A Little Bit More
Since humans see color, it’s hard for us to imagine that other animals may see differently. Many other animals, particularly mammals, are less vision-oriented and use other senses (touch, smell, and hearing) to a much greater extent than we do. Visual perception (what we can or can’t see) is biologically important and appears to be related to specific problems and conditions in an animal’s environment that animals are adapted for.
Rods and cones are the photoreceptor (light-sensitive) cells in the eye that permit vision. The rods provide vision in dim light and are abundant in nocturnal animals. Cones are used for bright-light vision and are the most important receptors for color vision. Although all vertebrates appear to have at least some cone cells, these do not all respond to different colors in the same way.
Although color vision appears to exist in most insects (some can see ultraviolet light too), fishes, reptiles, and birds, it is not present to any great degree in mammals, with the exception of primates – lucky us. Amphibians do not seem to have a great degree of color discrimination either, even though some, especially salamanders, are quite colorful.
Activities
Science – Can You Read This?
Objectives: Experience how our eyes function in dim light
Materials: Materials: Text in book, newspaper or whatever
This activity needs to be undertaken at dusk when daylight is fading.
1. Sitting next to a window before dusk, hold some printed material in your hands.
2. Note the colors of various articles around you in the room and read a portion of the text. Be sure to note how easily you’re able to read the text.
3. As the light fades, continue to monitor the colors in the room and from time to time, look at the text to see how easy it is to read “now”.
4. At some point as the light continues to fade, you should begin to notice that you’re not able to distinguish some or all of the colors in the room, as earlier, and that the text is more and more difficult, if not impossible, to read.
As the light faded, your color-sensitive cone cells (you have many of these) were less and less able to respond, affecting your ability to see colors in the room and reading the text you were reading. Although the light faded, you were still able to see, but you were now relying more and more on your light-sensitive rod cells (you have fewer of these) in the dim light. As a result, the text became harder and harder to read, not because the light was dim, but because you had switched to a visual system that relies on your more widely scattered rod cells. Simply put, you can’t read in dim light because you can’t pick up closely packed details with widely spaced rod cells.
It should be noted that younger participants will probably be better able to read well into the darker dusk than older participants. Our eyesight is at its best around 10 years of age and then slowly deteriorates after that. So, if you have a 10 year old and a 50 year old doing this exercise together, there is likely to be a BIG difference in what can and can’t be seen as the light fades.
Inquiry activity you may want to pursue: Since we’ve mentioned that younger people usually have better vision than older ones, it would be interesting to assemble several people of various ages and see what they can and cannot see in dim light. In a poorly lit room, will the 50 year old person be able to see the print on the newspaper as well as the 10, 20 or 30 year old? Try it and see.
Key Concepts
Structures and Functions, Adaptations and Diversity
Questions
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