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The present study examined the effects of sleep deprivation on performance, mood, and cardiovascular functioning in the late morning and early afternoon. The results showed that the sleep-deprived subjects felt less alert and detected fewer targets in a cognitive vigilance task. Selective impairments due to sleep deprivation were also observed in a logical reasoning task. There was little evidence to suggest that consumption of lunch altered these effects of sleep deprivation. However, individual differences in the effects of sleep deprivation were apparent, with trait anxiety being related to the changes in subjective alertness produced by sleep deprivation, and sleep-deprived extraverts showing greater performance impairments than the sleep-deprived introverts.

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.

This study examined the effects of fat content and meal size on postlunch changes in mood, performance, and cardiovascular function. Forty-six subjects (20 males, 26 females) were tested before and after lunch. Subjects were assigned to one of the following lunch condition: a) low fat (23 g), large meal (860 g); b) low fat (18 g), small meal (600 g); c) high fat (84 g), large meal (840 g); d) high fat (79 g), small meal (530 g). The results showed only small effects of fat composition and meal size, with no cardiovascular effects being observed and no evidence of fat content or the weight of the meal influencing performance of logical reasoning or cognitive vigilance tasks. A few effects of meal type were significant in the mood data, but given the large number of analyses conducted, these could represent chance effects. Results from two selective attention tasks showed that subjects given the high-fat meals responded more slowly but more accurately, which differs from the effects of carbohydrate, protein, and calorie content reported in earlier papers. Weight of the meal influenced the degree of distraction from near and far distractors and also the accuracy of responses to central and peripheral targets. However, both the effects of fat and meal size were modified by task parameters, and further research is required before firm conclusions can be drawn about the functional importance of the influences of nutrient content and meal size on performance. The high-fat and large meals were rated as more acceptable than the low-fat and small meals. These differences in acceptability could not, however, account for the changes in performance observed after consumption of the different meal types.

Two experiments examined the effect of breakfast (1.89 MJ) and caffeine (4 mg/kg) on cognitive performance, mood and cardiovascular functioning. In the first experiment, breakfast had no effect on performance of sustained attention tasks, but it increased pulse rate and influenced mood. The mood effects after breakfast differed between a cooked breakfast and a cereal/toast breakfast. In contrast to the effects of breakfast, this relatively high dose of caffeine improved performance of the sustained attention tasks, increased blood pressure and increased mental alertness. In the second experiment, effects of a breakfast and caffeine on mood and cardiovascular functions confirmed the results of the first study. The breakfast improved performance on free recall and recognition memory tasks, had no effect on a semantic memory task and impaired the accuracy of performing a logical reasoning task. In contrast to this, caffeine improved performance on the semantic memory, logical reasoning, free recall and recognition memory tasks. Overall, these results show that breakfast can improve performance in some but not all cognitive tasks and that these changes are very different from those observed after lunch, and those produced by caffeine.

An experiment was carried out to examine the effects of an evening meal and caffeine (3 mg/kg) on performance, mood and cardiovascular functioning. Subjects given a meal reported that they felt stronger, more proficient and more interested than subjects in the no-meal condition. They also performed a logical reasoning task more quickly than the no-meal group. However, no effects were found on sustained attention tasks or tasks involving recall or recognition of word lists. The effects of evening meals are, therefore, different from either those observed after lunch or breakfast. Caffeine improved alertness and performance on sustained attention tasks for the group as a whole. Interactions between caffeine conditions and levels of impulsivity of the subjects were also found in memory tasks.

The aim of the present study was to examine the effects of breakfast and caffeine on performance, mood and cardiovascular functioning in the late morning and after lunch. Forty-eight subjects were tested at 07.45 and subjects then assigned to one of the four conditions formed by combining caffeine and breakfast conditions. Subjects in the caffeine condition were given a dose of 4 mg/kg, the caffeine manipulation being double blind. At 11.15 subjects were given another coffee (subjects remained in the same caffeine condition) and had lunch at 12.30. Performance was examined prior to lunch (11.30) and after lunch (14.00). Effects of breakfast on recognition memory (lower false alarm rate) and logical reasoning (reduced accuracy) were found in the late morning but not after lunch. However, a semantic processing task was performed more slowly by the breakfast group after lunch. Caffeine improved performance on a sustained attention task, the logical reasoning task and semantic memory task. Subjects given caffeine also reported greater alertness and feelings of well-being, whereas the effects of breakfast on mood changed from the late morning to early afternoon. Few interactions between breakfast and caffeine conditions were obtained.