Neural correlates of the Simon effect modulated by practice with spatial mapping

Practice effects vs. transfer effects in the Simon task

The Simon effect refers to the fact that, even though stimulus position is task-irrelevant, responses to a task-relevant stimulus dimension are faster and more accurate when the stimulus and response spatially correspond than when they do not. Although the Simon effect is a very robust phenomenon, it is modulated by practice or transfer from previous tasks. Practice refers to the modulation of the Simon effect as a function of number of trials. Transfer refers to the modulation of the Simon effect as a function of preceding tasks. The aim of the present study is to disentangle the role of practice and transfer in modulating the Simon effect and to investigate whether such modulation can be extended to a different response modality. Three experiments were conducted, which included three sessions: the Baseline session, the Inducer session and the Diagnostic session. The task performed in the Baseline and the Diagnostic sessions were comprised of location-irrelevant trials (i.e., they were Simon tasks). The task performed in the Inducer session required performing location-relevant trials (i.e., it was a spatial compatibility task with a compatible or an incompatible stimulus–response mapping). In the first and third experiments, participants were required to respond manually in all sessions. In the second experiment, the task performed in the Inducer session required manual response, while in the Baseline and Diagnostic sessions the tasks required ocular response. Results showed a reduced-Diagnostic Simon effect after both compatible and incompatible mapping in the Inducer session, regardless of whether response modality was the same or different. These results support the notion that the practice effect prevails over the transfer effect.

From eyes to hands: Transfer of learning in the Simon task across motor effectors

Inhibition of irrelevant and conflicting information and responses is crucial for goal-directed behaviour and adaptive functioning. In the Simon task, for example, responses are slowed if their mappings are spatially incongruent with stimuli that must be discriminated on a nonspatial dimension. Previous work has shown that practice with incongruent spatial mappings can reduce or even reverse the Simon effect. We asked whether such practice transfers between the manual and oculomotor systems and if so to what extent this occurs across a range of behavioural tasks. In two experiments, one cohort of participants underwent anti-saccade training, during which they repeatedly inhibited the reflexive impulse to look toward a briefly presented target. Additionally, two active-control training groups were included, in which participants either trained on Pro-saccade or Fixation training regimens. In Experiment 1, we probed whether the Simon effect and another inhibitory paradigm, the Stroop task, showed differential effects after training. In Experiment 2, we included a larger battery of inhibitory tasks (Simon, Stroop, flanker and stop-signal) and noninhibitory control measures (multitasking and visual search) to assess the limits of transfer. All three training regimens led to behavioural improvements in the trained-upon task, but only the anti-saccade training group displayed benefits that transferred to the manual response modality. This transfer of training benefit replicated across the two experiments but was restricted to the Simon effect. Evidence for transfer of inhibition training across motor systems offers important insights into the nature of stimulus-response representations and their malleability.

Practice-induced and sequential modulations in the Simon task: evidence from pupil dilation

Recent evidence showed that pupil dilation (PD) reflects modulations in the magnitude of the Simon interference effect due to correspondence sequence. In the present study we used this measure to assess whether these modulations, thought to result from cognitive control mechanisms, are influenced by prior practice with an incompatible stimulus-response (S-R) mapping. To this end, PD and reaction times (RTs) were recorded while participants performed a Simon task before and after executing a spatially incompatible practice. The sequential analysis revealed that PD mirrored the conflict-adaptation pattern observed in RTs. Crucially, sequential modulations were not affected by prior practice. These findings support the view that the modulations of the Simon effect due to prior practice and those due to correspondence sequence result from two different mechanisms, and suggest that PD can help to better understand the mechanisms underlying response selection and cognitive control in the Simon task.

Event-related lateralized readiness potential correlates of the emotion-priming Simon effect

The Simon effect indicates that the reaction time (RT) is shorter when the stimulus and response locations are congruent than when they are not. This study used a priming-target paradigm to explore the emotion-priming Simon effect with event-related potential techniques. The technique of residue iteration decomposition was employed to analyze the lateralized readiness potential (LRP) component, which contributed to disentangling the overlap between LRP and N2 central contralateral in the Simon task with horizontal stimulus-response arrangements. The behavioral result revealed significant Simon effect in RT. In the neural process, the Simon effect was reflected by both the stimulus-locked LRP (S-LRP) and the response-locked LRP (R-LRP), with the incongruent condition showing longer onset latency, larger Gratton-dip, and smaller negative-going deflection of S-LRP and smaller negative-going deflection of R-LRP. These findings suggest that the interference of irrelevant location information is located at the perceptual-encoding (indicated by S-LRP) and response-execution stages (indicated by R-LRP), providing evidence for both the perceptual-interference and response-interference accounts. However, the further linear regression result signaled that the Simon effect might be more closely related to the response-execution stage than the perceptual-encoding stage. In addition, the influence of emotion on the Simon effect was salient only in the incongruent condition, showing longer onset latency of S-LRP and larger Gratton-dip of R-LRP in the negative emotion-priming condition than in the neutral emotion-priming condition, which revealed that the emotional interference effect arose from the stages of perceptual encoding and early response execution only when the locations of a stimulus and the corresponding response were incongruent.