Voluntarily-generated unimanual preparation is associated with stopping success: evidence from LRP and lateralized mu ERD before the stop signal.

According to the race models of the stop-signal paradigm, stopping success (successful vs. unsuccessful stopping) is attributed to the finishing times of a go and a stop process. In addition to those factors involving processing times, in the present study we sought to use electrophysiological measures to find factors involving activations that could affect stopping success. We hypothesized that voluntarily-generated unimanual preparation would be a factor. To assess voluntarily-generated unimanual preparation in the stop-signal paradigm, we used a selective-stopping task without any precue. The selective-stopping task also allowed us to assess reaction times (RTs) even when stopping was successful. We demonstrated shorter RTs in signal-respond (i.e., unsuccessful stopping) than in signal-inhibit (successful stopping) trials, as is predicted by the race models. More importantly, we also demonstrated different pre-signal lateralized readiness potentials between the two types of trials and larger lateralized mu ERD in signal-respond than in signal-inhibit trials, suggesting that voluntarily-generated unimanual preparation affects stopping success. In addition to what is described in the race models of the stop-signal paradigm, the present results therefore demonstrated measures of pre-signal activations that could influence stopping success.

Locus of backward crosstalk effects on task 1 in a psychological refractory period task.

Our performance on a task decreases when the task is in a dual-task situation than when it is in isolation. An important experimental setting for dual-task situation is the psychological refractory period (PRP) paradigm, and the dual-task performance decrements in the PRP paradigm are referred to as PRP interference. The standard response-selection bottleneck (RSB) models state that the response-selection stage of the second task (T2) cannot start until the response-selection stage of the first task (T1) finishes, resulting in the PRP interference. Contrary to the prediction of RSB models, several researchers have found T2's modulations on T1's performance, and have suggested that T1's selection-related processes are affected by T2's selection-related processes, referred to as backward crosstalk effects. The locus of backward crosstalk effects is not clear, however, because RTs were measured in most previous studies. By using semantically unrelated stimuli and responses and by measuring T1's lateralized readiness potential, we examined the locus of backward crosstalk effects. We found that the interval between T1's stimulus onset and the stimulus-locked LRP onset was affected, suggesting T2's response selection starts before T1's selection is complete. The present result provided electrophysiological evidence focusing on T1's changes in favor of the hypothesis of parallel response selection in the PRP paradigm.

Signal-related contributions to stopping-interference effects in selective response inhibition.

In our ability to selectively inhibit a subset of concurrent response tendencies, referred to as selective response inhibition, stopping-interference (SI) effects have been found and attributed to global inhibitory processes. In the standard stop-signal paradigm, the stop signal might not only signal stopping but also produce other effects simply by virtue of being an additional signal. Therefore, we investigated whether previously observed SI effects reflect not only selective response inhibition but also other effects caused by the appearance of the stop signal. In Experiment 1, we controlled for the possible extra influences of the stop signal and still found SI effects, allowing a more confident attribution of SI effects to global inhibitory processes. Furthermore, the extra signal affected the motor system, as revealed by a reduction in SI effects on response force after the improved control. Using the lateralized readiness potential, Experiment 2 showed that the extra signal affected relatively central motor processing. The findings thus advance our knowledge about the distinction between signal-related and motor-inhibitory effects in stop-signal tasks.

Inhibitory effects on response force in the stop-signal paradigm.

The forcefulness of key press responses was measured in stop-all and selective stopping versions of the stop-signal paradigm. When stop signals were presented too late for participants to succeed in stopping their responses, response force was nonetheless reduced relative to trials in which no stop signal was presented. This effect shows that peripheral motor aspects of primary task responses can still be influenced by inhibition even when the stop signal arrives too late to prevent the response. It thus requires modification of race models in which responses in the presence of stop signals are either stopped completely or produced normally, depending on whether the responding or stopping process finishes first.

Nonselective motor-level changes associated with selective response inhibition: evidence from response force measurements.

In the present study, we examined the effects of selective response inhibition on motor production using response force measures within a task that was based on that of Aron and Verbruggen (Psychological Science, 19, 1146-1153, 2008). In each trial, participants were signaled to respond bimanually with the two index fingers or the two middle fingers. After a short delay, a stop signal was sometimes presented, indicating that one of the two finger responses should be withheld. A given response was slowed when the response on the other hand was stopped, replicating a previously observed stopping interference effect. In addition, the given response was also made more forcefully when the response on the other hand was stopped, indicating that the requirement to stop one activated response has global motor-level consequences for other responses that are to be carried out normally.