Magnitude processing in young and older adults: Congruency between quantity and brightness.

Previous research suggests that dimensions such as space, time, and quantity are processed through a generalized magnitude system. Past evidence also shows that brightness can interact with numerical quantity. This study examined brightness-number interactions in young and older adults, and their modulations by stimulus-related factors (e.g., numerical ratio, item proportion) and domain-general mechanisms (e.g., executive control). Across four experiments using a numerical Stroop-like task, younger and older adults compared the numerical values of digit pairs varying in numerical magnitude and brightness (i.e., brighter vs. dimmer). Results revealed robust congruency effects (i.e., better performance when both dimensions matched) in both younger and older adults, consistent with the idea of shared magnitude representations across the lifespan. Additionally, congruency effects (a) increased for larger-ratio items, and (b) decreased in blocks with a high proportion of incongruent items. Data also revealed that (a) young and older adults had similar congruency effects, and (b) older adults showed smaller facilitation but larger interference effects in high-conflict conditions. These findings suggest that brightness operates as a magnitude dimension, and highlight the role of domain-general executive mechanisms (e.g., proactive control) in regulating magnitude processing across the lifespan.