It is easier to introduce the model with an example, so suppose that we have
designed a face memory experiment. In the first part of the experiment, a
participant was asked to memorize a list of faces. Then the participant is
presented with a set of faces one at a time. Some of these faces were seen
before (these are old faces) and some were not seen before (these are new
faces). The task is to decide for each face if this face was seen (response Yes)
or not (response No) in the first part of the experiment.