A study conducted at the Technion and the University of Haifa reveals how the chameleon overcomes its narrow field of vision by turning its head
Prof. Ehud Rivlin from the Faculty of Computer Science at the Technion
One of the variables that differentiates different animals is their field of vision, which is dictated by the position of the eyes and their range of motion. Man, for example, is characterized by a rather narrow field of vision, for which he compensates by turning his head in the desired direction. The man, whose angle of vision is even narrower, covers this up by being able to turn his head more than a full turn without changing his body position. The chameleon, on the other hand, enjoys an incredibly wide field of vision as well as the ability to turn each eye in a different direction. Through this "voluntary squinting" the chameleon saves head and body movements that might betray it to its enemies and prey alike.
It is customary to assume that each of the chameleon's eyes moves autonomously, that is, without connection to the other eye. A recent study conducted by Prof. Ehud Rivlin from the Technion's Faculty of Computer Science and Prof. Gadi Katzir from the University of Haifa reveals that this assumption is wrong. In a study, recently published in The Journal of Experimental Biology, the researchers examined the law that dictates the movement of the chameleon's eyes and discovered that there is a certain coordination between the two eyes.
Prof. Rivlin, who led the technical group in the research, has been researching the chameleon's visual system for many years. In a previous study he investigated and formulated the optimal scanning model of the chameleon. In the current study, the researchers, in the first step, placed a chameleon in front of a computer screen on which a virtual fly flies. Every time the chameleon saw the fly, she "locked" both of her eyes on him, measured the distance between her and him, and then attacked - as was already known from the previous study.
In the second phase of the new experiment, the researchers "cut" the virtual fly in two, and moved each of the halves in a different direction. Now the chameleon was required to follow a different part of the fly with each eye. However, since she only had one tongue, the chameleon had to choose which half to attack. In the current experiment, it was discovered that indeed, the chameleon looked at both halves for a while at the same time - each eye focused on one of them - but as soon as it chose one of the halves, it locked both eyes on it to gauge the distance before the attack.
"Our conclusion is that the chameleon's eyes are not completely independent of each other as is commonly thought," says Prof. Rivlin. "At any given moment, each eye is aware of the position and direction of the other eye. In other words, even in the monocular vision that characterizes the chameleon, there is a certain cooperation - just as another cooperation exists in the binocular vision of man."
For the full article: http://jeb.biologists.org/content/218/13/2097.short
2 תגובות
Tikun - focuses both her eyes on him.
1. Why was it necessary to "cut" the fly in half, wasn't it simpler to present two separate flies?
2. I did not understand how from the above experiment the researchers came to the conclusion that until the moment of "locking" the eyes do not work independently? After all, even before that they knew that as soon as the chameleon detects a nearby prey, it focuses both of its eyes on it, so what is the innovation here that they didn't know about before?