Participants drank either regular root beer or sugar-free diet root beer before working on a probability-learning task in which they tried to predict which of two events would occur on each of 200 trials. One event (E1) randomly occurred on 140 trials, the other (E2) on 60. In each of the last two blocks of 50 trials, the regular group matched prediction and event frequencies. In contrast, the diet group predicted E1 more often in each of these blocks. After the task, participants were asked to write down rules they used for responding. Blind ratings of rule complexity were inversely related to E1 predictions in the final 50 trials. Participants also took longer to advance after incorrect predictions and before predicting E2, reflecting time for revising and consulting rules. These results support the hypothesis that an effortful controlled process of normative rule-generation produces matching in probability-learning experiments, and that this process is a function of glucose availability.

This study was designed to evaluate the effect of semantic priming with a lexical decision task in 22 depressed patients (DSM-III-R, 1987) and 30 control subjects. These patients were evaluated twice: first when they arrived at the hospital, and secondly, after clinical improvement. Clinical improvement was evaluated using standard depression rating scales. A lexical decision task involving semantic relations (related vs. unrelated, e.g., apple-pear) was used to evaluate the processing of semantic information. The results showed that, for the first evaluation, the depressives presented similar semantic priming to control subjects. When we compared semantic priming in the first and the second passes, we observed that its amplitude was identical. The sole difference between the two passes concerns the global reaction time in the depressive group. This last result suggested that, with clinical improvement, the characteristic psychomotor retardation declines. One of the major results concerns the fact that severe depressive patients (first pass) exhibit normal semantic priming in a lexical decision task. These results indicate, in this clinical population, the preservation of controlled processes implicated in this lexical decision task.