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A new method based on jackknifing is presented for measuring the difference between two conditions in the onset latencies of the lateralized readiness potential (LRP). The method can be used with both stimulus- and response-locked LRPs, and simulations indicate that it provides accurate estimates of onset latency differences in many common experimental conditions.

Many reaction time (RT) researchers truncate their data sets, excluding as spurious all RTs falling outside a prespecified range. Such truncation can introduce bias because extreme but valid RTs may be excluded. This article examines biasing effects of truncation under various assumptions about the underlying distributions of valid and spurious RTs. For the mean, median, standard deviation, and skewness of RT, truncation bias is larger than some often-studied experimental effects. Truncation can also seriously distort linear relations between RT and an independent variable, additive RT patterns in factorial designs, and hazard functions, but it has little effect on statistical power. The authors report a promising maximum likelihood procedure for estimating properties of an untruncated distribution from a truncated sample and present in an appendix a set of procedures to control for truncation biases when testing hypotheses.

Miller, Patterson, and Ulrich (1998) introduced a jackknife-based method for measuring the differences between two conditions in the onset latencies of the lateralized readiness potential (LRP). The present paper generalizes such jackknife-based methods to factorial experiments with any combination of within- and between subjects factors. Specifically, we introduce a subsample scoring method to assess potential main and interaction effects on LRP onsets within conventional yet slightly adjusted analyses of variance (ANOVAs) and post hoc comparison procedures.

Response speed to a signal is faster when advance information about the forthcoming movement is provided before signal onset. Although this precuing effect is well established, the location of this saving in reaction time (RT) in the information-processing system is controversial. Some authors have claimed that the precuing effect resides at a motoric level, whereas others have suggested a nonmotoric locus. The present experiments used onset latencies of the lateralized readiness potential (LRP) to locate the precuing effect. The results of 2 experiments with a highly compatible (Experiment 1) and with an incompatible (Experiment 2) stimulus-response mapping indicate that this effect resides, at least partially, in the motoric portion of RT. In addition, the LRP amplitude before signal appearance increased with the amount of advance information, supporting a muscle-specific preparation hypothesis.

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This article assesses whether the two-alternative forced-choice (2AFC) and the reminder tasks (i.e., method of constant stimuli) yield identical estimates of the difference limen (DL). In a series of six experiments, participants discriminated between two duration stimuli. Experiments 1-5 employed auditory stimuli, and Experiment 6 employed visual stimuli. Experiments 1 and 2 combined each of the two tasks with an adaptive and a nonadaptive procedure for threshold estimation. Experiment 3 varied the distribution of the comparison levels, whereas Experiment 4 employed random interstimulus intervals. Experiments 5 and 6 examined the influence of the presentation order of the standard and comparison stimuli. Results indicate that both the adaptive and the nonadaptive procedures yield virtually identical DL estimates; yet, the 2AFC task produces consistently larger DLs than does the reminder task. In addition, DL increases when the standard occurs in the second rather than in the first stimulus position. In order to account for these results, we assume that participants use an internal standard instead of the actually presented standard as a reference for their judgment.

Miller, Patterson, and Ulrich (1998) introduced a jackknife-based method for measuring the differences between two conditions in the onset latencies of the lateralized readiness potential (LRP). The present paper generalizes such jackknife-based methods to factorial experiments with any combination of within- and between subjects factors. Specifically, we introduce a subsample scoring method to assess potential main and interaction effects on LRP onsets within conventional yet slightly adjusted analyses of variance (ANOVAs) and post hoc comparison procedures.