A technique for separating endogenous from exogenous human cortical potentials

In a temporal discrimination paradigm, if signal duration is the stimulus dimension to be discriminated, the moment of subject's decision can be manipulated by varying the duration of the target stimulus. As stimulus duration is lengthened, task-contingent potentials related to the decision process can be separated from those evoked by stimulus onset. Analysis of individual evoked responses indicates that 3 task-contingent components, occurring at 220, 300 and 340 msec are precisely time-locked to the moment of decision.