An experiment was carried out to examine the effects of coffee on performance and alertness in the day and at night. The results showed that caffeinated coffee had a beneficial effect on alertness and improved performance on a variety of tasks in both day and night sessions. The effects were often very large. For example, at night, consumption of caffeinated coffee produced comparable alertness ratings to the day-time ratings given when juice was drunk. In contrast to the effects of caffeinated coffee, the difference between the decaffeinated coffee and juice were small and variable. Overall, these results clearly demonstrate the beneficial effects of consuming caffeinated coffee, and show that this effect is comparable in the day and night.
An experiment was carried out to determine whether a low dose of alcohol produced different behavioural effects in healthy volunteers to those suffering from an upper respiratory tract illness. Ninety-nine subjects were tested, with 48 subjects being assigned to the alcohol condition and 51 to the juice only condition. A dose of 1.5 ml of vodka per kg body weight was used and the alcohol manipulation was double-blind. Approximately half of the subjects in each condition were healthy and the others had upper respiratory tract illnesses, probably colds. Subjects with colds reported an increase in negative affect and were slower at performing psychomotor tasks. Few main effects of alcohol were obtained. Of major interest were the interactions between health status and alcohol conditions. The alcohol improved the mood of healthy subjects but produced greater negative moods in subjects with colds. Similarly, performance of selective and sustained attention tasks showed different effects of alcohol in healthy and ill subjects.
An experiment was carried out to examine the effects of caffeine and evening meals on sleep and performance, mood and cardiovascular functioning in the early morning of the next day. Forty-eight subjects were assigned to one of the four conditions formed by combining caffeine and meal conditions. Subjects in the caffeine condition were given 3 mg/kg caffeine in de-caffeinated coffee. The caffeine manipulation was double blind. Subjects in the meal condition were given a 3-course meal (∼ 1300 calories). Sleep was assessed by subjective ratings and these showed that both caffeine and consumption of the meal influenced sleep, but that there were no interactions between caffeine and meal conditions. Although caffeine disrupted sleep there was no evidence of performance or mood being impaired the next day. However, blood pressure was still higher the next day in subjects given caffeine the previous evening.
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