The influence of different doses of caffeine on visual task performance

Tn this study the influence of caffeine as an energy-increasing substance on visual information processing was examined. Subjects were presented with a dual-task consisting of two choice reaction time tasks. In addition, one of the tasks was presented at two levels of difficulty, influencing the decision-making process. Doses of 1.0, 3.0, and 7.5 mg/kg body weight caffeine and 3.0 mg/kg body weight lactose were administered (within-subjects design). The effect of caffeine was expected to be observable in terms of improved performance on measures like reaction time and type and number of errors, as well as in components of the event-related brain potential (ERP). The highest caffeine dose shortened reaction times on both the primary and the secondary task as compared to placebo. Overall there was a linear decline in reaction times on both tasks with increasing caffeine dose. As measured from ERP results, there was an increasing P3 amplitude as caffeine dose increased, indicating that the quantity of information processed was larger under caffeine. There was, however, no evidence of extra energy in terms of more hits and fewer misses or false alarms. Moreover, subjects reported no dose-related differences in amount of effort needed to perform the dual-task. It is concluded that the effect of caffeine, which is supposed to have its impact on both the input and the output stages of information processing, was evident in the output stage in the form of shortened reaction times. However, no effect of caffeine could be observed at the input stage, probably due to a data limited process.