1. Introduction to Sensation and Perception
Module 11
Introduction to Sensation and Perception

2. Sensation
Sensation
the process by which our sensory receptors and nervous system receive and represent stimulus energy
Perception
the process of organizing and interpreting sensory information, enabling us to recognize meaningful objects and events

3. Sensation Sensation how do we change energy into sense Perception
what do we do with our sensory information

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

5. Sensation Bottom-Up Processing Top-Down Processing
analysis that begins with the sense receptors and works up to the brain’s integration of sensory information (piecing lines together to recognize the number 4)
Top-Down Processing
information processing guided by higher-level mental processes
as when we construct perceptions drawing on our experience and expectations (think you know someone and as they get closer, realize that you don’t)

6. Sensation- 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. Sensation- Thresholds
Absolute Threshold
minimum stimulation needed to detect a particular stimulus 50% of the time
isn’t constant – can change with motivation and alertness
Difference Threshold
minimum difference between two stimuli required for detection 50% of the time
just noticeable difference (JND)

8. Sensation- A. 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. Sensation- A. Thresholds
Signal Detection Theory
detection of stimuli involves decision processes as well as sensory processes
Example – riddle, shower/telephone

10. “You’re driving a bus with 12 passengers
“You’re driving a bus with 12 passengers. At your first stop, 6 passengers get off. At the second stop, 3 get off. At the third stop, 2 more get off, but 3 new people get on. What color are the driver’s eyes?
Did you detect the signal – who is the driver? – over the noise – number of passengers?

11. Sensation- A. Thresholds25 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

12. Sensation- A. Thresholds
Subliminal Messages
Reverse Speech - Voices From The Unconscious

13. Sensation- Thresholds
Difference Threshold
minimum difference between two stimuli required for detection 50% of the time
just noticeable difference (JND) – we experience the difference threshold as a JND.

14. Read the passage at the right.
How many lines do you require to experience a noticeable difference?

15. Sensation- D. Thresholds
Weber’s Law
to be perceived as different, two stimuli must differ by a constant minimum percentage (rather than a constant amount)
light intensity- 8% (1/60)
weight- 2% (1/50)
tone frequency- 0.3% (1/333)

16. Sensation- D. Thresholds
Sensory Adaptation
diminished sensitivity as a consequence of constant stimulation
(wearing a new wristwatch)
Selective Attention
focusing of conscious awareness on a particular stimulus
as in the cocktail party effect (listen to one voice, among many)

17. Now you see it, now you don’t!

18. Perception Selective Attention
Do you see circles with white lines or a cube?
Because attention is selective, you only see one interpretation at a time.

19. Change Blindness Change Blindness is an example of Selective Attention
Lab Demos

20. Change Blindness