Effect of Caffeine on Vigilance - II: Performance under High Demanding Condition Trayambak Tiwari*, Anju L. Singh** and Indramani L. Singh*** This experiment was conducted to examine whether the beneficial effect of caffeine is visible under a high demanding vigilance task. Thirty students (14 men and 16 women) aged 19 to 26 years (Mean age = 21 years) y participated in this experiment. They were required to detect a target over a non-target, across four 10-minute blocks in high 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 subjects factorial design was used. The task was designed on SuperLab ® 4.0 and displayed through a 15” colour monitor. Participants were instructed to press a designated key on response pad immediately after detecting a target and to ignore non-target. Correct detections (Hits), incorrect detections (False alarm) and reaction times were recorded as dependent measures. Sensitivity and response bias were calculated from the proportion of hits and false alarms. The results revealed that participants detected more targets and committed lesser false alarms under high intake (200 mg) of caffeine than low intake (100 mg) and placebo, thus suggesting 200 mg dose of caffeine as optimal dose for the best performance under high demanding vigilance task. Keywords: Caffeine, high demand, vigilance, sensitivity, response bias Indian Journal of Social Science Researches Vol. 7, No. 2, October 2010, pp. 29-37 ISSN 09749837 The growth of technology in the 20 th century has led to automation of tasks that have traditionally been the responsibility of the human operators. Tasks considered too dangerous, time consuming, or mundane for the humans are now performed by automated systems (i.e. military surveillance, industrial quality control, intensive- care monitoring, automotive cruise control; Warm, Dember, & Hancock, 1996). In turn, the responsibility of a human operator is now to monitor the tasks performed by the system. The human operator is required to maintain attention to the automated task, and it is essential that the operator notice any discrete change in the condition of the task. This means that the operator has to constantly monitor the task for a prolonged amount of time. The human operator has become the human observer. The ability to focus one’s attention and to maintain perceptual sensitivity to change in stimuli for a relatively long period of time is referred to as vigilance or sustained attention (Davies & Parasuraman, 1982; Warm 1984). However, it is somehow not possible for an operator to focus attention on one source of information for prolonged periods of time. Mackworth (1950) reported that detection efficiency of an individual deteriorated after first * Address correspondence to Dr. Trayambak Tiwari Assistant Professor, Cognitive Science Laboratory, Department of Psychology, Banaras Hindu University, Varanasi - 221005 (U.P.), India, e-mail: trayambakbhu@gmail.com ** Assistant Professor, Department of Psychology, Vasant Kanya Mahavidyalaya, Banaras Hindu University, Varanasi - 221010 (U.P.), India *** Professor,Cognitive Science Laboratory, Department of Psychology, Banaras Hindu University, Varanasi - 221005 (U.P.), India. Acknowledgement: We thank Prof. C. B. Dwivedi and two anonymous reviewers for their valuable feedback and comments. We also wish to thank Dr. Gaurav K. Rai and Anurag Upadhyay for their effective help in data collection in Cognitive Science Laboratory, BHU, Varanasi.