1. Vision Module 13
Psychology 7e in Modules

2. Vision Vision The Stimulus Input: Light Energy The Eye
Visual Information Processing
Color Vision
Psychology 7e in Modules

3. Conversion of one form of energy to another.
Transduction
Conversion of one form of energy to another.
How is this important when studying sensation?
Stimulus energies to neural impulses.
For example:
Light energy to vision.
Chemical energy to smell and taste.
Sound waves to sound.

4. Vision

5. The Stimulus Input: Light Energy
Visible
Spectrum
Both Photos: Thomas Eisner

6. What makes up a light wave?

7. Light Characteristics
Wavelength (hue/color)
Intensity (brightness)
Saturation (purity)

8. Hue (color): dimension of color determined by wavelength of light.
Wavelength (Hue)
Hue (color): dimension of color determined by wavelength of light.
Wavelength the distance from the peak of one wave to the peak of the next.

9. Different wavelengths of light result
Wavelength (Hue)
Violet
Indigo
Blue
Green
Yellow
Orange
Red
400 nm
700 nm
Short wavelengths
Long wavelengths
Different wavelengths of light result
in different colors.

10. Intensity (Brightness)
Intensity Amount of energy in a wave determined by amplitude; related to perceived brightness.

11. Intensity (Brightness)
Blue color with varying levels of intensity.
As intensity increases or decreases, blue color
looks more “washed out” or “darkened.”

12. Purity (Saturation) Monochromatic light added to green and red
Saturated
Saturated
Monochromatic light added to green and red
make them less saturated.

13. Represents all three characteristics of light stimulus on this model.
Color Solid
Represents all three characteristics of light stimulus on this model.

14. The Eye
OBJECTIVE 13-2| Describe the major structure of the eye, and explain how they guide the incoming ray of light toward the eye’s receptor cells.
Psychology 7e in Modules

15. Cornea
Pupil/Iris
Lens: accommodation
Retina/rods and cones (fovea)
Bipolar cells -> ganglion cells
Optic nerves
Where they cross is the optic chiasm
Thalamus
Occipital lobe

16. Fig. 5.4 The human eye, a simplified view.
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17. Fig. 5.6 The iris and diaphragm.
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18. Parts of the eye
Cornea: Transparent tissue where light enters the eye.
Iris: Muscle that expands and contracts to change the size of opening (pupil) for light.
Lens: Focuses the light rays on the retina. Accommodation
Retina: Contains sensory receptors that process visual information and send it to the brain.

19. Light Control (cont.) Visual Acuity: Sharpness of visual perception
Fovea: Area of the retina containing only cones
Peripheral Vision: Vision at edges of visual field; side vision
Many superstar athletes have excellent peripheral vision
Tunnel Vision: Loss of peripheral vision
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20. Light Control
Cones: Visual receptors for colors and bright light (daylight) Fine detail vision
Rods: Visual receptors for dim light; only produce black and white
Blind Spot: Area of the retina lacking visual receptors
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21. The Lens
Lens: Transparent structure behind pupil that changes shape to focus images on the retina.
Accommodation: The process by which the eye’s lens changes shape to help focus near or far objects on the retina.

22. The Lens
Nearsightedness: A condition in which nearby objects are seen more clearly than distant objects.
Farsightedness: A condition in which faraway objects are seen more clearly than near objects.

24. Nearsighted Vision

25. Farsighted Vision

26. Retina
Retina: The light-sensitive inner surface of the eye, containing receptor rods and cones plus layers of other neurons (bipolar, ganglion cells) that process visual information.
OBJECTIVE 13-3| Contrast the two types of receptor cells in the retina, and describe the retina’s reaction to light.
Psychology 7e in Modules

27. Optic Nerve, Blind Spot & Fovea
Optic nerve: Carries neural impulses from the eye to the brain. Blind Spot: Point where optic nerve leaves the eye, because there are no receptor cells located here, it creates a blind spot. Fovea: Central point in the retina, around which the eye’s cones cluster.

29. Photoreceptors
E.R. Lewis, Y.Y. Zeevi, F.S Werblin, 1969

30. Bipolar & Ganglion Cells
Bipolar cells receive messages from photoreceptors and transmit them to ganglion cells, which form the optic nerve.

31. Visual Information Processing
Optic nerves connect to the thalamus in the middle of the brain, and the thalamus to the visual cortex.
OBJECTIVE 13-4| Discuss the different levels of processing that occur as information travels from the retina to the brain’s cortex.
Psychology 7e in Modules

32. Ganglion & Thalamic Cells
Retinal ganglion cells and thalamic neurons break down visual stimuli into small components and have receptive fields with
center-surround organization.
ON-center OFF-Surround
Action Potentials

33. Feature Detection
Nerve cells in the visual cortex respond to specific features, like edges, angle, and movement.
Ross Kinnaird/ Allsport/ Getty Images

34. Shape Detection
Specific combinations of temporal lobe activity occur as people look at shoes, faces, chairs and houses.
Ishai, Ungerleider, Martin and Haxby/ NIMH

35. Perception in Brain
Our perceptions are a combination of sensory (bottom-up) and cognitive (top-down) processes.

36. Visual Information Processing
Processing of several aspects of the stimulus simultaneously is called parallel processing. The brain divides a visual scene into subdivisions such as color, depth, form and movement etc.
OBJECTIVE 13-5| Discuss parallel processing and discuss its role in visual processing.
Psychology 7e in Modules

37. Parallel Processing
The processing of several aspects of a problem simultaneously.
Motion
Form
Color
Depth

38. How do we see in color?
What color is this dragon?

39. Color The dragon is anything but red.
The dragon rejects the long wavelengths of light that to us are red- so red is reflected of and we see it.
Also, light has no real color.
It is our mind that perceives the color.

40. From Sensation to Recognition
Tim Bieber/ The Image Bank

41. Color Vision
Trichromatic Theory: Color vision theory that states we have three cone types: red, green, blue
Other colors produced by a combination of these
Black and white produced by rods
Opponent Process Theory: Color vision theory based on three “systems”: red or green, blue or yellow, black or white
Exciting one color in a pair (red) blocks the excitation in the other member of the pair (green)
Afterimage: Visual sensation that remains after stimulus is removed (seeing flashbulb after the picture has been taken)
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42. Young-Helmholtz Trichromatic (three color) Theory
Realized that any color can be created by combining the light waves of three primary color-
RED
GREEN
BLUE
So they guessed that we have 3 different types of receptor cells in our eyes. Together they can pick any combination of our 7 million color variations.
Most colorblind people simply lack cone receptor cells for one or more of these primary colors.

43. Subtraction of Colors
If three primary colors (pigments) are mixed it results in subtraction of all wavelengths and the result is a black color.

44. Addition of Colors
If three primary colors (lights) are mixed the wavelengths are added and they result in white color.
Fritz Goro, LIFE magazine, © 1971 Time Warner, Inc.

45. Photoreceptors
Blue
Cones
Green
Cones
Red
Cones
MacNichol, Wald and Brown (1967) measured directly the absorption spectra of visual pigments of single cones obtained from the retinas of humans.
Short
wave
Medium
wave
Long
wave

46. Color Blindness
Inability to perceive colors; lacks cones or has malfunctioning cones
Total color blindness is rare
Color Weakness: Inability to distinguish some colors
Red-green is most common; much more common among men than women
Recessive, sex-linked trait on X chromosome
Ishihara Test: Test for color blindness and color weakness
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47. Color Blindness
Genetic disorder in which people are blind to green or red colors supports Trichromatic theory.
Ishihara Test

48. Fig. 5. 15 Color blindness and color weakness
Fig Color blindness and color weakness. (a) Photograph illustrates normal color vision. (b) Photograph is printed in blue and yellow and gives an impression of what a red-green color-blind person sees. (c) Photograph simulates total color blindness. If you are totally colorblind, all three photos will look nearly identical.
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49. Dark Adaptation
Increased retinal sensitivity to light after entering the dark; similar to going from daylight into a dark movie theater
Rhodopsin: Light-sensitive pigment in the rods; involved with night vision
Night Blindness: Blindness under low-light conditions; hazardous for driving at night
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50. Opponent Process Theory
Hering, proposed that we process four primary colors opposed in pairs of red-green, blue-yellow, and black-white.
Cones
Retinal
Ganglion
Cells

51. Fig. 5. 11 Negative afterimages
Fig Negative afterimages. Stare at the dot near the middle of the flag for at least 30 seconds. Then look immediately at a plain sheet of white paper or a white wall. You will see the American flag in its normal colors. Reduced sensitivity to yellow, green, and black in the visual system, caused by prolonged staring, results in the appearance of complementary colors. Project the afterimage of the flag on other colored surfaces to get additional effects.
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52. Fig Firing rates of blue, green, and red cones in response to different colors. The taller the colored bar, the higher the firing rates for that type of cone. As you can see, color sensations are coded by activity in all three types of cones in the normal eye. (Adapted from Goldstein, 1999.)
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53. Opponent-Process Theory
We cannot see certain colors together in combination (red-green, blue-yellow, and white-black). These are antagonist/ opponent colors.
Tube and marble example.

55. Color Constancy
Color of an object remains the same under different illuminations. However, when context changes color of an object may look different.
OBJECTIVE 13-7| Explain the importance of color constancy.
R. Beau Lotto at University College, London
Psychology 7e in Modules