1. Myers’ PSYCHOLOGY (6th Ed)
Chapter 5
Sensation
Introduction and the Eye
James A. McCubbin, PhD
Clemson University
Worth Publishers

2. Fact vs. Falsehood
1. On a clear, dark night we can see a candle flame 30 miles away.
2. Advertisers are able to shape our buying habits through subliminal messages.
3. Constant eye movement prevents our vision from being seriously disrupted.
4. The retina of the eye is actually a piece of the brain that migrates to the eye during early fetal development.
5. If we stared at a green square for a while and then look at a white sheet of paper, we see red.
6. People who live in noisy environments are more likely to suffer from high blood pressure, anxiety, and feelings of helplessness.
7. Blind musician are more likely than sighted ones to develop perfect pitch.
8. Touching adjacent cold and pressure spots triggers a sense of wetness.
9. People who are born without the ability to feel pain usually die by early adulthood.
10. Without their smell, a cup of coffee may be hard to distinguish from a glass of red wine.

3. Sensation
a process by which our sensory receptors and nervous system receive and represent stimulus energy (information from our environment)
Perception
a process of organizing and interpreting sensory information, enabling us to recognize meaningful objects and events (what we do with the sensory information we receive)

4. Our sensory and perceptual processes work together to help us sort out complex processes

5. How do we get information?
Bottom-Up Processing
analysis that begins with the sense receptors and works up to the brain’s integration of sensory information (body to brain)
Top-Down Processing
information processing guided by higher-level mental processes
as when we construct perceptions drawing on our experience and expectations (brain to body)

6. Basic Principles Psychophysics
study of the relationship between physical characteristics of stimuli and our psychological experience of them
Light- brightness
Sound- volume
Pressure- weight
Taste- sweetness

7. Thresholds Absolute Threshold Difference Threshold
minimum stimulation needed to detect a particular stimulus 50% of the time
vision: candle flame at 30 miles on a clear dark night
Hearing: the ticking of a watch 20 ft away
Sense: a bee’s wing falling 1 cm onto our cheek
Smell: a drop of perfume in a 3 room apartment
Taste: 1 tsp of sugar in 2 gall of water
Difference Threshold
minimum difference between two stimuli required for detection 50% of the time
just noticeable difference (JND)

8. Thresholds Signal Detection Theory
predicts how and when we detect the presence of a faint stimulus (signal) amid background stimulation (noise)
assumes that there is no single absolute threshold
detection depends partly on person’s
experience
expectations
motivation
level of fatigue

9. Thresholds Subliminal25 50 75
100
Low
Absolute
threshold
Medium
Intensity of stimulus
Percentage
of correct
detections
Subliminal
stimuli
Subliminal
When stimuli are below one’s absolute threshold for conscious awareness

10. Thresholds
Weber’s Law- to perceive as different, two stimuli must differ by a constant minimum percentage
light intensity- 8%
weight- 2%
tone frequency- 0.3%
Sensory adaptation- diminished sensitivity as a consequence of constant stimulation

11. Eye Movement

12. How does Vision work? Transduction Wavelength
conversion of one form of energy to another
in sensation, transforming of stimulus energies into neural impulses
Wavelength
the distance from the peak of one wave to the peak of the next

13. What color is it? Hue Intensity
dimension of color determined by wavelength of light
Intensity
amount of energy in a wave determined by amplitude
brightness
loudness

14. The spectrum of electromagnetic energy

15. Physical Properties of Waves
Short wavelength=high frequency
(bluish colors, high-pitched sounds)
Long wavelength=low frequency
(reddish colors, low-pitched sounds)
Great amplitude
(bright colors, loud sounds)
Small amplitude
(dull colors, soft sounds)

16. Physiology of the Eye
Pupil- adjustable opening in the center of the eye
Iris- a ring of muscle that forms the colored portion of the eye around the pupil and controls the size of the pupil opening
Lens- transparent structure behind pupil that changes shape to focus images on the retina

17. Eye Anatomy

18. How Vision works
Accommodation- the process by which the eye’s lens changes shape to help focus near or far objects on the retina
Retina- the light-sensitive inner surface of the eye, containing receptor rods and cones plus layers of neurons that begin the processing of visual information

19. Vision problems Acuity- the sharpness of vision
Nearsightedness (myopia)- condition in which nearby objects are seen more clearly than distant objects because distant objects in front of retina
Farsightedness (presbyopia)- condition in which faraway objects are seen more clearly than near objects because the image of near objects is focused behind retina

20. Vision
Normal Nearsighted Farsighted Vision Vision Vision

21. Retina’s Reaction to Light- Receptors
Rods
peripheral retina
detect black, white and gray
twilight or low light
Cones
near center of retina
fine detail and color vision
daylight or well-lit conditions

22. Retina’s Reaction to Light
Optic nerve- nerve that carries neural impulses from the eye to the brain
Blind Spot- point at which the optic nerve leaves the eye, creating a “blind spot” because there are no receptor cells located there
Fovea- central point in the retina, around which the eye’s cones cluster

24. Vision- Receptors Receptors in the Human Eye Cones Rods Number
Location in
retina
Sensitivity in
dim light
Color sensitive?
Yes
Low
Center
6 million No
High
Periphery
120 million

25. Pathways from the Eyes to the Visual Cortex

26. Illusory Contours

27. Visual Information Processing
Parallel Processing
simultaneous processing of several aspects of a problem simultaneously

29. Visual Information Processing
Trichromatic (three color) Theory
Young and Helmholtz
three different retinal color receptors
red
green
blue

30. Color-Deficient Vision
People who suffer red-green blindness have trouble perceiving the number within the design

31. Visual Information Processing
Opponent-Process Theory- opposing retinal processes enable color vision
“ON” “OFF”
red green
green red
blue yellow
yellow blue
black white
white black

32. Opponent Process- Afterimage Effect

33. Visual Information Processing
Color Constancy
Perceiving familiar objects as having consistent color, even if changing illumination alters the wavelengths reflected by the object