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Why are our eyes tuned to a specific band of the EM spectrum?

  1. Mar 31, 2013 #1
    I mean why is it that the eye evolved to detect "visible" light instead of, say, microwaves. What is it about the visible light spectrum?
  2. jcsd
  3. Mar 31, 2013 #2


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    There is one part physics of how detectors operate and another of what ambient em energy is available and useful.

    Seeing microwaves would not be that useful so it wouldn't cause evolutionary pressure. And the detector would probably be prohibitively large.
  4. Mar 31, 2013 #3


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    Staff: Mentor

    Also, notice the location of the peak of the solar radiation spectrum.
  5. Mar 31, 2013 #4


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    I'm rusty on the physics side of this but wouldn't the fact that the wavelengths of visible light are of comparable size to biomolecules have an effect?

    Also it's worth bearing in mind that perception of infrared, UV and more/less colour fidelity have been selected for in various species.
  6. Apr 1, 2013 #5
    Oh that would be nice if we can see harmful radiation. Snakes can see infrared, why cant we right. Something for me to look up.
  7. Apr 1, 2013 #6
    It's mainly because of the "optical window" of light that can pass through our atmosphere. UV, and IR-microwave penetration is largely truncated at the surface of the earth, and sensitivity to radio waves in our visual system would not give us a very detailed perspective of our surroundings.


  8. Apr 1, 2013 #7
    There may be a little ambiguity regarding electromagnetic radiations especially in the case of low frequency electromagnetic radiation. Radio waves, microwaves and far infrared radiation may be sensed by a variety of methods that don’t involve the eyes.

    There are many ways of detecting electromagnetic radiation that don’t involve the eyes. However, I am not sure whether you are asking about “detection alone. You are probably thinking about imaging. Short wavelength electromagnetic radiation is more easily imaged than long wavelength

    There are two types of sensors used by many animals that can arguably be called low frequency electromagnetic detectors. These methods can be used by some animals to form an image of a distant object. I present electroreception as a means of sensing and imaging radio waves. I present thermoreception as a means of sensing and imaging infrared waves.

    1) Electroreception is a very important sense for many animals. The vast majority of them are aquatic, since what the animal is actually sensing is electric current. Sharks in general have a very keen electroreception. However, there are bony fish that have great electroreception. Electric eels, electric catfish and knife fish have an active electroreception.

    The frequencies involved in electroreception would be radio waves. Of course, they would be miles long.

    I am not sure of the frequency band width for electroreception. I know that electric eels can generate electric pulses every that are 50 milliseconds wide and 10 seconds apart. I think they can modulate their electric current in a range frequencies corresponding to these periods of time.

    Electroreception in terrestrial animals is much rarer. However, there are some animals that can do it. These would correspond to radio waves.

    Here is a link to a general article on electroreception.
    “Electroreception is the biological ability to perceive natural electrical stimuli. It has been observed almost exclusively in aquatic or amphibious animals, since water is a much better conductor than air. Electroreception is used in electrolocation (detecting objects) and for electrocommunication.”

    A related issue is electrocommunication. Animals can’t do electrocommunication without electroreception. I found this link that mentions terrestrial animals that use electroreception in their communication. I know that most of the terrestrial animals listed spend some time in the water. However, the echidna is an exception. It doesn’t spend much time in the water.

    “Terrestrial animals, with very few exceptions, lack this electric sensing channel due to low conductivity of air, soil, or media other than aqueous environment. Exceptions include the Australian monotremes, i.e. the echidna which eats mainly ants and termites, and the semi-aquatic platypus that hunts by utilizing electric fields generated by invertebrate prey.”

    Note that these animals get very precise spatial information from their electroreception. However, electroreception is a very low frequency method of obtaining information. It is not good for fast communication. It is also a rather short range sense. This may be why electroreception isn’t universal among animals.

    2) Thermoreception is also a very important sense in many animals. Now heat can often be sensed by touch. However, heat is often transmitted through infrared radiation. When one sits near a fire to keep warm, one is absorbing heat mostly through radiative transfer.

    Thermoreception is very more common among terrestrial animals. Even humans have some form of thermoreception. However, humans can’t construct images at a distance from an objects heat signature. Snakes and other animals appear to be able to.

    Here are some links to thermoreception.
    Thermoception or thermoreception is the sense by which an organism perceives the rate of heat flux.[1] The details of how temperature receptors work are still being investigated. Ciliopathy is associated with decreased ability to sense heat, thus cilia may aid in the process.[2] Transient receptor potential channels (TRP channels) are believed to play a role in many species in sensation of hot, cold, and pain. Mammals have at least two types of sensor: those that detect heat (i.e., temperatures above body temperature) and those that detect cold (i.e. temperatures below body temperature).[citation needed]
    A particularly specialized form of thermoception is used by Crotalinae (pit viper) and Boidae (boa) snakes, which can effectively see the infrared radiation emitted by hot objects.[3] The snakes' face has a pair of holes, or pits, lined with temperature sensors. The sensors indirectly detect infrared radiation by its heating effect on the skin inside the pit. They can work out which part of the pit is hottest, and therefore the direction of the heat source, which could be a warm-blooded prey animal. By combining information from both pits, the snake can also estimate the distance of the object.
    The common vampire bat Desmodus rotundus has specialized infrared sensors in its nose-leaf.[4][5] Vampire bats are the only mammals that feed exclusively on blood. The infrared sense enables Desmodus to localize homeothermic (warm-blooded) animals (cattle, horses, wild mammals) within an range of about 10 to 15 cm. This infrared perception is possibly used in detecting regions of maximal blood flow on targeted prey.”

    I notice that snakes and vampire bats get very good directional information from the heat signatures of their prey. That is what I am referring to as imaging. Furthermore, they are not obtaining the heat by heat conduction or convection. They are using the infrared radiation. Hence, I propose that this may be what you are looking for with respect to infrared radiation.
  9. Apr 8, 2013 #8
    One factor may be the sensor size. As you go down frequency from optical frequencies sensors tend to become bigger because the wavelength gets longer. Go up frequency, and the sensors get larger because the photons take longer to stop. Near-infra-red to ultraviolet tend to make the smallest sensors, which leads to the highest resolution.
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