EFFECTS OF TASK VARIABLES ON MEASURES OF THE MEAN ONSET LATENCY OF LRP DEPEND ON THE SCORING METHOD

The lateralized readiness potential (LRP) can be used to index the sta rt of response activation. The onset of the average LRP can be compute d as the latency at which the component starts to deviate significantl y from zero or as the latency at which a certain proportion of its max imum amplitude is attained. The properties of both measures as estimat es of the mean onset latency of the LRP were examined. Experiment 1 wa s a simulation study in which the mean onset latencies were known. Res ults indicated different types of bias for the two measures and greate r reliability for a proportional measure. In Experiment 2, the sensiti vity to bias, consistency, and linearity of both measures were evaluat ed in a set of empirical data. By all three criteria, a proportional o nset measure was superior. It is recommended that the choice of the me asure should depend on the hypothesis to be tested, so that conclusion s are based on the more conservative test.