Prior studies indicate that loudness and number magnitude influence the processing of each other (e.g. Hartmann & Mast, 2017). This influence is typically explained by the assumption that loudness and numbers are represented on a generalized magnitude representation system (e.g. A Theory of Magnitude, Walsh, 2003). To draw further conclusions about the underlying processes, I investigated the loudness-number interaction in speeded-discrimination tasks with regard to the influence of distance and bidirectionality in two different experiments. In experiment 1 (N = 32), participants decided whether a visually presented number was larger or smaller than five and simultaneously heard a loud or soft tone with different loudness distances to a fixed intermediate loudness level. Experiment 2 (N = 32) was a cued task-switching paradigm in which participants switched between a loudness and a number classification task. Distance to an implicit standard was varied in both dimensions.
There was a significant interaction between loudness and number magnitude in both experiments with shorter reaction times in congruent trials (loud tone and large number or soft tone and small number) compared to incongruent trials. This interaction was present in the loudness and number classification task indicating a bidirectional influence between both dimensions. With regard to the influence of distance, only loudness distance modulated the loudness-number interaction and the effect differed between both experiments and tasks. I will discuss the results with regard to potential processes underlying loudness-number interactions and the implications for an assumed generalized magnitude representation system.