Detecting Motion and Color

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Students will understand how the photoreceptors in their eyes detect motion and color.

Big Idea

Students will understand that motion and color are detected by different parts of the eye and in very specific regions of the visual field.

RAP - Review and Preview

5 minutes

I call students to the gathering area. We review the color observations we made in our previous lesson. I tell students that we now understand how color is made using white light and breaking it apart. However, the question remains, how do our eyes process color and motion? 


I show students a diagram of an eye. I remind them that we have dissected a cow’s eye in a previous unit. See lesson 1 and lesson 2 where we dissected a cow’s eye and discussed its structure and function. We review the different parts of the eye and how it processes light as information. 

Guided Investigation

30 minutes

I tell students that today we are going to test the function of their photoreceptors. We’re going to look at how they work and where along the retina they are located. I tell students that they will work in pairs. They will conduct the experiment twice with one person as the test subject and one as the scientific investigator, and then vice versa.

Each pair of students will receive a poster board (28” x 20”), a meter stick, and a sharpie. They will draw, near the top of the long side of a poster board, a line. At the center point on the board they will mark 0 degrees. Making sure that you are using a 28” poster board, each inch from the center will equal 10 degrees.

Once students have created their board, I hand them three circles of different colored paper, about the size of a nickel. They attach these to the end of three different rulers.

 (See instruction sheet)

One student acts as the test subject and one as the investigator. The test subject should hold the cardboard in a semi-circle in front of his/her face, with the edges of the poster at his/her ears. The poster board should be about 12 inches from the test subjects face.

The investigator, passes the color dot from the ear around the top edge of the cardboard toward the subjects nose. The subject focuses only on the zero degree mark and notes when he/she can see the object in his/her peripheral vision. The investigator should make a mental note of the angle at which this occurs. The investigator then continues to move the stick until the subject can tell the color of the dot. The investigator makes note of the angle that this occurs. The investigator writes down both these results. The investigator should repeat this process from the other side of the subject’s head with a different color stick. The investigator should ensure that the subject does not know the color of the dot being used.

(See instruction sheet)

Students switch roles and complete the experiment a second time, recording both sets of results.

Wrap Up

10 minutes

Once students have completed their experiments both times, I hand them two question stems to answer on the Reflection section of their observation sheets.

The stems are:

  1. Why do I sense motion before I see color?
  2. Why do we believe that we see color all throughout our field of vision, and not just in a small focused area, if in fact, we can only see color in our central visual field?

I don't answer these questions for students as I want them to wonder about them as they leave the class for the day. this will stimulate thought and wonder, which are important habits of mind for scientists to develop. They also need to learn to deal with not always having the answer given to them immediately, as this is something that is prevalent in scientific inquiry.