The component structure of event-related slow potentials: task, ISI, and warning stimulus effects on the 'E' wave

Two experiments were conducted to investigate the role of task variables and ISI length on the late component of the event-related slow potential (ERSP) recorded during various two-stimulus anticipation tasks. In the first experiment, a two-component ERSP was observed during short (1 sec) and long (4 sec) ISI conditions. The first component was generally Fz dominant and independent of task variables. The second component was generally Cz dominant and most prominent when an immediate motor response was required. A second experiment was successful in eliciting large second ERSP components even in the absence of response requirements. In this experiment, the topography of the second component was not exclusively Cz dominant; rather, it was task dependent, and achieved Fz dominance under delayed-response conditions. Heart rate, monitored concurrently with the EEG, also reflected the change in experimental conditions by the enhancement of a mid-ISI acceleratory component. The data are discussed with respect to a multiple-component model of slow potential activity during periods in which subjects anticipate significant events.