From: Cathy Reason <Cathym.nul> Date: Sun, 22 Apr 2012 19:04:46 +0100 Archived: Mon, 23 Apr 2012 07:08:58 -0400 Subject: Re: Ufology And Psychiatry - Summary >From: Eugene Frison <cthulhu_calls.nul> >To: <post.nul> >Date: Sat, 21 Apr 2012 19:06:42 -0500 >Subject: Re: Ufology And Psychiatry - Summary <snip> >What vision researchers? What are these mechanisms by which the >brain extracts information from the visual world? What >experimental artifacts? What hypotheses are being tested on how >the visual system behaves in highly novel and constrained ways? >Can you tell us what these novel and constrained ways are? What >have these tests reveiled about how the visual system behaves in >novel and constrained ways? Don't just claim something _is_. >Give us something we can sink our teeth into. The phrase about pots and kettles comes to mind, but ok. Let's try the example of the Kanizsa Triangle. This is an illusion in which only the corners of the triangle are actually defined - the sides of the triangle just aren't there. Nonetheless when we look at the illusion we see a complete triangle. The sides are added in by a process known as illusory contouring. This is actually very useful. For example, out of my window now I can see a row of houses with a tree standing in front of them. I can't actually see all the houses, because the tree obscures the view. Nonetheless when I look at the houses, I see a row of ordinary houses, and not a row of houses with a peculiar tree- shaped hole in one of them which just happens to be hidden behind an actual tree. Although the some of the contours of the houses are not directly visible, they are added in by the illusory contour mechanism. Two interesting points here: First, the mechanism which computes these illusory contours seems actually to be quite simple. There are a number of models for producing illusory contours, and although we don't know exactly how the brain does it, all the models rely on highly specific local processing algorithms. There is no need of any sophisticated top-down interpretation by some sort of "narrative-constructing" homunculus. Second point: Although we're happy to call these things illusory contours, I can't think of a single _natural_ example in which the contours are in fact illusory. In all real-life examples the contours really are there, it's just that they aren't _directly_ visible. This is why vision-researchers often don't call this an illusory contour mechanism at all, but a boundary completion operator. If you want to say that the brain _infers_ the boundaries, I guess that's ok, just so long as we realize that the inferencing mechanism is actually very simple and local, and doesn't require any sort of intelligent top-down processing of the sort beloved by cognitive psychologists. However - this illusion regularly appears in psychology textbooks as an example of how unreliable human perception is supposed to be because, it's said, we see things that just aren't there. Cathy Listen to 'Strange Days... Indeed' - The PodCast At: http://www.virtuallystrange.net/ufo/sdi/program/ These contents above are copyright of the author and UFO UpDates - Toronto. They may not be reproduced without the express permission of both parties and are intended for educational use only.
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