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From: john larkin <JL@gct.com>
Newsgroups: sci.electronics.design
Subject: Re: Nerve cells in blind mice retain their visual function
Date: Fri, 29 Nov 2024 11:18:47 -0800
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On Fri, 29 Nov 2024 12:16:54 -0600, Crash Gordon <uucp@crashelex.com>
wrote:

>On 11/29/2024 3:04 AM, Liz Tuddenham wrote:
>> I recently heard that the presence of a third type of photoreceptor cell
>> has been detected in the human eye.  As well as rods and cones, there is
>> a more primitive light-sensitive mechanism for setting the body clock.
>
>I was recently in the room with a relative who was being tested with an 
>unusual method.  They were asked to look at a target, close their eyes, 
>and then touch the target.  They missed by several inches.  Then the Dr. 
>would put a colored filter in front of their eyes *after* the eyes were 
>closed -- and certain colors would improve their ability to find the 
>target.  I would not have believed it if I had not watched it personally.
>
>There's a video of the technique here:
>https://www.youtube.com/watch?v=qA_tjGCFzgg
>using a ringing bell instead of a visual target.  The video doesn't 
>point out that the test is done with eyes closed, but it is.
>
>It takes several weeks to adjust to wearing the special glasses that are 
>prescribed; at first my relative could only wear them for two or three 
>minutes lying down in a dark room with eyes closed, before feeling 
>dizzy.  After a month or so they had built up to the point of being able 
>to wear them all day.  And the glasses* were a big help in treating 
>their symptoms.
>
>I asked the Dr. how colored lenses could have any effect on closed eyes, 
>and they said that there are pathways from eye to brain that are very 
>sensitive to light but do not connect to the visual cortex.  It's pretty 
>amazing to see it in action.
>
>=====
>*BTW the colored filters are used only for diagnostic purposes.  The 
>glasses themselves are not colored.

I can sense hot objects in a room by skin feel, thermal IR receptors
of some sort. Directionality is poor.