The effects of acute exercise and caffeine on temporal generalization
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The primary purpose of this dissertation was to examine the effects of acute exercise on human information processing. A quantitative review of the literature on acute exercise and cognition demonstrated that information processing may be enhanced or impaired depending on when it is measured, the type of cognitive task used, and the type of exercise performed. During exercise, participants’ cognitive performance was impaired, ∆= -0.14, whereas following exercise there was a small improvement in cognitive task performance, ∆= 0.20. Speeded mental processes were facilitated both during and following exercise, and memory storage and retrieval were enhanced following exercise. Cycling was associated with enhanced performance during and after exercise, whereas treadmill running led to impaired performance during exercise and a small improvement in performance following exercise. The review also revealed that empirical studies on the effects of acute exercise on interval timing were needed. The ability to accurately time short intervals is critical aspect of cognitive performance. Thus, a second purpose of this dissertation was to examine the influence of acute exercise on interval timing. Due to the widespread use of caffeine as an ergogenic agent, the effects of caffeine and exercise were also explored. Exercise and caffeine were examined as arousal manipulations within the context of scalar expectancy theory, the leading contemporary theory of interval timing. Part of the success of this theory is the ability to predict how changes in arousal states influence timing behavior. If the basis of a duration judgment is timed under a normal state, then increasing the clock speed so that the current duration is timed with a faster clock will result in a behavioral shift relative to a condition where both durations are timed with the clock running at the same speed. It was hypothesized that acute exercise and caffeine would have effects on timing tasks similar to other manipulations that increase clock speed. As predicted, when a reference memory was timed under a normal state, exercise resulted in a behavioral shift that consistent with a faster internal clock. The results of the caffeine manipulation (5mg/kg) illustrated the sensitivity of the timing system. The basis of the timing judgments was generated following the administration of caffeine and placebo. For each group, the current durations were compared to a reference duration that had been timed with the clock running at the same speed, effectively washing out any differences in timing performance for the caffeine and placebo groups. Evidence that the basis of the judgments were timed with a faster clock in the caffeine condition was present in the task performed after rest. The generalization gradient for timing behavior that was measured after a decrease in arousal shifted to right, consistent with more “ticks” being associated with the standard due to a faster clock speed. More research is needed to isolate the effects of caffeine on the internal clock.