This procedure involves forcing the subject to choose from alternative choices, one of which contains the stimulus. A TWO-Alternative Forced Choice (2AFC) describes a subject choosing between two alternatives. Choosing from 4 alternatives is called 4AFC Choosing from 6 alternatives is called 6AFC
- 2AFC → 75% Threshold:
- As there is already a 50% chance of a correct response with 2AFC, threshold is commonly considered 75% seen level:
- As there is already a 50% chance of a correct response with 2AFC, threshold is commonly considered 75% seen level:
- 4AFC → 62.5% Threshold:
- For 4AFC seeing as the probability of error increases (only 25% of choosing the correct answer), the threshold is lowered to 62.5% (instead of 75% for 2AFC, or 50% for the yes-no procedure)
- 6AFC → 58,33%
- For 6AFC is at 58,33%