Abstract:
Previous research has indicated that two components of reaching behavior, initiation time and reach curvature, exhibit distinct patterns of trial sequence effects in congruency tasks. The observed patterns have been proposed to reflect two dissociable processes underlying decision behavior, with initiation times capturing the functioning of a threshold adjustment process involving the temporary inhibition of motor output, and reach curvatures reflecting a controlled selection process that supports goal-driven stimulus-response translation. The tasks used in previous studies, however, did not control for a range of associative-priming confounds commonly featured in congruency tasks. Consequently, the extent to which the observed patterns reflected the proposed processes or associative-priming confounds remained unclear. We therefore presented 45 adult participants with a reach-tracking version of the Stroop task that featured both confound-minimized and confound-laden trials. Initiation times revealed main effects of previous and current congruency on both confound-minimized and confound-laden trials, consistent with the claim that initiation times can be used to target the functioning of the threshold adjustment process. Conversely, reach curvatures exhibited a clear sensitivity to associative-priming effects, revealing a congruency sequence effect on confound-laden but not on confound-minimized trials. This finding is consistent with the claim that reach curvatures can be used to target the functioning of the controlled selection process. Thus, by directly evaluating the influence of associative-priming confounds, the present study revealed the strongest evidence to date that decision behavior in tasks involving conflict is fundamentally structured by the functioning of two dissociable processes.
