Abstract

EFFECTS OF CAFFEINE, BELIEFS ABOUT WHETHER CAFFEINE WAS CONSUMED, AND BELIEFS ABOUT THE BEHAVIOURAL EFFECTS OF CAFFEINE: A SECONDARY ANALYSIS OF SEMANTIC MEMORY AND CENTRAL EXECUTIVE TASKS

Dominic P. Nguyen-Van-Tam*, PhD and Andrew P. Smith, PhD

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Abstract

Background: There has been extensive research on the effects of caffeine on behaviour. Research has suggested that the effects of caffeine may vary depending on the ability to detect that caffeine has been administered and the expectancies about the effects of caffeine. These topics were examined here in analyses of semantic processing and logical reasoning (executive function) tasks. Methods: Secondary analyses of data from recently published studies are reported. One hundred and seventy-seven university students participated in the research. Baseline testing was carried out, and then separate groups either received a placebo or caffeine. The caffeine dose was 4mg/kg, and the manipulation was carried out double-blind. The dependent variables were the performance scores from semantic memory and logical reasoning tasks. Expectancies about the behavioural effects of caffeine and the ability to detect caffeine in a cup of coffee were measured by questionnaire. Results: The usual positive effects of acute caffeine were found for both the semantic processing and logical reasoning tasks. The ability to detect whether the coffee contained caffeine or not also had a significant effect. Expectancies about the effects of caffeine had no significant effect. There were no interactions between caffeine, correct detection of the caffeine and expectancies about the effects of caffeine. Conclusion: Acute effects of caffeine were observed for both tasks, confirming previous findings. Expectancies about the effects of caffeine had no significant effect. Those who could correctly detect whether the drink contained caffeine or placebo showed better performance, but this was an independent effect and did not modify the effects of the acute caffeine challenge.

Keywords: Caffeine; Discrimination; Expectancies; Memory; Semantic processing; Executive functioning; Logical reasoning.