The flexibility of the mental timeline: The influence of motion direction on the STEARC Effect

Spatial representations of time, as reflected in the STEARC effect, suggest that shorter durations are associated with left space and longer durations with right space. While such mappings are often considered stable, recent evidence indicates that they may be context-dependent. The present study investigated whether motion direction influences the STEARC effect, thereby testing the flexibility of the mental timeline. Two experiments were conducted using a 2 × 2 × 2 within-subject design manipulating Duration (short vs. long), Motion Direction (leftward vs. rightward), and Response Side (left vs. right). In Experiment 1, motion direction varied randomly, whereas in Experiment 2 it was blocked. Results showed that in Experiment 1, the STEARC effect was not observed, and performance was instead driven by spatial compatibility between motion direction and response side. In Experiment 2, no significant STEARC effect emerged; however, descriptive patterns indicated a tendency toward a reversed spatial–temporal mapping under predictable motion conditions. These findings suggest that the mental timeline is not a fixed representation but a flexible system modulated by dynamic spatial cues and task structure.