What Do Chameleons See?

[Marat]

The human visual field is continuous, since we have binocular vision, so we see one integrated world, fading off gradually toward the periphery, with a few small scotomas within the visual field. But since a chameleon can rotate its eyes, which lie on opposite sides of its head, independently and with a large degree of freedom, what does it see and how does it integrate its experience into a coherent awareness of a single world, especially when the left eye is looking downwards and the right eye is looking upwards? Does it see two discontinuous worlds at the same time, which it somehow 'conceptually' manages to weave into a coherent world picture, even though it is not imagistically coherent? If it had the intelligence of a human, could it read the New York Times with its left eye looking down while simultaneously reading and understanding Grimm's Fairy tales which it was reading with the right eye looking up?

[CharonY]

Well, it is able to react to anything in either part of its vision. I am only speculating here (thought there should be info around somewhere) but chances are that eye positioning will be part of the information sent to the brain to interpret the visual cues. The overall impression it has is likely similar to us humans, lacking sensory info is glossed over in the brain.

 

Regarding is a bit more complicated compared to just seeing things. The interpretation of the written words usually requires quite a bit of focus. Unless the hypothetical chameleon would a have specialized area each able to read independently the ability to see incoherent views will not allow it to read (but theoretically it could switch from reading with one eye to reading with the other in fast succession).

[lemur]

My guess would be that it focuses on seeking prey with whichever eye it catches first glimpse of that prey. Maybe it is able to focus with both eyes for depth triangulation when necessary. Otherwise, I think it seems handy to keep the other eye at a different angle to check for threats - like extended (active) peripheral vision. If a chameleon could read, I think it would use one eye to read and the other to watch out for threats and potential prey (or mating opportunities), the same way reading-humans use their peripheral vision and other senses to pay attention to such things.

[Marat]

I guess from my human perspective I am having trouble visualizing what the chameleon actually perceives in its brain. It is tempting but misleading to think it must have a central eye behind the two independently targeted eyes which generate two discontinuos visual fields, so that it sees two separate screens at once, one to the left and the other to the right. But of course there is no unified visual field behind the two discrete ones, so somehow as it is getting impressions from each eye independently, it can infer how these visual fields relate to each other in the space outside it. But just as a lot of additional brain power evolved in human ancestors when these creatures adopted a spatially complex, arboreal existence, it would seem that the chameleon would need a lot of brain space just to integrate relations between the two independent visual fields, which would be quite a complex task, given that the fields move frequently and are constantly shifting orientation, both with respect to the outside world and to each other. However, the brain of the chameleon is tiny, so how does it manage this?

[CharonY]

Often one does not need a lot of structure or mechanisms to integrate information, if it is already encoded withing the signal itself, if that makes any sense. For instance,if the brain also gets eye movement information (which it does) it can easily pinpoint the visual field relative to the body position, without the need of extensive reconstruction. In fact even in humans the continuous perception is largely an illusion. Split brain experiments are an example, for instance. The individuals with their pons damaged still perceive things as continuous, though in truth they have two non-interacting visual fields.

Edited October 4, 2010 by CharonY

[Marat]

That seems more sensible than the alternative explanation, which is that the chameleon has an eye behind its eyes, which views two separte windows, above which it can read the labels 'left' and 'right.' Thanks!

[Maximus Semprus Veridius]

Yeah good question I have wondered what it would "look like" to have chameleon vision. I think that they search for prey primarily with BOTH eyes scanning their surrounding environment then they use both eyes to focus on their victim. I think it would need special parts in the brain to effectively read two things just as though they were reading and understanding one. I imagine that it could be compared to having two pages flashing quickly in succession of one another, as a human you would naturally just read one of the two pages.

[Marat]

I have a Jacksonian chameleon at home and have been trying primitive experiments with it. If I dangle a meal worm in front of its left eye and then rotate the worm around in front of the chameleon's snout and into its blind spot, the right eye will already start to move towards the area into which the worm has moved, even though it can't see it. So I am assuming there is some brain-driven operation going on here to secure as much continuity of the visual fields as possible in order to keep tracking the worm. This may be like our own instinctive turning toward the flashing of something on the very periphery of our vision.

 

A problem with all the experiments I have tried moving the worm in and out of the visual fields from various angles is that this has to be done close enough to the chameleon to ensure that he is not seeing the worm with both eyes at once, as it could at a distance. But then the worm comes within the smelling range of the chameleon, so it may be relying on olfactory data for its responses. If the chameleon weren't a pet, the thing to do would be surgically to destroy its olfactory nerves and then repeat these experiments.

[Thelemaway]

http://evans-experientialism.freewebspace.com/nagel.htm

 

This kind of answers the question, but not in a good way.