped abruptly when we left the trees. Was that a vision?’. (Meulen u.a. 2009)
The trees of the alley dissected the continuous light of the sun into separate flashes. Together with the math student Ian Sommerville, Gysin developed a device that could emulate this effect with simple and inexpensive means. The resulting “Dream Machine” consisted of a record player set on 78 rpm, a 100 Watt light bulb and a paper cylinder into which holes where cut. Sitting with closed eyes in front of this setup would trigger colourful hallucinations in the observer.
Gysin believed that their “Dream Machine” would drive-out the TV-sets from living rooms. He even filed a patent “for ‘a procedure and apparatus for the production of artistic sensations’ “ (Meulen u.a. 2009) and got into contact with the technology company Philips. But in the end, the “Dream Machine” was not mass-produced.
In the years 1965/66 Ken Kesey and his Band of Merry Pranksters took LSD and the stroboscope out of the lab and into the streets. Tom Wolfe describes what happened in this parties in “The electric Kool-Aid Acid Test”:
The strobe! […] The strobe has certain magical properties in the world of the acid heads. At certain speeds stroboscopic lights are so synched in with the pattern of brain waves that they can throw epileptics into a seizure. Heads discovered that strobes could project them into many of the sensations of an LSD experience without taking LSD. The strobe! To people standing under the mighty strobe everything seemed to fragment. Ecstatic dancers—their hands flew off their arms, frozen in the air—their glistening faces came apart—a gleaming ellipse of teeth here, a pair of buffered highlit cheek- bones there—all flacking and fragmenting into images as in an old flicker movie—a man in slices!—all of history pinned up on a butterfly board; the experience, of course. The strobe, the projectors, the mikes, the tapes, the amplifiers, the variable lag Ampex—it was all set up in a coiling gleaming clump in the Lincoln Log lodge, the communal clump, Babbs working over the dials, talking into the microphones to test them. Heads beginning to pour in. Marshall Efron and Norman, Norman already fairly zonked … Then in comes Kesey, through the main door (Wolfe 1999)
Here the strobe is not used to gain insight into ones own perception, or to reach a transcended state of mind thru alpha-wave conditioning. It is used to amplify an LSD-trip. In that sense Keseys Acid Tests might signify the transition from the Beat- to the Hippie-Movement.
Humphrey Osmond and John Smythies investigated the psychotomimetic experiences evoked by Mescalin. In contrast to psychoactive substances the stroboscope offered a way to analyse the function of the brain in extreme situations. “The stroboscopic patterns” (1959) is an extensive study of flicker light induced visual phenomena. Smythies hoped to deduce principles of visual pattern recognition by analysing the forms and transformations of the perceived patterns. He uses Grey Walters assumption of a scanning mechanism:
Suppose that we have a television mechanism employing scanning, and the problem is to find out the form of the raster employed without inspecting the screen closely. This may be done by asking the studio to be illuminated by an intermittent light at various frequencies. As soon as the flash of frequency falls below the frame frequency, ‘illusory’ geometrical patterns will appear on the screen[…] (Smythies, 1959)
The form of these patterns is determined by the scanning raster: a polar scan produces circles and circle segments, while a radial scan produces radial arrangements. In that way the details of the stroboscopic patterns tell us about our brains process of perception.
Ermentrout, Stoffregen and Rule (2011) proposed a computational model for the spontaneous formation of geometric patterns in the presence of flickering light. They define flicker induced phosphenes as visual hallucinations – often in the form ob basic geometric patterns – created thru temporal modulation of spatially unstructured light. The theory suggests, that they emerge thru a combination of resonance and lateral inhibition. (see Ermentrout and Billock 2013).
In contrast to Stwertka (1993), who regards flicker phosphenes as dissipative structures, Ermentrout at.al use a variation of the Wilson-Cowan equation to simulate the effects of flicker in a spatial neural network. The Wilson-Cowan model does not care about the behaviour of single neurons, but describes the dynamic interaction between the population of neurons. The fundamental assumption of the Wilson-Cowan model is, that all nervous processes, independent of their complexity, depend on the interaction between excitatory and inhibitory neurons.
Between the retinal coordinates and the cortical coordinates there exists a topographical mapping that is: a point (r, θ) in polar coordinates on the retina is mapped to (log r, θ)
in Cartesian coordinates in the cortex. Therefore, a retinal image of concentric circles is mapped to vertical lines in the cortex. See fig. C below.
- The results of the computational simulation are consistent with the reports of flicker light stimulated humans.
The model also shows states of multi-stability. At a flicker frequency of 55 ms (18,18 Hz) vertical, horizontal and diagonal stripes are possible. These would translate to circles, spirals or pinwheels in retinal coordinates. - At fast stimulation rates (>12Hz) the spatial frequency of the pattern is twice that of the flicker frequency. The pattern is shifting for half of a spatial cycle each repetition, thus creating a standing wave in which the foreground and background are perfectly symmetric and alternate with each stimulus. This constant change would possibly be perceived as motion, expanding pulsating circles or rotating pinwheels.
- Between 8 and 12 Hz the model produces primarily hexagonal patterns. Unlike the stimulation with high flicker frequency these patterns have the same spatial period as the stimulus. Foreground and background are distinctive patterns, pulsating on and off alternately. See fig. E above.
Phosphene Activity is a stand-alone installation for one person at a time.
It consists of:
A flat surface to lay down. Six transducers are mounted on the underside of the surface. Thru precise tuning of the sound-sources it is possible to produce vibrations in a very low frequency range.
An audio-reactive stroboscope. Two 100Watt LEDs fire a load of photones into a papier mache hemisphere, placed over head and torso of the hallucinator.
Two speakers positioned on both sides of the head.
