Caffeine reaction-time tasks

There does, however, appear to be a ceiling on the acute dosage of caffeine that will enhance reaction time. At relatively low doses given prior to simple tasks or highly practiced complex tasks, the drug does enhance RT.41 104-117-143-144 However, these results may not apply to more complex tasks that have not been extensively practiced. For example, Lieberman79 found that 64 mg of caffeine decreased RT on a simple visual task in which the subject had to identify an object. However, the same dose of caffeine had no effect on RT when the subject had to choose objects in a more complex task. In fact, caffeine has been found to have detrimental effects on reaction times in some complex tasks.51 104 145 Again, there appears to be an inverted-U relationship between overall arousal — induced by the combination of caffeine and other arousal factors — and performance on reaction time tasks. 

Similar to caffeine, theophylline produces improvement on sustained attention tasks (Bryant et al. 1998), but caffeine appears to be a more potent CNS stimulant (Yu et al. 1991). Caffeine improves the accuracy of reaction time tasks in hyperkinetic children (Reichard and Elder 1977). 

The Walter Reed Army Institute of Research s Department of Behavioral Biology has developed a field-deployable version of a commercial Psychomotor Vigilance Task (PVT) that has been widely used in sleep research. The software runs on handheld PDAs running the Palm Operating System (Palm OS). It is modeled after the simple reaction time task of Wilkinson and Houghton,57 as modified by Dinges and Powell.58 The Palm OS version incorporates additional stimulus, feedback, control, and data options developed by Dr. Thome. In laboratory studies, performance on the PDA task has been shown to be sensitive to time-on-task fatigue effects, sleep deprivation, and circadian variation.18 Field studies have utilized the PVT to measure the efficacy of caffeine gum as a sleep loss countermeasure. 

A study in a large number of healthy subjects given a cup of coffee containing caffeine 300 mg/70 kg, either alone or immediately after drinking alcohol 0.75 g/kg, found that caffeine did not antagonise the deleterious effect of alcohol on the performance of psychomotor skill tests. Only reaction times were reversed. Two other studies also found that caffeine did not antagonise the effects of alcohol in a variety of tests. A further study in 8 subjects found that, contrary to expectations, caffeine increased the frequency of errors in the performance of a serial reaction time task, and similarly, caffeine has been reported to increase the detrimental effects of alcohol. ... 

Within minutes of consumption, a caffeinated beverage will cause the drinker to feel more alert. Simple intellectual tasks are performed more readily, as are physical jobs that require endurance. However, while reaction time is shortened by caffeine, fine motor control suffers, perhaps due to the slight tremor that becomes more pronounced with higher doses of caffeine. The larger doses of caffeine, especially for people who do not use it regularly, cause headache and nervousness. 

Although the effects of caffeine on some aspects of performance may be difficult to establish, the impact of this compound on tasks requiring vigilance or sustained attention is clearer. Lieberman et al. (110) evaluated the impact of 32-, 64-, 128-, and 256-mg doses of caffeine on a four-choice visual reaction time test (10 min), a continuous-performance task (variable duration), and the Wilkinson auditory vigilance test (1 hr). Results indicated that every dose of caffeine improved four-... 

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