Appendix: Noise and Signal Detection Theory

Question 1

Noise

Answer 1

random variation in number of action potentials produced by neurons in response to fixed sensory stimulus

Question 2

What can psychophysics be used for?

Answer 2

• Sensory system neurophysiology/ neuropsychology
  - Sensory limits of vision, hearing, touch…
  - Interspecies comparison
  - Inferring neuronal mechanisms
• Experimental psychology
  - Visuomotor interactions
  - Perception of speed, motion
  - Attention
• Quantitative measurement of perceptual states
  - Diagnostic tool
  - Assessment tool

Question 3

Decision Criterion

Answer 3

threshold used when deciding whether stimulus was presented or not

Question 4

Psychometric Function

Answer 4

plot of proportion of stimuli detected or discriminated vs stimulus intensity

• Ideal psychometric function: step function (fixed threshold)
• Real psychometric function: S- shaped (sigmoid or logistic) function

Question 5

Method of Limits

Answer 5

either ascending or descending direction

• doesn’t change direction when stimulus is detected
• continue in many trials but vary the starting point
• similar to method of adjustment

Question 6

Effect of noise on psychometric function

Answer 6

Detection or discrimination of stimulus is always subject to noise:

• Neural
• Stimulus (physical)
• Participant Distraction:
  - Attention
  - (Response)

Question 7

Signal Detection Theory

Answer 7

framework for measuring how many people make decisions in presence of noisy perceptual evidence
- disregards decision- making style

• how stimuli are detected/ discriminated against background noise
• how to make decisions in the presence of uncertainty
• how to make optimal decisions from ambiguous data
• how to make good decisions from bad information
• allows measurement of sensitivity

Question 8

SDT Outcome

Answer 8

SIGNAL. DECISION. CONSEQUENCE
yes. yes hit
yes no. miss
no. yes. false alarm
no. no. correct rejection

Question 9

Receiver Operating Characteristics

Answer 9

quality of participants performance (hit/ false alarm)

Question 10

Decision- Making Bias

Answer 10

participant’s tendency to be liberal or conservative when deciding if stimulus is present

Question 11

Low Criterion

Answer 11

• decision for any kind of noise

- alert for every blob: make sure you never miss- but many false alarms

Question 12

High Criterion

Answer 12

• make very strict decision for what to respond to

- only alert for really big blobs: no false alarms- but many misses

Question 13

Utility

Answer 13

satisfaction from results of decision

Question 14

Discriminatory d’

Answer 14

distance between means of noise curve and stimulus+noise curve

Difference between the hit rate and false alarm rate

High d’- very little overlap between options
Low d’- lots of overlap
- low sensitivity
- more misses and false alarms