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Old 09-09-2017, 03:25 AM   #1
Ottriman
 
Join Date: Apr 2015
Default What if you replaced all cones with rods?

This is about vision, I am writing a novel and might also use this for a game at some point.

A character has a power that lets her transform her eyes to replace all the cones with more rods to sacrifice color vision in favor of night vision. We'll assume no neurology problems or anything from this.

1) How many levels of the Night Vision advantage would that be?

2) If she also added the eye-mirror thing into her eyes that a cat has, how would that affect things. Again we assume no compatability issues.

3) How would you stat this? Something like Night Vision X (Switchable, temporary disad: colorblindness) right?

Edit: 4) What would this look like?
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Old 09-09-2017, 05:10 AM   #2
malloyd
 
Join Date: Jun 2006
Default Re: What if you replaced all cones with rods?

Quote:
Originally Posted by Ottriman View Post
This is about vision, I am writing a novel and might also use this for a game at some point.

A character has a power that lets her transform her eyes to replace all the cones with more rods to sacrifice color vision in favor of night vision. We'll assume no neurology problems or anything from this.
You are completely restructuring the nerves and visual cortex of your brain, but for some reason keeping the density of receptors on your retina the same? Why? Shouldn't you consider increasing them instead?

Quote:
1) How many levels of the Night Vision advantage would that be?
Less than you probably think. You have about 10% as many cones as rods, but rods are about two orders of magnitude more sensitive, so in principle you get about 10 times the light response. But 10 times the brightness isn't all that much by the standards of variation of light levels eyes function in. It's less than +2.

Quote:
2) If she also added the eye-mirror thing into her eyes that a cat has, how would that affect things. Again we assume no compatability issues.
Not much here either. This basically just gives you a second chance to detect a particular photon that missed the first time (and a cost of blurring the focus of it I suppose). Doubling the light intensity is less than a +1 (about +0.43 for the log ratios).

The fact is human vision (and hearing and touch) are quite good as animals go, and smell isn't bad, particularly for the stuff primates specialize in - we're actually pretty amazing at smelling esters ("fruit flavors"). We tend to exaggerate how fantastic animal senses are.

Quote:
3) How would you stat this? Something like Night Vision X (Switchable, temporary disad: colorblindness) right?
Sounds right to me.

Quote:
Edit: 4) What would this look like?
Changing cones to rods is probably invisible without instruments, though maybe somebody with a flashlight peering into your pupil could notice something. A reflective layer is only really obvious in the dark in situations if whoever is looking at you is standing along the line between you and a light source brighter than the ambient light (i.e. pretty much only when the observer is a human carrying or standing in an area of artificial light), but can occasionally glint in moonlight too.
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Old 09-09-2017, 05:16 AM   #3
Ottriman
 
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Default Re: What if you replaced all cones with rods?

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Originally Posted by malloyd View Post
You are completely restructuring the nerves and visual cortex of your brain, but for some reason keeping the density of receptors on your retina the same? Why? Shouldn't you consider increasing them instead?


Less than you probably think. You have about 10% as many cones as rods, but rods are about two orders of magnitude more sensitive, so in principle you get about 10 times the light response. But 10 times the brightness isn't all that much by the standards of variation of light levels eyes function in. It's less than +2.



Not much here either. This basically just gives you a second chance to detect a particular photon that missed the first time (and a cost of blurring the focus of it I suppose). Doubling the light intensity is less than a +1 (about +0.43 for the log ratios).

The fact is human vision (and hearing and touch) are quite good as animals go, and smell isn't bad, particularly for the stuff primates specialize in - we're actually pretty amazing at smelling esters ("fruit flavors"). We tend to exaggerate how fantastic animal senses are.



Sounds right to me.



Changing cones to rods is probably invisible without instruments, though maybe somebody with a flashlight peering into your pupil could notice something. A reflective layer is only really obvious in the dark in situations if whoever is looking at you is standing along the line between you and a light source brighter than the ambient light (i.e. pretty much only when the observer is a human carrying or standing in an area of artificial light), but can occasionally glint in moonlight too.
Right, so I should come up with a different explanation for her ability to shift into a black-white night vision mode. Thank you for educating me.
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Old 09-09-2017, 06:20 AM   #4
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Default Re: What if you replaced all cones with rods?

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Originally Posted by malloyd View Post
Not much here either. This basically just gives you a second chance to detect a particular photon that missed the first time (and a cost of blurring the focus of it I suppose). Doubling the light intensity is less than a +1 (about +0.43 for the log ratios).
My understanding is that the tapetum lucidum causes cats vision to permanently look like there's petroleum jelly on the camera lens, if you will. This, combined with some other factors [1] mean that cats see better than a non-sight-hunting dog [2] but they still see pretty crap by human standards and the tapetum lucidum is a significant factor.

Eyeshine is cool looking though, so if you want a character to have it and plausibly not have a permanent kinda blurry vision (which would be an interesting character flaw) you could wave your hands around with something about enhanced post-processing being done in the visual cortex.

[1] They have other focal oddities caused by the slit pupil, and of course their muzzle forms a gigantic blind spot in their FOV (they use their whiskers to compensate for that).

[2] Standard poodles are sight hunters, for example, and have better distance vision than cats, and don't have the slit pupil focal funkyness. But the long muzzle forms an even more gigantic blind spot.
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Old 09-09-2017, 07:15 AM   #5
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Default Re: What if you replaced all cones with rods?

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My understanding is that the tapetum lucidum causes cats vision to permanently look like there's petroleum jelly on the camera lens, if you will. This, combined with some other factors [1] mean that cats see better than a non-sight-hunting dog [2] but they still see pretty crap by human standards and the tapetum lucidum is a significant factor.
The primary issue, though, is that the density of photoreceptors on the retina is less. In human terms, most mammals have vision that's not much better than 20:200. (Or, in GURPS terms, human vision is Discriminatory.) The blurring effect of the tapetum lucidum is nontrivial but doesn't mess things up as badly as the low-density retina. And it might be less significant for cats precisely because their receptors are farther apart, so a double image that would seriously mess up human vision might not count for much for feline vision.
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Old 09-09-2017, 12:42 PM   #6
Anthony
 
Join Date: Feb 2005
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Default Re: What if you replaced all cones with rods?

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Originally Posted by Ottriman View Post
1) How many levels of the Night Vision advantage would that be?
Basically zero, the night vision rules already assume in extreme darkness you're only using rods, so you've got maybe a factor of 2.
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Old 09-09-2017, 02:06 PM   #7
Fred Brackin
 
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Default Re: What if you replaced all cones with rods?

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Originally Posted by Bruno View Post
Eyeshine is cool looking though, so if you want a character to have it and plausibly not have a permanent kinda blurry vision (which would be an interesting character flaw) you could wave your hands around with something about enhanced post-processing being done in the visual cortex.
This might be one of those things better done with tech. For example if you've got "smart matter" and nanites to implant it you could put a layer behind the retina that's able to switch it from reflective to dark.

UT already has image processing. It's hidden as a computer program on p.56.

The Gurps rules are unhelpful in some respects. For example, if ever given a choice between equal levels of Acute Vision and Night Vision take the Acute Vision every time. It is twice as expensive but it's probably more than twice as useful.

If it would be helpful to know, Bio-tech allows NV 2 to genetically normal humans and 5 for maximum biological modification. Acute Vision is 3 levels and 5 respectively. Tactical Shooting won't go for more than Acute Vision 2 though.
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Old 09-09-2017, 02:28 PM   #8
malloyd
 
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Default Re: What if you replaced all cones with rods?

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Originally Posted by Fred Brackin View Post
The Gurps rules are unhelpful in some respects. For example, if ever given a choice between equal levels of Acute Vision and Night Vision take the Acute Vision every time. It is twice as expensive but it's probably more than twice as useful.
Actually not. Acute Vision adds to your Sense rolls. Night Vision *negates penalties*. This is an important difference, Acute Vision doesn't do anything to reduce the penalties you suffer for combat in low light, Night Vision does. If your GM ever applies penalties for doing something in bad light, as many levels of Night Vision as he'll let you buy is almost a no brainer.
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Old 09-09-2017, 03:09 PM   #9
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Default Re: What if you replaced all cones with rods?

A special effect that is obviously different between placental mammals and marsupial mammals is the colour of the light that is reflected when a light source is directed at the eyes. A subtle bit of flavour for a change to the structure if the eyes.
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Old 09-09-2017, 03:26 PM   #10
Anthony
 
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Default Re: What if you replaced all cones with rods?

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Originally Posted by Fred Brackin View Post
It is twice as expensive but it's probably more than twice as useful.
It's twice as expensive and less useful. Keen eyes is effectively +1 perception (visual). Night vision is effectively +1 DX and IQ, only in situations of partial darkness.
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