Orienting and alerting: effect of 24 h of prolonged wakefulness.

It is well known that a decrease in vigilance can easily occur during 24 h of continuous wakefulness, but no study has assessed whether and in what way extended wakefulness might affect spatial orienting. In other words, it is not clear what happens when a subject has to orient his attention during a state of poor vigilance, resulting from sleep loss or sustained wakefulness. The aim of this study was to investigate this issue. Twelve right-handed male subjects participated in the experiment, which took place on two consecutive days. On the first day, in order to evaluate baseline orienting attention, the subjects performed a covert orienting task (in which the cue stimuli generated endogenous shifts of attention), lasting 20 min; on the second day, during 24 h of prolonged wakefulness, the same task was performed 12 times, about every 120 min, beginning at 10.00 a.m. Results showed an overall slowing of reaction time across the sessions, indicating a linear decrease of vigilance. However, this vigilance decrease did not seem to affect attention-orienting mechanisms, suggesting that the two systems are independent of each other.