From newshub.ccs.yorku.ca!ists!torn.onet.on.ca!utgpu!news-server.csri.toronto.edu!rutgers!att!linac!pacific.mps.ohio-state.edu!zaphod.mps.ohio-state.edu!mips!darwin.sura.net!europa.asd.contel.com!uunet!tdat!swf Tue Jun  9 10:07:27 EDT 1992
Article 6120 of comp.ai.philosophy:
Path: newshub.ccs.yorku.ca!ists!torn.onet.on.ca!utgpu!news-server.csri.toronto.edu!rutgers!att!linac!pacific.mps.ohio-state.edu!zaphod.mps.ohio-state.edu!mips!darwin.sura.net!europa.asd.contel.com!uunet!tdat!swf
>From: swf@teradata.com (Stanley Friesen)
Newsgroups: comp.ai.philosophy
Subject: Re: Grounding: Real vs. Virtual (formerly "on meaning")
Keywords: symbol, analog, Turing Test, robotics
Message-ID: <469@tdat.teradata.COM>
Date: 5 Jun 92 16:31:22 GMT
References: <600@trwacs.fp.trw.com> <1992May24.143025.7180@psych.toronto.edu> <zlsiida.347@fs1.mcc.ac.uk> <1992May27.161507.17921@guinness.idbsu.edu>
Sender: news@tdat.teradata.COM
Reply-To: swf@tdat.teradata.com (Stanley Friesen)
Organization: NCR Teradata Database Business Unit
Lines: 26

In article <1992May27.161507.17921@guinness.idbsu.edu> holmes@opal.idbsu.edu (Randall Holmes) writes:
| In the specific case of vision, two
|basic implementations are exemplified among the actual products of
|evolution, and one of them was arrived at twice independently
|(biologists: am I correct that insect vision is basically different
|from vertebrate vision, but that octopus vision is fairly similar? --
|I'm willing to fall back to 3 independent implementations).

It depends somewhat on what you mean by `basic implementations'.
Insect vision is certainly based on different "engineering" principles
than vertebrate vision (though it still uses lenses, so there is some
similarity, I believe that lensless vision is possible, and may even exist
in some obscure group).  The octopus eye is based on similar "engineering",
but it has a different construction - the photosensitive cells are not
adjacent to the bounding membrane like they are in vertebrates, thus
removing the problem of the light having to pass through two other layers
of cells (the ganglion cells, and the bipolar cells) before it reaches
the photsensitive cells. (That is octopus eyes are actually *better*
than ours).

No two implementations of vision are exactly identical.  And you missed
at least one `implementation', clams eyes!
-- 
sarima@teradata.com			(formerly tdatirv!sarima)
  or
Stanley.Friesen@ElSegundoCA.ncr.com


