Congruency and Distance Effects Vary Across Simultaneous and Sequential Two-Digit Integer, Fraction, and Decimal 2AFC Tasks

Two-alternative forced choice (2AFC) comparison tasks are widely used to investigate how humans process complex information. However, it remains not fully understood how the format of these tasks influences cognitive strategies. In this study, we examined this question within the number domain. We analyzed whether different 2AFC task formats provide converging information on how people process multi-component numbers (i.e., numbers composed of more than one part). In particular, we investigated how the distance and congruency effects—which are interpreted as behavioral markers of holistic and fragmented number processing—vary across simultaneous and sequential versions of two-digit integers, fractions, and decimals 2AFC tasks. Methods: Undergraduate students (n=162) completed both simultaneous and sequential versions of two-digit integer, fraction, and decimal comparison tasks. Comparison pairs varied in numerical distance (near vs. far) and congruency (congruent vs. incongruent). Results: Across all number types, we observed both distance and congruency effects. However, these effects differed by task format. In particular, a linear-mixed model revealed that the congruency effect was stronger in simultaneous tasks with near-distance pairs and weaker in sequential tasks with far-distance pairs. Discussion: The presence of both distance and congruency effects suggests that individuals combine holistic and fragmented processing strategies when comparing multi-component numbers. Furthermore, differences in the strength of the congruency effect across task formats indicate they play a critical role in shaping number processing strategies. Thus, our findings corroborate that simultaneous and sequential 2AFC tasks might engage distinct cognitive processes and should not be used interchangeably in numerical cognition research.