Electronic Theses and Dissertations

Date of Award


Document Type


Degree Name

Ph.D. in Psychology



First Advisor

Dr. Karen A. Christoff

Second Advisor

Dr. Thomas W. Lombardo

Third Advisor

Dr. Stanley P. Brown

Fourth Advisor

Dr. Nathan C. Weed


University of Mississippi

Relational Format



Research findings on the effects of caffeine on mood have been mixed. Some studies report that caffeine increases anxiety and alertness while others do not. The variability in outcome of caffeine studies may be due to the insensitivity of self-report measures. An alternative to self-report is facial EMG which may be superior to self-report since the degree of concordance between facial EMG and affective valence ratings is considerably higher than the degree of concordance between behavioral, self-report, and physiological measures. Typically, studies investigating the effects of caffeine on mood have tested caffeine's effects on idiosyncratic mood states which prevailed in the laboratory at the time of testing. No studies however, attempted to manipulate a subject's mood state at the time of testing. Conflicting results observed across these studies may have been due to the degree of anxiety that individual laboratories or protocols elicited at the time of testing. This study manipulated affect and examined the effects of caffeine on positive, negative, and neutral affect. Affective changes were assessed with self-report and facial EMG measures.

A two factor repeated measures design, drug dose by type of affective imagery, was executed with three dependent measures. Three drug doses, 0, 4.0, and 8.0 mg/kg of caffeine citrate, were orally administered double blind through solution in fruit juice to each of 20 female subjects on three separate occasions. Following drug, facial EMG was recorded at the corrugator and zygomatic sites while subjects engaged in multiple imagery trials. At post-trial, subjects rated each formed image for happiness or anger on a scale of 0 to 100. After the last session, subjects rated their expectancy of caffeine's effects on mood, and attempted to identify sessions in which caffeine was administered. The mood manipulations were successful based on results from self-report data, but not EMG data. Neither self-report nor EMG measures showed effects of caffeine on mood. The fact that subjects were generally unable to discriminate when they received caffeine is consistent with finding no mood effects based on recent research relating caffeine discriminability and mood effects. Reasons for the absence of drug effects are discussed.

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