Signal Detection Theory (advanced)

Question 1

Two-alternative forced choice (2-AFC) sens

Answer 1

d’= 1/√2 [z(H)-z(F)]

Question 2

Two-alternative forced choice (2-AFC) respons bias

Answer 2

Methods to calculate response bias are exactly the same as discussed earlier.

In a 2-AFC task, observers do not regularly display extreme biases (compared
to yes/no experiments). Because of this p(c) is sometimes argued to be a good
sensitivity measure in this context

2-AFC area theorem: p(c) in 2-AFC by an unbiased observer equals the area
under the yes-no isosensitivity curv

Question 3

Two-alternative forced choice: √2 Relationship

Answer 3

Not always observed

Question 4

Two reasons why 2AFC tasks have been adopted a lot:

Answer 4

• It discourages response bias

- Performance levels are high, and thus smaller stimulus differences can be measured

Question 5

SDT and time

Answer 5

See ppt

Question 6

Sequential analysis (SA) has inspired much research

Answer 6

It can explain the tradeoff between speed and accuracy

It allows to dissociate between evidence (which is stationary) and the DV (which evolves in time), which is not possible in SDT frameworks.

it fits empirical data well, and has inspired researchers to look for neural correlates of
evidence accumulation

Question 7

SDT and clinical diagnosis

Answer 7

• The power of this approach depends on the prevalence (i.e. the base rate) of
  the variable considered (below, a 9:1 ratio).

- For a fixed cut-point (say, point B), the sensitivity and specificity indices will
not change (i.e. the proportion of de- pressed persons classified as depressed
will remain constant), but the practical utility of the measure will change as a
result of changes in the base rate.

Question 8

SDT and Baseyian inference

Answer 8

P(A|B)= P(B|A)*P(A) / P(B)

People are unfimiliar with probabilities, reason in frequencies