Instructed extinction after fear conditioning is relatively effective in attenuating electrodermal responding. Testing the single-process account of fear learning, we examined whether this manipulation similarly affects the startle response. Skin conductance responses (SCRs), startle responses, and online unconditioned stimulus (US) expectancy ratings were measured during fear acquisition (Day 1), extinction, and reinstatement (Day 2). Before extinction onset, half of the subjects were instructed that the conditioned stimulus would not be followed by the US (Instructed Extinction) whereas the other subjects were not instructed (Normal Extinction). This simple instruction completely abolished both differential SCR and US expectancy ratings, but not the startle fear response. Although the manipulation facilitated extinction
learning, it did not prevent the recovery of the startle response. The present findings are better explained by a dual- rather than a single-process account of fear learning.