Proposed mechanisms by which associative memory may enable preconditioned threat responses. Neutral events are shown in blue, affective events in orange. Dark colored events are directly perceived, and light colored events are mental. (A) Chaining: at the time of testing, PS presentation results in retrieval of the CS, which in turn activates the US representation, leading to pupil dilation. (B) Model-free integration: during conditioning, presentation of the CS results in retrieval of its associated PS, which integrates with the affective value of the US. At testing, the affectively charged PS triggers pupil dilation without the requirement of retrieving any associated stimuli. (C) Model-based integration: during conditioning, the PS is retrieved and forms a direct association with the US. At the time of testing, the PS leads to retrieval/prediction of the US, which in turn triggers pupil dilation.
