Anticipatory shock task

 Before beginning the anticipatory anxiety task, each

 subject choose the intensity of shock. This was done by

 increasing voltage from 0 volts in five volt increments.

 Half second shocks were administered after each increase in

 voltage until the subject found the shock intensity

 "uncomfortable but not painful."

 Before the onset of the session, subjects were told

 which of two tones corresponded to shock trials and which

 corresponded to control trials. This two-stimulus paradigm

 is similar to that used by Vrana, et al. (1989) in which a

 warning signal is followed six seconds later by an electric

 shock. The subjects were instructed that during the shock

 trials at tone offset (after hearing the high tone), there

 will be a 6 second interstimulus interval which will be

 followed by a shock. In addition, the subjects were told

 that when they heard the low tone, it signaled that in six

 seconds, nothing would happen.

 Anticipatory reward task

 At the beginning of the sessions, subjects were told

which tone would indicate that they would receive a dollar

(or lottery ticket) and which tone was not associated with

reward. The higher tone always designated reward. The

designated tone for the reward trials was followed by a six-

second interval after which a message appeared on the

computer screen. The message read "You have won -- dollars"