1. Sensation and Perception
Sensation & Perception
4/21/2017
Sensation and Perception
Prepared by Krista D. Forrest, Ph.D., and Michael Lee
These slides © 2004 Pearson Education Canada Inc., Toronto, Ontario.
Chapters 5 and 6
©1999 Prentice Hall

2. Defining Sensation and Perception
Sensation & Perception
4/21/2017
Defining Sensation and Perception
Sensation
The detection of physical energy from our environment which we encode as neural signals.
It occurs when energy in the external environment or the body stimulates receptors in the sense organs.
“Taking it all in.”
Perception
The process by which the brain selects, organizes and interprets our sensory sensations.
Making sense of what we have taken in.
©1999 Prentice Hall

3. Sensation & Perception
4/21/2017
Separate Sensations
Sense receptors: Specialized cells that convert physical energy in the environment or the body to electrical energy that can be transmitted as nerve impulses to the brain.
Where are some of your sense receptor cells?
Sensory Transduction: process by which our sensory systems convert stimulus energy into neural messages.
That the brain will understand.
©1999 Prentice Hall

4. Sensation & Perception Processes
4/21/2017
Sensation & Perception Processes
Figure 3.Davis 2 from:
Kassin, S. (1998). Psychology, second edition. Upper Saddle River, NJ: Prentice Hall.
©1999 Prentice Hall

5. Sensation & Perception
4/21/2017
Bottom-up Processing
Sensory analysis that starts at the entry level.
Begins with the sensory receptors
Moves up to the brain.
©1999 Prentice Hall

6. Sensation & Perception
4/21/2017
Top-down Processing
How our minds interpret what our senses detect.
The experiences and expectations we use to interpret information.
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©1999 Prentice Hall

7. Sensation & Perception
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The Forest Has Eyes
©1999 Prentice Hall

8. Sensation & Perception
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The Forest has Eyes
Bottom-up: Our sensory systems detect the lines, angles and colors that form the horses, rider and surroundings.
Top-down: We consider the title, notice the apprehensive expressions, then direct our attention to the parts of the painting that give those observations meaning.
©1999 Prentice Hall

9. Sensation & Perception
4/21/2017
Ambiguous Figure
What do you sense?
Bottom-up
What do you perceive?
Top-down
©1999 Prentice Hall

10. Sensation & Perception
4/21/2017
©1999 Prentice Hall

11. Sensation & Perception
4/21/2017
What did she say?
“Mares eat oats and does eat oats. And little lambs eat ivy. A kid’ll eat ivy, too. Wouldn’t you?”
©1999 Prentice Hall

12. Sensation & Perception
4/21/2017
Absolute Threshold
The smallest quantity of physical energy that can be reliably detected by an observer.
The stimulation needed for us to detect the stimulus 50% of the time.
We are more sensitive to some things than others.
©1999 Prentice Hall

13. Absolute Sensory Thresholds
Sensation & Perception
4/21/2017
Absolute Sensory 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
©1999 Prentice Hall

14. Signal Detection Theory
Sensation & Perception
4/21/2017
Signal Detection Theory
Predicts how and when we will detect a faint stimulus (signal) amid background stimulation (noise).
Assumes detection depends partly on a person’s experiences, motivation, and level of fatigue.
Absolute thresholds vary.
Seeks to understand why.
©1999 Prentice Hall

15. Sensation & Perception
4/21/2017
Subliminal Stimuli
Stimuli that is below our absolute threshold.
We can process information without being aware of it.
May have a subtle, fleeting effect on thinking.
©1999 Prentice Hall

16. Sensation & Perception
4/21/2017
The Pepsi Cool Can
In 1990, Pepsi withdrew one of its
“Cool Can” designs after
someone protested that Pepsi was
subliminally manipulating people by designing the cans such that when six packs were stacked at grocery stores, the word SEX would emerge from the seemingly random design.
Critics alleged that the red and blue lines on the “Cool Can” design were far from random.
©1999 Prentice Hall

17. Sensation & Perception
4/21/2017
Backmasking
Backmasking site
Listen to the song. Can you tell what it says?
What type of processing is this?
©1999 Prentice Hall

18. Signal Detection Theory
Sensation & Perception
4/21/2017
Signal Detection Theory
Tries to understand why people respond differently to different stimuli.
Absolute thresholds vary.
Our psychological and physical states influences our ability to detect stimulus.
©1999 Prentice Hall

19. Sensation & Perception
4/21/2017
Difference Threshold
The smallest difference in stimulation that can be reliably detected by an observer when two stimuli are compared;
Also called Just Noticeable Difference (JND).
It increases with the magnitude of the stimulus.
Weber’s Law: The size of the JND is proportional to the intensity of the stimulus.
©1999 Prentice Hall

20. Sensation & Perception
4/21/2017
Sensory Adaptation
The reduction or disappearance of sensory responsiveness when stimulation is unchanging or repetitious.
Jumping in a swimming pool
After constant exposure to stimulus our nerve cells fire less frequently.
Habituation
Prevents us from having to continuously respond to unimportant information.
©1999 Prentice Hall

21. Sensation & Perception
4/21/2017
Sensory Overload
Over-stimulation of the senses.
Can use selective attention to reduce sensory overload.
Selective attention
The focusing of attention on selected aspects of the environment and the blocking out of others.
©1999 Prentice Hall

22. Sensation & Perception
4/21/2017
Vision: What We See
What strikes our eyes is not color but pulses of electromagnetic energy that our visual system experiences as color.
Different species see different portions of the spectrum.
©1999 Prentice Hall

23. Sensation & Perception
4/21/2017
Waves
Wavelength: The distance from one peak to the next.
Determines the color we experience or hue.
Short wavelengths also mean higher pitched sounds.
©1999 Prentice Hall

24. Sensation & Perception
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Waves
Intensity: The height of the light waves. Determines the brightness.
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)
©1999 Prentice Hall

25. Sensation & Perception
4/21/2017
An Eye on the World
Cornea
Protects eye and bends light toward lens.
Lens
Focuses on objects by changing shape.
Iris
Controls amount of light that gets into eye.
Pupil
Widens or dilates to let in more light.
©1999 Prentice Hall

26. Sensation & Perception
4/21/2017
An Eye on the World
Retina
Neural tissue lining the back of the eyeball’s interior, which contains the receptors for vision.
Made from a piece of brain as fetus
Rods
Visual receptors that respond to dim light.
Share bipolar cells with many other rods.
Cones
Visual receptors involved in color vision. Most humans have 3 types of cones.
Help detect fine details
Located in fovea
Have a “hotline to the brain” with own bipolar cells.
©1999 Prentice Hall

27. The Structures of the Retina
Sensation & Perception
4/21/2017
The Structures of the Retina
©1999 Prentice Hall

28. Sensation & Perception
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The Optic Nerve
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.
©1999 Prentice Hall

29. Sensation & Perception
4/21/2017
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
©1999 Prentice Hall

30. Visual Information Processing
Sensation & Perception
4/21/2017
Visual Information Processing
Feature Detectors
Nerve cells in the brain that respond to specific features of the stimulus
shape
angle
movement
Stimulus
Cell’s
responses
©1999 Prentice Hall

31. Sensation & Perception
4/21/2017
Parallel Processing
Parallel Processing
processing several aspects of a problem simultaneously
The retina projects to several areas of the visual cortex at the same time.
Blindsight
the brain’s natural mode of information processing for many functions, including vision
©1999 Prentice Hall

32. Sensation & Perception
4/21/2017
Trichromatic Theory
Young (1802) & von Helmholtz (1852) both proposed that the eye detects 3 primary colors:
Red, blue, & green
Three different types of cones, one for each color.
All other colors can be derived by combining these three.
Figure 3.9 from:
Kassin, S. (2001). Psychology, third edition. Upper Saddle River, NJ: Prentice Hall.
©1999 Prentice Hall

33. Opponent-Process Theory
Sensation & Perception
4/21/2017
Opponent-Process Theory
A competing theory of color vision, which assumes that the visual system treats pairs of colors as opposing or antagonistic.
If you see one color on one point of the retina you can’t see the other at the same time.
Red and green
Blue and yellow
Black and white
©1999 Prentice Hall