The Reverse Distance Effect in Ordinal Processing of Repeated Item Sequences.

Ordinal processing is a core component of numerical cognition, and its behavioral signature is the Reverse Distance Effect (RDE). However, previous studies indicate that the RDE is influenced by sequence composition, and it is unclear whether it is similarly affected by sequence types. Prior research has largely focused on non-repeating sequences (e.g., 1-2-3), while the processing of repeated item sequences (i.e., non-strict sequences; e.g., 1-2-2-3) remains unexplored. Experiment 1 (numbers) showed a significant RDE in the first and last repetition conditions. However, the middle repetition condition resulted in a null effect, suggesting that the middle repeated item interferes differentially with ordinal representation. In contrast, Experiment 2 (letters) showed a significant RDE regardless of repetition position. Overall, the RDE extends to repeated item sequences when interference is comparable between distance conditions. Moreover, the presence of the RDE in the letter task indicates that the effect observed in repeated item sequences extends to non-numerical materials. This study provides the first systematic investigation of repeated item sequences, highlighting the role of repeated items in order judgment and expanding the scope of ordinal processing research.