Perceptual target discriminability modulates the Simon effect beyond the fading of distractor-based activation: Insights from delta plots and diffusion model analyses.

Abstract

The visual Simon task is widely employed to explore the underlying mechanisms of sensorimotor processing in the presence of task-relevant (targets) and task-irrelevant (distracting) location information. Critically, the Simon effect is considered as an indicator of action-related interference resulting from distractor-based activation, which fades out over time. In this study, we tested whether attenuated Simon effects with slower task processing may be fully explained by the fading of distractor-based response activation. To that end, we selectively manipulated perceptual target discriminability by varying the ratio of differently colored dots within (Experiment 1) and between blocks (Experiment 2). According to pure fading activation accounts, the negative-going delta plots of the two discriminability conditions should overlap across the entire reaction time (RT) distribution. In contrast to this prediction, the negative-going DPs for the two discriminability conditions did not overlap in either experiment. Instead, the Simon effect was either consistently smaller (Experiment 1) or larger (Experiment 2) across the entire RT distribution in the easy condition compared to the hard condition. This result pattern indicates that perceptual target discriminability affected conflict resolution beyond the mere fading of distractor-based activation. Exploratory model-based analyses suggest a stronger processing of relevant perceptual information with more discriminable targets, which may counteract the influence of distracting location information. However, as the exact effects of discriminability on conflict processing seem to depend on variation mode (trialwise vs. blockwise), the importance of global strategic effects is also highlighted. Public Significance StatementIn various real-world situations, individuals face the challenge of processing goal-relevant sensory information in environments filled with distracting and potentially conflicting sources of information. Uncovering the underlying mental mechanisms enabling the successful transformation of information into appropriate motor responses is of both practical (e.g., human-machine-interaction) and theoretical (uncovering general principles of human cognition) importance. In the present study, we demonstrate that the strength of activation by relevant information directly influences action-related conflict. These findings offer new evidence, suggesting a more substantial involvement of perceptual processes in action control than previously thought.