Fig. 1.

Schematic diagram of the fear-potentiated startle experiment. Airblast were administered in 90-sec duration predictable (P) and the unpredictable (U) context but not during the 90-sec duration no-airblast (N) contexts. There were two 8-sec duration cues in each context (cues in N context are not shown in the graph). Airblasts were administered during a cue in the predictable condition and in the absence of cues in the unpredictable condition. A single airblast was delivered in each predictable and unpredictable context. Startle stimuli were delivered in the presence of each cue. Two startle stimuli were also delivered in the absence of cues (during intertrial intervals or ITI) in each 90-sec context. Potentiation of startle during a cue relative to during the absence of a cue was taken as the expression of cued fear. Potentiation of startle in the absence of the cue in the P and U condition relative to the N condition was taken as the expression of contextual anxiety. There were two sequences of stimuli, 1) PNUNUNP and 2) UNPNPNU. Subjects were presented with each of these sequences either with the sequence starting with P first or the sequence starting with U first.