Figure 1

Experimental Design. (a) Working memory paradigm (schematic, in reality gratings were Gabors and background was gray). Trials started with 500 ms of fixation, followed by a Sample phase (3,000 ms in Experiments 1, 2, and 3; 300 ms in Experiments 4 and 5) in which three oriented Gabor patches were displayed (drawn here schematically as square wave gratings), surrounded by colored rings that were used as reward prediction cues in Experiments 1, 2, and 5. Participants remembered the orientations of the Gabors during a 2,000 ms memory maintenance phase and adjusted the orientation of a randomly selected target to match the memorized orientation in the Response phase. Feedback was provided about performance on each trial. (b) In Experiments 1, 2, and 5, the color of the rings around the targets was associated with a specific reward level (valid predictors in Experiments 1 and 5; no predictive value in Experiment 2). The participants first learned the association between color and reward level in a separate color-reward association task (right panel) in which they reported the color of three visual targets as quickly as possible. Feedback was provided about performance after every trial. (c) In Experiments 3 and 4, the contrast of the Gabors was manipulated to modulate the targets’ salience. In Experiments 3 and 4A the three targets differed in contrasts. In Experiment 4B all targets had the same contrast but the contrast level was varied across trials. (d) An overview of the different Experiments and their crucial parameters. Differences among experiments concern the duration of the sample phase, the presence and relevance of colored rings, and the presence and type of contrast manipulations.