02-03. Scaling & signal detection

Question 1

Psychophysical scaling def?

Answer 1

describe relationships between subjective experience and stimulus intensity

Scale —> compare 2 things
—> subj. ex. & phys, intensity

3 laws!!

Question 2

What are the 3 laws called?

Answer 2

1. Weber’s Law
2. Fechner’s Law
3. Steven’s Power Law

Question 3

Weber’s Law? (explanation)

Answer 3

• JND gets bigger for increasing stimulus magnitudes
• (bigger stim. size = bigger JND)
• JND is CONSTANT proportion of intensity of standard
• fails at low intensities and near the threshold

Question 4

Weber’s law equation?

Answer 4

JND = k∗I
Weber fraction: k = JND/I

Question 5

Fechner’s law assumptions

Answer 5

1. Weber’s law is right
2. Each JND feels the same (the JND is the basic unit of perception)

• since Weber’s law fails, Fechner’s law does too

Question 6

Fechner’s law? (explanation)

Answer 6

• EQUAL increments in phys. int. produce SMALLER inc. in perceived magnitude
  –> adding a candle to a dark room vs adding a candle to a room with 100 candles
• PERCEIVED INTENSITY increases as a LOG function
• the change in physical intensity needed to produce one JND increases logarithmically as well (??)

Question 7

Fechner’s law equation?

Answer 7

S = k ln I/I₀

S=perceived intensity
k=weber fraction
ln = nat. log –> (IMPORTANT)
I=physical intensity
I₀=phys. int. @ threshold

graph is log (decreasing slope)

Question 8

Steven’s power law? (explanation) what sort of measurement does it use?

Answer 8

• says power function describes it better for more stimulus modalities
• uses magnitude estimation

Question 9

Magnitude estimation?

Answer 9

1. present standard stimulus with arbitrary number
2. present other stimuli and subject assigns number relative to standard

ex. standard line is 100, following lines are described as 200, 50, 75, etc

Question 10

Steven’s power law equation?

Answer 10

S = c * I^n

S=perceived
I=phys
c=constant
n=exponent

Question 11

Possible exponent values?

Answer 11

n > 1… perceived int. increases at INCREASING rate
- ex electric shock

n = 1… perceived int. increases at CONSTANT rate
- ex. line length

n < 1… perceived int. increases at DECREASING rate
- ex. brightness, auditory stim.
- (this does fit Fechner’s law)

Question 12

Signal detection theory? Experiment?

Answer 12

permits the measurement of a person’s sensitivity (to weak signal) while unaffected by their biases

Experiment:
- present weak stimulus with NOISE

Question 13

Signal detection experiment:

Answer 13

1. use 1 fairly WEAK stimulus
2. on every trial, present NOISE
3. Some trials have a signal embedded in the noise
4. Subject decides if they detect signal or not

Question 14

Possible responses for sig. detection

Answer 14

HIT (signal + yes)
FALSE ALARM (no sig + yes)
MISS (signal + no)
CORRECT REJECT (no sig + no)

You only need to know Hits and False Alarms to have all the information you need

Question 15

Receiver operating characteristic

Answer 15

graph where you can plot the proportion of hits and false alarms

shows all possible isometric curves

Question 16

Isometric curve (on ROC)

Answer 16

• Indicates an individual’s sensitivity by the curve that their data point (FAR, HR) falls on
• an individual can get 2 different data points ON THE SAME CURVE

top right corner is the most sensitive

diagonal line is random responses, completely insensitive

Question 17

Payoffs/bias affect isosensitivity curves?

Answer 17

• if you tell someone there’s gonna be a signal most of the time, they’re heavily biased to say yes (high false alarm rate)
• if there’s a big cost to missing (money, or in diagnosing diseases, etc), people are heavily biased to say yes as well
• payoffs/biases MOVE where a person’s dot is on the SAME isosensitivity curve!!

Question 18

Sensitivity def
True ___ rate?

Answer 18

True positive rate (Vertical axis)

How sensitive they are to detecting the signal

Question 19

Specificity def

Answer 19

True negative rate (horizontal axis)

How accurate they are in saying no when there isn’t a signal