Week 3 Flashcards
Signal detection theory
No fixed threshold. In conditions of uncertainty sensory/psychological factors determine people’s detection. Expectations and motivations play role. Hold stimulus intensity constant at slightly above threshold. Identifies detect ability and response bias
Hit
Signal plus noise
Miss
No on signal plus noise
False alarm
Yes on noise only
Correct rejections
No on noise only
Concept of distribution of neural activity
Amount never=0, varies all the time
Detect ability
How different is stimulus and the existence of already existing neural activity (sensitivity)
Decision rule(response bias)
Psychological input, motivational manipulations, amount of feeling
Discrimination
By how much must 2 stimuli differ before an observer reports a difference
Difference threshold experiment
2 stimuli presented and compared on each trial
Standard stimulus
Unchanging
Comparison stimulus
Varies systematically
Difference threshold
Person says greater than 75%
Point of subjective equality
Can’t tell difference,50%
Just noticeable difference
Smallest change from standard that can reliably be detected
Webers law
Size of JND in different experiments appears to be a constant fraction/percentage of the standard value
Scaling (magnitude estimation)
How much is there
Indirect scaling
Fechner. Start at threshold, find first JND, then combine 1st+2nd JNDs and so on. Assume webers law is true all JNDs are equal real amounts get bigger but same %
Fechners law
Initial changes in magnitude above threshold lead to more rapid changes in perceived intensity than subsequent changes
Direct scaling
Stevens approach. Directly map physical/psychological scales
Magnitude estimation procedure
Present standard to observer and assign a value. Series of trials present standard with 1 set of comparison stimuli. Ask subject to assign values in magnitude to standard. Plot data actual magnitude-estimated magnitude
Classical threshold theory
Ability to detect is limited by sensory threshold-minimal amount of energy required to activate receptors. Measured with constant stimulation either experiment or observer controlled. Can screen people for sensory/perceptual problems
