Detecting contrasts

Question 1

What is 4 AFC test?

Answer 1

• stare at the computer
• you have four beeps
• have to decide which beep has the faint visual stimulus
• 4 choices still have to choose 1

Question 2

How would you get wrong answer?

Answer 2

• if stimulus is faint or eyes are closed chance of response = 1/4
• if stimulus is really bright response would have accuracy of 100%

Question 3

How can observer make errors?

Answer 3

Hallucinations

dont see anything and guess answer

Question 4

Why are two frequency of correct responses used ?

Answer 4

One frequency measures the first correct response 1/4

one frequency measures the second correct response which can be a guess and is reduced to 1/3

Question 5

What is better predicting guessing theory or second response correct

Answer 5

Theory shows that there is higher success rate for second response than by predicting by guessing theory

Question 6

What did swets et al theopry suggest?

Answer 6

Swets et al suggested that all forced choice test errors are caused by hallucinations and SDT quantifies this

Question 7

What does SDT stand for ?

Answer 7

Signal- detection theory?

Question 8

Who came up with SDT and when?

Answer 8

Swets et al in 1961

Question 9

What are the units of sensation intensity?

Answer 9

we dont know

Question 10

What is univariance?

Answer 10

All responses in a detection experiment are based on perceived intensities along a single sensory dimensions

Question 11

How are normal intensity determined in SDT?

Answer 11

Sigma - Determines the normal density width

Mu- determines the density position on H axis

Question 12

What does σn stand for?

Answer 12

Standard deviation of non target distribution

Question 13

What is similar in SDT?

Answer 13

Same SD and variance

Question 14

What could real targets produce?

Answer 14

More varied sensation than non targets

Question 15

what happens when variance is 0 ?

Answer 15

There is no increase

Question 16

What happens when variance increases?

Answer 16

Variance increases density of S gets flatter

Question 17

What happens to second response and variance increases?

Answer 17

Variance increases , density of S gets flatter and second response accuracy decreases?

Question 18

When was the good fit found in SDT?

Answer 18

Between 0.2 and .03

Question 19

What is intrinsic uncertainty?

Answer 19

Maximum activity in several independent sensory mechanisms, only one of which is actually sensitive to stimulus

Question 20

What happens when uncertainty increases?

Answer 20

Second response accuracy falls

Question 21

How many independent mechanisms are used in decision process?

Answer 21

When one use no uncertainty

Question 22

What happens when sensory threshold increases?

Answer 22

More and more of density functions are collected at 0 and once second response accuracy falls

Question 23

What does increasing variance and intrinsic uncertainty do?

Answer 23

Produce similar predictions

Question 24

What were the three explantation from Swets et al?

Answer 24

Increasing volume
intrinsic uncertainty
a sensory threshold

Question 25

What do error bars contain?

Answer 25

95% confidence intervals

Question 26

What changed the confidence intervals?

Answer 26

Number of trials

Question 27

What do more trials do?

Answer 27

Increase in number of trials gives smaller confidence intervals and determines accuracy

Question 28

If threshold is plotted against pedestal intensities what happens?

Answer 28

curve shape called dipper

Question 29

What does sensory noise do with average sensation?

Answer 29

Sensory noise does increase with the average sensation

Question 30

What are two ways that observer makes errors ?

Answer 30

Hallucinations

Sensory threshold