Author(s): KAWABE, S.2, MURAKAMI, H.1, YAMADA, N., Institution: CHUKYO UNIVERSITY, Country: JAPAN, Abstract-ID: 1770

Introduction
Temporal unpredictability in competitive contexts increases decisional complexity. This study examined how temporal uncertainty, structured according to Shannon entropy principles, influences the distribution of reaction time (RT) in a button-press task simulating kendo movements under rapid decision-making demands.

Methods
Eleven participants pressed designated keys as quickly as possible in response to screen stimuli. Two stimuli were used: a preparatory stimulus (white circle) and a main stimulus (red circle). The preparatory stimulus was presented 7–11 times consecutively, followed by the main stimulus on the 8th–12th presentation. Temporal uncertainty was manipulated by varying the range of inter-stimulus intervals (low: 450–550 ms; medium: 400–600 ms; high: 300–800 ms), informed by Shannon entropy principles. Six condition sequences were analyzed as a preliminary dataset to explore distributional tendencies across entropy-informed temporal uncertainty conditions. Participants pressed the “K” key for the preparatory stimulus and selected either the “J” (attack) or “L” (defense) key for the main stimulus. For right-handed participants, “J” was pressed with the index finger and “L” with the ring finger; assignments were reversed for left-handed participants. Response success was defined by RT. In the attack condition, responses between 0.10–0.29 s were successful; <0.10 s or ≥0.30 s were unsuccessful. In the defense condition, responses between 0.30–0.35 s were successful; <0.30 s or ≥0.35 s were unsuccessful. Success thresholds were determined based on task-specific timing constraints designed to discourage anticipatory or random responses.

Results
Mean RT did not differ across entropy conditions (0.33 s in all). However, the proportion of delayed responses (> 0.40 s) increased under high temporal uncertainty (15.4 %) compared with low (10.6 %) and medium (9.2 %) conditions, indicating distributional instability despite stable mean performance.

Conclusion
No differences in mean RT were observed among conditions; however, under high uncertainty, the proportion of delayed responses increased, suggesting a possible influence on the reaction time distribution. These findings indicate that temporal uncertainty destabilizes response timing without altering average speed, suggesting altered temporal preparation under entropy-informed conditions.