Figure 1.

Standard signal-detection theory framework for interpreting responses in a two-alternative identification task. The two categories are represented by a and b, and the two possible behavioral responses by A and B. The discriminability of the two categories () is the number of standard deviations separating the distributions of the decision-variable values for the two categories. If the decision variable on a trial exceeds the decision criterion (), the response is B (the stimulus was from category b); otherwise the response is A.