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 start of response activation. The onset of the average LRP can be computed as the latency at which the component starts to deviate significantly from zero or as the latency at which a certain proportion of its maximum amplitude is attained. The properties of both measures as estimates of the mean onset latency of the LRP were examined. Experiment 1 was a simulation study in which the mean onset latencies were known. Results indicated different types of bias for the two measures and greater reliability for a proportional measure. In Experiment 2, the sensitivity to bias, consistency, and linearity of both measures were evaluated in a set of empirical data. By all three criteria, a proportional onset measure was superior. It is recommended that the choice of the measure should depend on the hypothesis to be tested, so that conclusions are based on the more conservative test.