1. Sensation & Perception

2. Sensation & Perception
09/15/99
Sensation & Perception
Figure 3.Davis 2 from:
Kassin, S. (1998). Psychology, second edition. Upper Saddle River, NJ: Prentice Hall.
©1999 Prentice Hall 4

3. Some general terms Transduction Psychophysics
Sensation & Perception
09/15/99
Some general terms
Transduction
the conversion of physical stimulation into neural impulses
Psychophysics
the study of the relationship between physical stimulation and perceptual experience
©1999 Prentice Hall 6

4. Psychophysics Absolute Threshold:
Sensation & Perception
09/15/99
Psychophysics
Absolute Threshold:
the minimum stimulation needed to detect a stimulus.
©1999 Prentice Hall 6

5. Sensation & Perception
09/15/99
Absolute Thresholds
Vision: A single candle flame from 30 miles on a dark, clear night
Hearing: The tick of a watch from 20 feet in total quiet
Smell: 1 drop of perfume in a 6-room apartment
Touch: The wing of a bee on your cheek, dropped from 1 cm
Taste: 1 tsp. Sugar in 2 gal. water
From:
Davis, S., & Palladino, J. (1997). Discovering Psychology.
Upper Saddle River, NJ: Prentice Hall.
©1999 Prentice Hall 8

6. Psychophysics Difference Threshold (JND):
Sensation & Perception
09/15/99
Psychophysics
Difference Threshold (JND):
the minimum detectable difference between two stimuli
Weber’s law - two stimuli must differ by a constant percent of the standard stimulus to be perceived as “different.
Example: JND for weight = 2%, so ...
a 1 lb. weight has to be compared to a 1.02 lb. weight to be detected as different.
a 100 lb. weight has to be compared to a 102 lb. weight to be detected as different.
©1999 Prentice Hall 6

7. Vision

8. The Electromagnetic Spectrum
Sensation & Perception
09/15/99
The Electromagnetic Spectrum
Figure 3.3 from:
Kassin, S. (1998). Psychology, second edition. Upper Saddle River, NJ: Prentice Hall.
©1999 Prentice Hall 11

9. Sensation & Perception
09/15/99
Human Eye Structures
Figure 3.4 from:
Kassin, S. (1998). Psychology, second edition. Upper Saddle River, NJ: Prentice Hall.
Source:
©1999 Prentice Hall 12

10. Sensation & Perception
09/15/99
Trichromatic Theory
T. Young (1802) & H. von Helmholtz (1852) both proposed that the eye detects 3 primary colors
red, blue, & green
All other colors can be derived by combining these three
Problem: Afterimages
Figure 3.9 from:
Kassin, S. (1998). Psychology, second edition. Upper Saddle River, NJ: Prentice Hall.
©1999 Prentice Hall 16

11. Two stage process of color vision
Receptor level:
red, green or blue receptors
Ganglion and earlier processing level:
Opponent processing
red vs. green
blue vs. yellow
black vs. white

12. Visual Pathways Sensation & Perception 09/15/99 Figure 3.7 from:
Kassin, S. (1998). Psychology, second edition. Upper Saddle River, NJ: Prentice Hall.
©1999 Prentice Hall 14

13. Cortical Cells: Hubel & Wiesel
Sensation & Perception
09/15/99
Cortical Cells: Hubel & Wiesel
(videos)
Some cells in the visual cortex respond only to certain types of visual information
For example, a diagonal line moving up and down
These cells are called feature detectors
Figure 3.8 from:
Kassin, S. (1998). Psychology, second edition. Upper Saddle River, NJ: Prentice Hall.
Source:
Hubel, D. H.., & Wiesel, T.N. (196Davis 2). Receptive fields, binocular interaction and functional architecture in the cat’s visual cortex. Journal of Physiology, 160,
©1999 Prentice Hall 15

14. Perceptual Processing
Sensation & Perception
09/15/99
Perceptual Processing
Form Perception
How do we go from basic features to seeing people, dogs, etc.?
Grouping Principles
Proximity
Similarity
Continuity
Closure
Figure 3.23 from:
Kassin, S. (1998). Psychology, second edition. Upper Saddle River, NJ: Prentice Hall.
©1999 Prentice Hall 28

15. Depth Perception Seeing in 3-D space Take advantage of:
How do we do this when the retina is 2-D?
Take advantage of:
Binocular cues
Require both eyes
Monocular cues
Only requires one eye

16. Binocular Cues Retinal Disparity Convergence
The eyes receive slightly different views of the world.
Convergence
The eyes turn more toward the center as objects move closer.

17. Monocular Cues These include: Size (relative and familiar)
Interposition
Relative clarity
Texture gradient
Relative height
Relative motion
Linear perspective
Relative brightness

18. Relative and Familiar Size

19. Interposition

20. Relative Clarity

21. Texture Gradient

22. Relative Height

23. Relative Motion Far objects appear to move with you;
albeit at a slower rate.
Fixation
Point
Moving
Near objects appear
to move opposite of you.

24. Linear Perspective

25. Relative Brightness Brighter objects tend to be nearer.
This is also affected by the implied direction of illumination

26. Is Depth Perception Innate?
Sensation & Perception
09/15/99
Is Depth Perception Innate?
The Visual Cliff
Devised by Eleanor Gibson and Richard Walk to test depth perception
Glass surface, with checkerboard underneath
Babies go to Mom on “shallow” size
Figure 3.27 from:
Kassin, S. (1998). Psychology, second edition. Upper Saddle River, NJ: Prentice Hall.
(video)
©1999 Prentice Hall 31

27. Cultural Effects - An Example
Sensation & Perception
09/15/99
Cultural Effects - An Example
The Ames Room
A specially-built room that makes people seem to change size as they move around in it
The room is not a rectangle, as viewers assume it is
A single peephole prevents using binocular depth cues
Figure 3.24 from:
Kassin, S. (1998). Psychology, second edition. Upper Saddle River, NJ: Prentice Hall.
(video)
©1999 Prentice Hall 29

28. Hearing

29. What is the stimulus? Particle movement
can be air, water, bone, etc.
This movement can be described as a wave form
amplitude
wavelength (frequency)

30. The Human Ear Sensation & Perception 09/15/99 Figure 3.13 from:
Kassin, S. (1998). Psychology, second edition. Upper Saddle River, NJ: Prentice Hall.
©1999 Prentice Hall 21

31. How do we … ? Encode Loudness Encode Pitch
encoded by the number of neurons firing
Encode Pitch
Place theory vs. Frequency theory

32. How do we determine pitch?
Place Theory
Pitch is encoded by where the sound wave triggers waves on the basilar membrane.
Beginning;
near oval
window
End;
near round
window
High
Freq.
Low
Freq.
Basilar Membrane

33. How do we determine pitch?
Frequency Theory
Neurons fire at same rate as the frequency of the sound.
ex. if a sound wave has 100 pressure peaks per second (100 Hz), then the neural signals will fire 100 times per second.

34. How do we hear pitch? High Frequencies Low Frequencies Everything else
Place Theory
Low Frequencies
Frequency Theory
Everything else
some combination of the two

35. Auditory Localization
Sensation & Perception
09/15/99
Auditory Localization
Sounds from different directions are not identical as they arrive at left and right ears
Intensity
Timing
The brain calculates a sound’s location by using these differences
Figure 3.14 from:
Kassin, S. (1998). Psychology, second edition. Upper Saddle River, NJ: Prentice Hall.
©1999 Prentice Hall 22