Response Inhibition in a New "Stroop-Matching/Stop-Signal" Protocol Corroborates the Assumptions Predicted by the Horse-Race Model

Inhibition is a broad construct referring to a set of functions responsible for suppressing stimuli or responses to prioritize more relevant ones. Several paradigms were used to assess different types of inhibition, such as the stop-signal and Stroop-like tasks. The horse-race model is the main theorical model that supports the stop-signal paradigm, which postulates that response inhibition depends on a competition between the processes involved in the emission and inhibition of a motor response. We investigated the assumptions of the horse-race model using a novel primary-task with different levels of difficulty (the Stroop-matching task) to understand how the stop-signal task performance varied according to the demands imposed by the different Stroop conditions. ANOVAs and planned comparisons revealed that the motor inhibition, assessed by inhibition rates and the inhibition-errors rates were influenced by the primary task reaction times (RTs) obtained in the different Stroop conditions. These results confirm that the primary task demand is a major factor that influences response execution/inhibition in a stop-signal protocol. Moreover, they corroborate the horse-race model even under this new approach in which the primary task was not represented by a simple detection task, but instead required interference control. Altogether, our data indicate the potential use of our "Stroop/Stop" protocol to investigate the interaction between different inhibitory processes involved in each task and elucidate the relationship between different types of inhibition. Public Significance Statement This study investigates the assumptions of the horse-race model, commonly used to explain the results obtained in stop-signal tasks using a protocol that combined Stroop-matching and stop-signal tasks. Inhibition rates and inhibition-error rates revealed interaction between the different inhibitory mechanisms in the tasks. Results indicate the potential use of the current protocol to investigate the inhibitory functions involved in different tasks to better understand the concept of inhibition.