Human evaluative conditioning: order of stimulus presentation

In an experiment designed to demonstrate evaluative conditioning, subjects were shown 48 pictures of sculptures that they rated on a scale with 21 categories (-10 to +10). Then, the two most liked pictures (L) were paired with pictures from the categories -1, 0, or +1 (N). In contrast to prior experiments, subjects were given either forward conditioning (N-L) or backward conditioning (L-N) trials but not both. Four other neutral stimuli were paired with each other (N-N) and acted as control stimulus pairs. After conditioning, the stimuli were rated a second time. There was a statistically significant difference in evaluative ratings showing a change of the evaluative tone of the previously neutral stimuli in a positive direction only after forward conditioning. This finding is inconsistent with results of prior experiments and challenges the assumption of Martin and Levey (1987) that evaluative conditioning is different from human classical conditioning.