Indian Journal of Social Science Researches Vol. 6, No. 2, Oct., 2009, pp. 8-16 ISSN : 0974-9837 Effect of Caffeine on Sensory Vigilance Task Performance-I: Under Low Demanding Condition Trayambak Tiwari*, Anju L. Singh** & Indramani L. Singh** The present experiment is designed to examine the effect of caffeine on sensory vigilance task performance. Thirty students of the Banaras Hindu University participated, whose mean age was 21.47 years. Participants were required to detect a target over a non-target, across four 10-minute blocks in low event rate condition. The ratio of target and non-target was 1: 4. A 3 (Treatment conditions: placebo, caffeine 100mg and 200mg) x 4 (10-minute blocks) within subject factorial design was used. Participants were instructed to press a designated key on response pad immediately after detecting a target and to ignore non-target. Correct detection (Hits), incorrect detection (False alarm) and reaction time were recorded as dependent measures. Signal detection theory (SDT) measures like sensitivity and response bias were also calculated from the proportion of hits and false alarms. The results of correct detection revealed that participants detected more targets under high intake of caffeine than low intake and placebo. The reaction time measure also revealed that participants took significantly more time to detect signal in placebo than caffeine intake conditions across blocks. In sum, the results suggest that 200mg dose of caffeine might be considered as the optimum dose for obtaining best performance in vigilance task scenarios. Key Words : Caffeine, Vigilance performance, Arousal, Decrement * Ph.D, Cognitive Science Laboratory, Department of Psychology, BHU, Varanasi-221005. Email : trayambakbhu@gmail.com ** Ph.D., Cognitive Science Laboratory, Department of Psychology, Banaras Hindu University, Varanasi-221005 (U.P.), INDIA. Email : anjubhu@rediffmail.com *** Professor, Cognitive Science Laboratory, Department of Psychology, Banaras Hindu University, Varanasi-221005 (U.P.), INDIA. Email: ilsingh_bhu@rediffmail.com Sustained attention may be defined as attention of prolonged periods of time. Today, sustained attention remains a relevant issue in a variety of occupations including industrial inspection, air traffic control and medical monitoring. However, it is somehow not possible for an operator to focus attention on one source of information for prolonged periods of time. Mackworth (1950), who was a pioneer researcher in this area, reported that detection efficiency of an individual deteriorated after first 15-20 minutes of work. This temporal decrement in the monitoring performance of vigilance task was called as vigilance decrement. The arousal and activation (Yerkes, & Dodson, 1908; Duffy, 1962; Malmo, 1959; Kahneman, 1973) theory of sustained attention suggested that the vigilance decrement could be a result of a progressive decline in cortical arousal which occurs due to the repetitive and monotonous nature of vigilance tasks. Moreover, Buck (1966) suggested that the vigilance decrement is determined by the relationship of the initial arousal level to some critical level below which performance degradation occurs. The critical level is set by target duration, difficulty, and other task (e.g., event rate) and individual factors (e.g., introversion-extraversion personality, temperament etc.). A decline in arousal (activation level) over time will result in an increase in reaction time (RT) but as long as arousal level exceeds the critical level, there is no decrement in detection accuracy. A decrement in both accuracy and speed occurs only when the critical level is high as in tasks with difficult targets. Caffeine in terms of cortical arousal has been shown to facilitate performance on vigilance tasks (Van der stelt & Snel, 1998). Lieberman (1992) suggested that the most reliable