Late components of saccade-related brain potentials in guessing tasks.

The late positive components of lambda responses were studied in a guessing task modified in such a way that subjects had to perform a saccadic eye movement in order to perceive task-relevant information. Responses from 6 scalp areas were investigated in 9 subjects and in 2 conditions: control and guessing. In both conditions subjects performed two consecutive saccades in a given trial: the first to the middle light, the second to the target area. In the control condition the subjects knew beforehand what the 'target' would be. In the guessing condition they had to make a guess before each trial as to which of the three target stimuli would appear. The target stimuli occurred with unequal probability and were presented in a randomized sequence. Unlike the control condition, the guessing task led to the appearance of a late positive component in the lambda response. Similar to traditional ERP findings, this late positivity showed an amplitude maximum at the parietal area and a peak latency at 375 msec from saccade onset. Furthermore, Principal Component-Varimax Analysis (PCVA) of the lambda responses revealed a first factor giving the strongest loading in the latency range of the P300, and a second factor which was identified as the slow wave. These factors are quite similar to the factors found in the PCVA of ERPs. Our results suggest that the late components of lambda responses reflect the effects of information processing in cognitive tasks similarly to the way the late positive components of ERPs do.