The Stroop-matching task is a variation of the Stroop task in which participants have to compare a Stroop stimulus attribute (color or word) to a second stimulus. The Stroop-matching response conflict (SMRC) represents an interference related to the processes involved in selection/execution of manual responses. In the present study, we developed a variation of the Stroop-matching task in which the Stroop stimuli were matched to graspable objects (a cup) with intact or broken handles laterally oriented (Experiment 1) or to colored bars laterally presented (Experiment 2). It allowed testing the presence of the correspondence effect for lateralized handles and bars and its possible influence on SMRC. Two different intervals (100 and 800 ms) were also included to investigate time modulations in behavioral performance (reaction time and accuracy). Fifty-five volunteers participated in the study. In both experiments, significant SMRC was found, but no interaction occurred between SMRC and correspondence effect, supporting that the hypothesis of different and relatively independent psychological mechanisms is at the basis of each effect. Because significant facilitation for ipsilateral motor responses (correspondence effect) occurred for graspable objects but not for lateralized bars, the attentional shift/spatial-coding view was not able to completely explain our data, and therefore, the grasping affordance hypothesis remained as the most plausible explanation. The time course of facilitation observed in the first experiment and by others indicates the importance of further studies to better understand the time dynamic of facilitation/inhibition of motor responses induced by graspable objects.
