Event-related potentials (ERPs) were recorded to square-pattern stimuli presented either to the upper or the lower half of the visual field. in the Same task the subjects had to respond to the fifth stimulus of a microsequence of stimuli that appeared on the same half field, whereas in the Different task the target stimulus was the alternation of stimulus location after a microsequence of four stimuli to the same half field. The pattern-specific CII component (a negative wave to lower half-field stimulation with 100 ms latency) appeared to be insensitive to task variables. N1 increased to the uncertain alternations of stimulus location. An N2 component with temporal maximum emerged to Nogo stimuli (to the fifth stimulus in the same location in the Different task and the alternation after four identical stimuli in the Same task). An anterior N2 was characteristic to the Nogo stimuli of the Different task. P3 latency was longer, and it had more anterior distribution to the Nogo stimuli.