Chapter 16. Wavelength and Cone Responses

Learning Objectives

cones
photoreceptor cells in the eye specialized for detailed color vision in bright light
hue
the apparent color of the light; related to wavelength
perception
organizing and interpreting information from the senses to understand its meaning
retina
light-sensitive inner surface of eye, containing rods and cones
statistic
a calculated number that summarizes important information about a distribution of scores
wavelength
the width of a light wave, measured as the distance between peaks; related to the hue (perceived color) of a light
Wavelength and Cone Responses
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Learning Objectives:

Distinguish among the three types of cones in the human retina.

Understand the relationship between the wavelength of light and the amount of neural activity generated in each type of cone.

Review

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Review

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1. Color vision is possible because the retina of each eye contains about 6 million cones divided into three types: short-wavelength "blueish" cones (B), medium-wavelength "greenish" cones (G), and long-wavelength "reddish" cones (R).

Review

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2. This graph shows the relative response of each type of cone to lights of different wavelengths in nanometers (billionths of a meter). Each type of cone reacts most strongly to light of a particular wavelength (the peak of each curve), but also responds to light above and below the optimal wavelength.

Review

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3. The brain evaluates the relative level of response from all three types of cones as it constructs a perception of the hue (apparent color) of objects. For example, the light reflected from this apple generates a stronger response from the medium-wavelength cones, so the brain perceives the apple as having a greenish hue.

Practice: Wavelength and Cone Responses

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Practice: Wavelength and Cone Responses

Drag the slider across the spectrum and observe how the response of each type of cone changes.

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Frequency
in nanometers (billionths of a meter)
Experienced hue
Below the slider is a bar graph with three bars. A blue bar represents short-wavelength or blue cones. A green bar represents medium-wavelength or green cones. A red bar represents long-wavelength or red cones. As the slider is moved from a lower frequency to a higher frequency the bars in the graph get taller to represent greater activation of the cones or shorter to represent less activation of the cones
B G R
Responsiveness of cones
B = short-wavelength cones
G = medium-wavelength cones
R = long-wavelength cones

Note that our color experience (hue) depends on the combined responses of the three types of cones.

Quiz 1

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Quiz 1

First, drag the slider to review the relationship between wavelength and the response of each type of cone. Then, answer the question below the graph. When you have chosen an answer, select the CHECK ANSWER button.

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Frequency
in nanometers (billionths of a meter)
Experienced hue
B G R
Responsiveness of cones
Select the NEXT button and move to Quiz 2.
You did not answer the question correctly. Try again.
Which wavelengths of light produce the strongest sensation of blue?
short wavelengths (400-500 nanometers)
medium wavelengths (500-600 nanometers)
long wavelengths (600-700 nanometers)

Quiz 2

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Quiz 2

Drag the slider until these three conditions are met. With all the conditions met, select the CHECK ANSWER button.

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Frequency
in nanometers (billionths of a meter)
Experienced hue
Below the slider is a bar graph with three bars: a blue bar labeled B, a blue bar labeled G, and a red bar labeled R. As the slider is moved from a lower frequency to a higher frequency the bars in the graph get taller to represent greater activation of the cones or shorter to represent less activation of the cones
B G R
Responsiveness of cones
Select the NEXT button and move to the Conclusion.
You did not drag the slider to the appropriate location. Try again.

When three things occur together—the short-wavelength cones are quiet, the long-wavelength cones are very active, and the medium-wavelength cones are slightly less active—we see "yellow."

Conclusion

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Congratulations!

You have completed the activity Wavelength and Cone Responses.