From: Anders Sandberg (asa@nada.kth.se)
Date: Thu Jan 03 2002 - 08:32:06 MST
There has been some interesting modelling of hallucinatory patterns by
Bard Ermentrout at University of Pittsburgh
(http://www.pitt.edu/~phase/) and Paul Bressloff at Loughborough
University (http://www.lboro.ac.uk/departments/ma/staff/pcb/).
The idea is that drugs produce disinhibition in the visual cortex, which
leads to pattern formation. The fun thing is that you can model this
essentially as an ordinary reaction-diffusion system (there is a local
nonlinear interaction between excitation and inhibition, and they
diffuse with slightly different diffusion constants) which produces
spots, lines, hexagons and all the other usual patterns you see in
nonlinear science textbooks across the virtual cortex.
But since there is a nonlinear map between our visual field and the
cortex, a straight line of cortical activity would not appear to us as a
straight line, but a spiral. Paul showed that the most likely patterns
also correspond well to many common hallucinations, and when they moved
many common animated hallucinations appear. More complex interactions
between direction sensitive cells produce spiderweb patterns and so on.
Very elegant models.
It seems likely that since we all share the same basic visual hardware,
its modes of instability and resonance would affect us across culture,
especially during early childhood when the developing visual system
seems extra unstable. Many such phenomena are likely useful - the
spontaneous waves across the retina during fetal development are
believed to train the visual cortex for example.
-- ----------------------------------------------------------------------- Anders Sandberg Towards Ascension! asa@nada.kth.se http://www.nada.kth.se/~asa/ GCS/M/S/O d++ -p+ c++++ !l u+ e++ m++ s+/+ n--- h+/* f+ g+ w++ t+ r+ !y
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