| Abstract: | ERPs were recorded during several RT tasks: simple RT; oddball choice RT; a LIE condition in which subjects were told stimuli would infrequently change, but did not; differential responding to two equiprobable stimuli that were randomized in one condition and alternated in another condition. Subtracting ERPs elicited during simple RT from those elicited during the other conditions, it was found that a negative component, NA, was enhanced, relative to simple RT, in all the other RT tasks. The data of the LIE condition indicated that NA was enhanced by the expectation that unpredictable stimulus changes would occur, even when they did not. The data of the 50/50 alternating RT condition indicated that stimulus changes by themselves enhance NA, even when they are predictable. There appear to be several deflections that comprise NA. NA was obtained with a variety of subtractions that balanced stimulus probability, the structure of the stimulus sequence and task instructions. Similar results were obtained whether subjects made a finger lift response or counted stimuli. |
