§ Abstract
Individual differences in reasoning abilities reflect complex interactions between processing speed and executive control mechanisms, yet the unique contribution of executive functions remains contested. The Trail Making Test provides a critical opportunity to examine this relationship because Part B requires additional cognitive coordination beyond the basic processing speed demands of Part A. We examined whether cognitive complexity differences between Trail Making Test parts predict reasoning performance beyond shared associations with processing speed, working memory capacity, and age using proportional completion time ratios that address reaction time distributional concerns. Using two independent cognitive test batteries totaling 296,206 participants, we tested whether these complexity measures systematically predicted performance on grammatical reasoning and progressive matrices tasks through step-wise statistical modeling. Analyses revealed consistent small but reliable negative relationships between Trail Making complexity differences and both reasoning outcomes across independent samples. Participants showing greater proportional increases in completion time from Part A to Part B demonstrated poorer reasoning performance, with these modest effects replicating precisely across batteries using formal statistical equivalence procedures that test whether observed differences fall within meaningful bounds. The relationships persisted despite rigorous controls, indicating that executive coordination efficiency contributes systematically but proportionally to reasoning abilities beyond basic processing speed mechanisms. These findings advance theoretical understanding of the cognitive foundations of intelligence by providing robust evidence for specific, replicable executive function contributions to reasoning performance, though the small effect magnitudes suggest limited practical significance for real-world applications. The results inform cognitive assessment practices by validating Trail Making complexity measures as indicators of executive control processes that modestly affect higher-order cognitive abilities