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Offline science_guy

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Night Vision
« on: 16/05/2007 15:47:15 »
Why are a nocturnal animal's eyes shiny at night, and how does this help them see?


 

Offline tony6789

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« Reply #1 on: 16/05/2007 16:42:19 »
it has something to do wiht some kinda color cones in their eyes
 

Offline WylieE

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Night Vision
« Reply #2 on: 16/05/2007 23:28:12 »
Dogs and cats and other nocturnal animals with good night vision have a layer at the back of the eye called the tapetum.

  The light that comes in goes through the retina and some of it is absorbed by the rods.  What isn't absorbed passes through and hits the tapetum.  The tapetum is reflective and the light bounces off the tapetal layer and back through the retina a second time- so whatever didn't get absorbed the first time gets a second chance.  This allows them to collect the most light for seeing at night. 

This tapetum is what gives them the green / blue color in bright light.  Of course even on the second trip through the retina not all of the light will get absorbed if it is a bright light, so their eyes will reflect back to our eyes the excess light and they would look shiny. 

Colleen
 

another_someone

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Night Vision
« Reply #3 on: 16/05/2007 23:59:47 »
What is the price they pay for having a tapetum?  Does it give them greater problems in seeing in bright daylight, or does it make their eyes vulnerable in other ways?  In other words, why do other animals not have this layer?
 

Offline kdlynn

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« Reply #4 on: 17/05/2007 01:06:02 »
is it true that they are color blind? does that have anything to do with that layer
 

another_someone

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Night Vision
« Reply #5 on: 17/05/2007 01:38:50 »
is it true that they are color blind? does that have anything to do with that layer

Most mammals have restricted colour vision compared to primates.

One suggestion I have seen is that there is a genetic trade off between colour sensitivity and sense of smell, so we have better colour vision as a trade for having a lessened sense of smell.
 

Offline kdlynn

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« Reply #6 on: 17/05/2007 01:55:38 »
that makes sense. we can see if our food has gone bad as well as smell it, but other animals can smell it before we do but can't see discolorations
 

another_someone

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Night Vision
« Reply #7 on: 17/05/2007 02:13:57 »
that makes sense. we can see if our food has gone bad as well as smell it, but other animals can smell it before we do but can't see discolorations

Certainly, that would be part of it, but just as important is how we detect our prey when hunting, and how we communicate between outselves (we have a wide range of facial expressions and body language, but we don't go around sniffing each other as much as other animals do).

Food only really goes off if you are scavenging (it is not not clear to what extent early humans were hunters, and what extent they were scavengers).  If you are eating a fresh kill, or just recently dug something out of the soil, having the food go off is not that much of a risk, but finding the food in the first place is far more critical.

A related issue to determining whether food has gone off is determining whether food is poisonous.

At least one theory I heard was that they reason why we developed an ability to see red was to be able to detect blushing as a means of communication - not sure how seriously the theory was taken.
« Last Edit: 17/05/2007 02:17:27 by another_someone »
 

Offline kdlynn

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« Reply #8 on: 17/05/2007 02:18:20 »
funny i hadn't even thought of communication. thanks george!
 

Offline tony6789

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« Reply #9 on: 17/05/2007 16:26:22 »
blue flower red thorns!
 

Offline Ben6789

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Night Vision
« Reply #10 on: 17/05/2007 16:44:21 »
Psycho. :P
 

Offline tony6789

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Night Vision
« Reply #11 on: 18/05/2007 17:47:33 »
lol
 

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Night Vision
« Reply #11 on: 18/05/2007 17:47:33 »

 

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