Decomposing delta plots: exploring the time course of the congruency effect using inhibition and facilitation curves.

Abstract

When assessing the time-course of evidence accrual in conflict tasks, delta plots are often employed to show the time course of congruency effects. However, delta plots on reaction time and response errors only capture the differences between the congruent and incongruent conditions, detailing that a pattern or shift is occurring, but not what contributes to creating these changes. To gain a clearer idea of what is causing these trends and shifts, the neutral condition can be added to conflict tasks in order to decompose the congruency effect into two components: facilitation and inhibition. Similarly, the traditional delta plot of the congruency effect can also be decomposed to capture the time-course of facilitation and inhibition in separate curves. Thus, this article endeavored to both assess the utility of inhibition and facilitation curves as a tool for parsing apart the congruency effect, and also to see how the observed patterns changed on a larger time frame. To do this, an exploratory study was conducted on three conflict task experiments (a linguistic flanker task, numeric Stroop task, and symbolic Simon task) that were run with a speed-accuracy tradeoff measure implemented as well. By observing the conflict tasks at various speed stresses, we hoped to evaluate how, or if, inhibition and facilitation change at different response thresholds. The addition of delta functions for facilitation and inhibition provided further insight into base mean RT data. The results also provided evidence for numerous assumptions regarding cognitive control, such as a dominant effect of inhibition driving most of the congruency effect.