1. Sensation & Perception
Psychology 100:11
Chapter 5.1
Sensation
&
Perception

2. Sensation and Perception
Outline
Introduction
Syllabus & code of conduct
Sensation and Perception
Phantom Limb Pain
Coding
Psychophysics
Study Question:
• What are four common elements of our various senses? Use examples from two senses to clarify your answer. 2

3. Introduction My Psych 100 web site Psych 100 Page Power Point Lectures
Syllabus
Policies
Lab information
Interesting links
Psych 100 Page

4. Sensation Sensation: The experience of a physical stimulus.
The initial steps taken by sense organs and neural pathways to organize information.
Perception: Subsequent organization and meaningful interpretation of physical stimuli.
Later processing steps that lead to internal representations of the stimulus
Ronald Melzack - The “King of Pain?”
“Pain is in the brain”
Ronald Melzack

5. Sensation Vilayanur Ramachandran
From: A journey to the center of your mind

6. Sensation Three classes of interest Physical stimuli
E.g, visible light, sound waves, odors, etc.
Physiological response
Electrical activity in sense organs, nerves, and brain
Sensory experience
Psychological sensations
E.g., sound, sight, smell, taste, etc.

7. Sensation Domains of questions Sensory Physiology Sensory
Physiological
Response
Physical
Stimulus
Sensory
Physiological
Psychology
Psychophysics
Sensory
Experience

8. Sensation Sensory coding Recording music
Vinyl, tape, and digital codes
Physical properties of stimuli -> neural code
nerve impulses

9. Sensation Common elements of the various senses
Receptors: Cells that respond to physical stimuli by creating electrical impulses.
Transduction: The process by which stimuli alter the balance of Na+ and K+ until a receptor reaches receptor potential.
Sensory Neurons: Neurons that carry the impulses from the receptor to the CNS.
Sensory Areas: Specific areas of the cerebral cortex designated for analyzing/organizing sensory information.

11. Sensation Quantitative and qualitative aspects
During transduction information concerning the quantitative and qualitative aspects of the stimulus are coded.
Quantitative information: The intensity of the stimulus, e.g., sound volume.
Coding quantity: Faster rate of responding
Qualitative information: Type of energy contained in the stimulus, e.g., sound frequency, colour.
Coding quality: Different receptors respond to different forms of energy.

12. Sensation Psychophysics
Gustav Fechner
Sensation
Psychophysics
Absolute Threshold: The critical level of intensity that gives rise to sensation.
Fechner and the difference threshold
Just Noticeable Difference (JND). The smallest difference between two similar stimuli that can be distinguished.
Weber: The size of a JND depends on stimulus intensity
e.g., 3 people hum + 1 more -> noticeable
100 people hum + 1 more -> not noticeable

13. Sensation The Weber fraction:
Ernst Weber
Sensation
The Weber fraction:
E.g, The Weber fraction for loudness c = 1/10
If 10 people hum, how many more must be added to notice the difference?
Answer: 1
If 50 people hum, how many more must be added to notice the difference?
Answer: 5

14. Sensation Other Weber Fractions: Vision: 1/60 Kinesthesia: 1/50
Pain: 1/30
Pressure 1/7
Smell 1/4
Taste 1/3

15. Sensation
Fechner’s law: Sensation strength grows as a function of the Log of stimulus intensity
E.g., 15 w, 30 w light bulbs vs. 30 w, 45 w
S = k log(I)
Where
S = magnitude of sensory experience
K = a constant
I = stimulus intensity
Gustav Fechner

16. Sensation Loudness is measured using this relationship:
S =decibels (dB)
I = sound pressure units
K = 20
Example     Sound pressure units (I)  Log(I)  20Log(I)= dB
Softest detectable 1 (100)
Conversation (103)
Bar band (105)
Jet airplane (107)
- Loudest Band ( )?

17. Sensation Signal detection theory
Human judgement and the absolute threshold
E.g., A radar operator during 9/11/01 versus a radar operator today
Sensation vs. decision
Discriminating a signal + noise from noise alone
Lax (yea-sayer) and strict (nea-sayer) criterion
E.g., Hits and false alarms on a true-false test

18. Sensation Signal detection theory - Payoff matrices Miss Hit Correct
rejection
False
alarm
Response
Yes No
Stimulus On
Off

19. Sensation Signal detection theory - Gullible student (Lax; yea-sayer)
10 %
90 %
40 %
60 %
Response
True
False
Test Item

20. Sensation Signal detection theory
- Skeptical student (strict; nea-sayer)
40 %
60 %
90 %
10 %
Response
True
False
Test Item

21. Sensation Signal detection theory Dissociates “Bias” from “Sensitivity
Receiver operator charactistics
Hit Rate
False Alarm Rate
1.0 .5
Strict
Lax
Bias vs. Sensitivity