Performance is known to fall‐off with the time on a vigilance task. Treatment with methylphenidate attenuates this decrement while treatment with secobarbital enhances it. This experiment was designed to test whether this performance decrement and the drug effects on it are associated with changes in selective attention or in general state (i.e. motivation, alertness, or arousal). Subjects were treated with either 10 mg of methylphenidate, 100 mg of secobarbital, or a placebo in a double‐blind cross‐over design. Two event‐related potentials (N1 and P3) were measured to four tone pips presented in a random sequence. Only two of the four tones could occur in each ear. The task during the vigil was to detect a designated target tone pip. The amplitude of N1 was larger to both target and non‐target stimuli in the attended ear than to those in the unattended ear; P3 amplitude was larger only to the target stimuli. N1 amplitude decreased with time especially when secobarbital was administered. This decrement in N1 amplitude was comparable for both attended and unattended stimuli. The data support the view that the vigilance performance decrement and related drug effects on it are associated primarily with changes in general state.