Figure 4

Experimental procedure. (a) Day 1: Fear acquisition. The CS + was followed in 75% of the time by an aversive picture, which served as US. The CS− was followed in 75% of the time by a neutral picture, which served as nUS. When not followed by a picture, CSs were fading into the grey background (1 s). Per trial a CS was presented for 7 s followed by a 1 s overlap of CS and US/nUS and then a 2 s only presentation of US/nUS. After each trial the ITI was presented (jittered between 4 and 6 s). Size of rings serving as CS + and CS− was counterbalanced. (b) Day 2: Generalization test. In addition to CS + and CS- serving as extremes, 8 rings of gradually increasing size were introduced as generalized stimuli (GS). After a 7 s presentation the CS or GS faded into the grey background. After each trial the ITI was presented (jittered between 4 and 6 s). (c) Group formation. The non-smoking group (group 1) did not smoke at all during the experiment. Group 2 (smokers) was asked not to smoke 1 h before and 6 h after the experiment on day 1. Group 3 (smokers) was asked not to smoke 1 h before the experiment and to smoke directly after the experiment on day 1. Group (smokers) 4 was asked to smoke directly before the experiment on day 1.