Psychology 100:11
Chapter 5.1
Sensation
&
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.
Introduction
• My Psych 100 web site
– Power Point Lectures
– Syllabus
– Policies
– Lab information
– Interesting links
Psych 100 Page
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
Sensation
Vilayanur Ramachandran
From: A journey to the center of your mind
Sensation
• Three classes of interest
1. Physical stimuli
E.g, visible light, sound waves, odors, etc.
2. Physiological response
Electrical activity in sense organs, nerves, and
brain
3. Sensory experience
Psychological sensations
E.g., sound, sight, smell, taste, etc.
Sensation
Domains of questions
Physical
Stimulus
Sensory
Physiology
Psychophysics
Sensory
Experience
Physiological
Response
Sensory
Physiological
Psychology
Sensation
• Sensory coding
– Recording music
>Vinyl, tape, and digital codes
– Physical properties of stimuli -> neural code
> nerve impulses
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.
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.
Sensation
• Psychophysics
Gustav Fechner
– 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
Sensation
• The Weber fraction:
I = c
I
Ernst Weber
E.g, The Weber fraction for loudness c = 1/10
If 10 people hum, how many more must be added to notice
the difference?
I = 1
Answer: 1
10
10
If 50 people hum, how many more must be added
to notice the difference?
I = 1
Answer: 5
50
10
Sensation
• Other Weber Fractions:
– Vision:
– Kinesthesia:
– Pain:
– Pressure
– Smell
– Taste
1/60
1/50
1/30
1/7
1/4
1/3
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
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)
0
0
Conversation
1000 (103)
3
60
Bar band
100000 (105)
5
100
Jet airplane
10000000 (107)
7
140
- Loudest Band (130 - 140)?
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
Sensation
• Signal detection theory
- Payoff matrices
Stimulus
Response
Yes
No
On
Hit
Miss
Off
False
alarm
Correct
rejection
Sensation
• Signal detection theory
- Gullible student (Lax; yea-sayer)
Response
Test Item
True
False
True
90 %
10 %
False
60 %
40 %
Sensation
• Signal detection theory
- Skeptical student (strict; nea-sayer)
Response
Test Item
True
False
True
60 %
40 %
False
10 %
90 %
Sensation
• Signal detection theory
– Dissociates “Bias” from “Sensitivity
> Receiver operator charactistics
False Alarm Rate
.5
1.0
1.0
Lax
Hit Rate
Bias vs. Sensitivity
.5
Strict