How the Brain Process Stimulus-Response Conflict? New Insights from Lateralized Readiness Potentials Scalp Topography and Reaction Times

Abstract

Stimulus-Response Compatibility (SRC) refers to the fact that some tasks are performed easier and better than others because of the way stimuli and responses are paired with each other. To assess the brain responses to stimulus-response conflicts, we investigated the behavioral (accuracy and Reaction Times: RTs) as well as the physiological response (Lateralized Readiness Potentials: LRP) modulations in a positional blocked and a conditional mixed design in twelve university students. Results revealed that the performance was less accurate and the RTs, as well as the LRP onset, were delayed under the mixed conditional design. A greater compatibility effect was also noted on accuracy, RTs and LRP onset latency in the mixed design. Consistent with these findings, smaller peak activation at fronto-central areas suggests that more selective inhibition is needed in a mixed design context. Despite a smaller activation, the topographical distribution is similar in both designs. These results indicate that the translation time between stimulus- and response codes are greater under the mixed instruction, while the similar LRP topography suggests that common neural structures underlie LRPs in response to both type of designs.

Keywords: Lateralized Readiness Potentials; Mixed-Blocked Designs; Reaction Times; Stimulus Response-Compatibility.

Figure 1

Reaction times in function of compatibility, in comparing blocked and mixed designs.

Figure 2

Comparison of the SRC compatibility effect from the LRP onset latency, related to the correct activation in response to the mixed and blocked design.

Figure 3

Scalp distribution of the stimulus-locked LRP compatibility effect related to the blocked (panel A) and mixed design (panel B). For both panels, the solid bold line shows the LRPs to the incompatible, while the dashed line shows the LRPs in response to the compatible. The y-axis denotes the amplitude in microvolts, while the x-axis denotes the time scale in milliseconds. The vertical dashed lines refer to the stimulus onset, while the solid vertical line shows the mean reaction times (RTs) for each task. The negative polarity deflections denote the incorrect activation of the response while the positive deflections indicate the correct activation of the response.

Figure 4

Stimulus-locked LRP scalp distribution from lateralized locations showing the correct maximum activation (with standard error of the mean) to blocked and mixed designs (averaged across compatible-incompatible conditions). The figure show a design by electrode interaction found on the LRP peak amplitude. The LRP amplitude was larger in the blocked than in the mixed design at FC3′, C3′and CP3′ respectively.