to Approaches studying perception 1. Physiological: the relationship between
the physical stimulus and responses in the nervous system or the responses in the nervous system and perception
Learn about receptors, neurons, and neural pathways.
Approaches to studying perception (continued)
2. Phenomenological descriptions of, or musings upon, experiences
Disadvantages: can't observe non-conscious processes observations are colored by expectations & knowledgea handle on why experiences occur can't get
Approaches to studying perception (continued)
3. Psychophysical: Investigations of the relationship between the PSYCHOlogical response and
the PHYSical stimulus.
(Fechner, 1860)
Psychophysics can be used to find limits of sensory systems. Example 1: Thresholds What is the smallest amount of physical stimulation necessary for detection? Classical Psychophysical Methods
1. Method of adjustment (TV whine)
2. Method of Limits
Crossover Points (Mean = Threshold)
Willingness to say "yes"
3. Method of constant stimuli
Multiple light intensities, many samples of each , randomly intermixed Percentage of Trials on which each intensity is detected
3. Method of constant stimuli (continued)
Function one might expect "step function"
Multiple light intensities, many samples of each , randomly intermixed Percentage of Trials on which each intensity is detected
3. Method of constant stimuli (continued)
Function typically obtained "ogive"
"Absolute" threshold
"Absolute" threshold tells you about the sensitivity of the system. Defined statistically: 50% "yes, I detect it" responses
threshold = limen (latin) below threshold = subliminal above threshold = supraliminal
Buzz Group
Is it true that a below-threshold (subliminal) stimulus is perceived?
What never does that imply about subliminal advertising? Elaborate! SUPPORT YOUR ANSWERS!
TIP: Buzz group topics are potential essay question topics
Psychophysics can be used to find limits of sensory systems.
Example 1: Absolute thresholds
Example 2: Difference thresholds The smallest difference between two stimuli
that a person can detect
AKA:
Difference limen (DL) Just noticeable difference (JND)
JND changes with the magnitude of the stimuli
Examples
Difference threshold for a particular attribute
Applying Weber's Law:
Suppose JND for 10 candles is 1 candle
Weber fraction = 1/10 = 10%
JND for 100 candles candles 1500 60 candles
10 150 6
Psychophysics can also be used to examine perception above threshold.
Suprathreshold perception
To determine when a subject's perception of intensity is 2X 4X 10X as large as another.
Method: Magnitude Estimations S. S. Stevens
standard (aka "modulus")
assign a number to perceived intensity
comparison stimuli
assign number relative to the standard
Line length
units on graph paper
Perceived Length (if 1:1) "100"
Standard/Modulus 200
1
2 3 4 5 6 7 8 9 10
40
325 485 100 200 400 580 65 145 260
"20"
"162.5" "242.5" "50" "100" "200" "290" "32.5" "72.5" "130"
Relationship between physical stimulus and psychological response is not always 1:1
Response compression: Response magnitude grows more slowly than stimulus magnitude (e.g., brightness)
Response expansion: Response magnitude grows more quickly than stimulus magnitude (e.g., pain)
Stevens' Power Law P = KSn P = perception K = constant S = stimulus n = exponent (power)
Exponent of power function for area = 0.70 Response compression?
Response expansion?