Can being told you drank caffeine change your attention or memory test performance?

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The researchers separated what participants actually drank from what they were told about it. Each participant attended four sessions, trying each combination of coffee and message. Participants were also grouped by whether they had reported expecting caffeine to stimulate them before the experiment.

No effects of the message were found on the attention or memory tasks. Actual caffeine had more selective effects: it improved performance on a task involving detecting signals compared with decaffeinated coffee among participants who expected stimulation, but not among those who did not. However, the message did not give the group expecting stimulation a greater advantage than the other group.

On a task that involved searching memory, responses were faster with caffeine, but correct detections and false alarms showed no clear differences between drinks or expectation groups. Neither caffeine nor the message affected later recall performance. Overall, the results only partly supported the researchers’ hypothesis that caffeine and messages would affect the expectation groups differently. Because expectations were reported rather than experimentally assigned, the group differences do not show that expecting stimulation caused caffeine to work better.