Tuesday, March 01, 2005

Endogenous Video Feedback

Entoptic is a general term used to describe endogenous imagery, such as phosphenes or the closed eye visuals produced by many psychedelics. Entoptic images can be shaped as spirals, latices, cobwebs, tunnels, etc, as in the following illustration (from the classification of phosphenes by Max Knoll, 1965):

In the 70s, anthropologist Gerardo Reichel-Dolmatoff noticed entoptic patterns in the art of the Tukano (in Colombia). He extensively documented the images seen in the early stages of the yage (ayahuasca) experience.

In their 1988 article "The Signs of All Times" (Current Anthropology 29:201-245), Lewis-Williams and Dowson postulated entoptic phenomena (experienced by shamans in trance states, possibily induced by psychoactive agents) form the basis for images in Upper Paleolithic cave art.

I have talked about video feedback before (the feedback loop that happens when a video camera is pointed to the monitor). Now, compare entoptic patterns with images produced by video feedback. I think the similarity is remarkable. My idea is that a process equivalent to video feedback might take place in the visual cortex. A biological counterpart of an optoelectronic feedback loop. The image of the homunculus playing with a video camera comes to my mind ;) but what I'm actually suggesting is that perhaps we project back to the striate cortex what we're aware of. If such process occurs within the visual cortex, backprojections from higher cortical areas to V1 must be involved in the generation of entoptic imagery. Supporting this idea, there is evidence that the backprojection from V5 to the V1 is necessary for the perception of moving phosphenes (evoked by magnetic stimulation of V5).

Furthermore, Lewis-Williams and Dowson formulate seven principles of perception for entoptic images: Replication, Fragmentation/Integration, Superpositioning/Juxtapositioning, Reduplication, and Rotation. Those principles are the sort of image transformations that apply in each iteration of a video feedback loop.

Here are some links and references:
Form & Meaning in Altered States & Rock Art
Altered States: The Origin of Art in Entoptic Phenomena
Dr. Tom's Video Feedback Gallery
The Ultimate Video Feedback Page
Daniel A. Pollen, 'On the Neural Correlates of Visual Perception'
Silvanto et al, 'Striate cortex (V1) activity gates awareness of motion'
Juan, Walsh, 'Feedback to V1: a reverse hierarchy in vision'


Blogger an orange said...

Wow, what an interesting connection you made. Your observations are great - I'm bookmarking your blog.

3/03/2005 9:11 AM  
Blogger Tim Brown said...

Cool idea... the similarities are striking.

Paul Bresselof at the U. of Utah in the US has done some pretty cool math models of how our visual cortex might generate hallucinations. I saw him give a talk about his work before they hired him -- good stuff.

A couple of papers:
P. C. Bressloff, J. D. Cowan, M. Golubitsky, P. J. Thomas and M. Wiener, What geometric visual hallucinations tell us about the visual cortex Neural Comput. 14 : 473-491 (2002).

P. C. Bressloff and J. D. Cowan, Spontaneous pattern formation in primary visual cortex In: Nonlinear dynamics: where do we go from here? S. J. Hogan, A. Champneys and B. Krauskopf editors, chapter 11 (Institute of Physics: Bristol, 2002).

P. C. Bressloff, J. D. Cowan, M. Golubitsky, P. J. Thomas and M. Wiener, Geometric visual hallucinations, Euclidean symmetry and the functional architecture of striate cortex Phil. Trans. Roy. Soc. B 40 :299-330 (2001).

PDF's are at:

7/22/2005 9:13 AM  
Anonymous Anonymous said...

I believe that some hallucinogens reduce the synaptic resistance, allowing action potentials that would otherwise extinguish to propagate.

If this is true, the effect of these hallucinogens is to allow us to perceive natural nervous system and brain events that would otherwise be below the threshold of perception or even much lower layers of processing.

It has been demonstrated that the visual cortex, possibly in conjunction with retinal processing detects patterns - lines for example, the shape of a face, or moving objects.

Therefore random action potentials in these structures, when allowed to propagate due to reduced synaptic resistance would produce perceptions specific to the pattern processing structures.

7/25/2005 1:32 PM  

i do not know if you speak spanish
as i see you live in argentina

very good subject
morris berman talks about williams in his book
who says among other things
that what some call god williams calls the nervous sistem
i think the inconciuos seak of these patterns
makes the world believe in a kind of god realted to this

good blog
if you read spanish
your invited to mine

1/08/2008 11:24 AM  
Blogger Josue said...

great findings. I am someone that has studied both communications with an emphasis in communications technology and psychology. I know that through audio you can send subliminal messages through music or any kind of sudio recording. It can be broadcasted directly through the music or at such a low frequency that the normal radio or television will not be able to pick it up and can directly effect someones subconscious. I was wondering will it be possible to take a video loop of anything or even live video, broadcast it at the same low frequency having the same effect. During one of my experiments I had volunteers try a variety of substances at a low dose, they were all seperated and I recorded their experiences indivudually so they wouldnt be able to hear each others response and contaminate the experiment. For this one substance in particular they all had the same hallucination and the same experience as if they were watching a video loop on the tv. I found it very interesting that they all had the same experience. To recreate my experiment I got a new volunteer and with them having no knowledge of the other volunteers I gave them the same substance and found that they had the same experience. I would like to have your views and throughts on this subject. Please contact me at: jesusemp@yahoo.com (All of the volunteers are fine and are not addicted to the substance)

7/04/2011 5:07 PM  

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