Physical exertion impairs individual representation while preserving mean representation in visual short-term memory

Perceptual averaging, a fundamental mechanism of visual short-term memory (VSTM), enables automatic extraction of the ensemble mean from similar visual stimuli. While concurrent physical exertion is known to impair VSTM, its impact on this ensemble-coding ability remains unclear. To address this gap, the current study employed a dual-task paradigm combining facial expression recognition with concurrent isometric handgrip contractions. Participants memorized four facial expressions and then classified a face probe as a set member or not while maintaining either 5% or 40% of their maximum force (low vs. high physical load). Results revealed that high physical load reduced hit rate and discriminability (d') while increasing false alarm rate, indicating impaired memory performance. However, recognition accuracy for probes that were the mean of the set and the fitted Gaussian parameter σ (reflecting the precision of mean representation) remained unchanged across load conditions, suggesting that mean representation was unaffected by concurrent physical exertion. These findings indicate that while concurrent physical exertion disrupts item-specific memory-that is, individual representation in VSTM-primarily due to shared attentional resource competition between physical action and cognitive processing, perceptual averaging-that is, mean representation in VSTM-remains resilient to dual-task interference, underscoring its stability and robustness in VSTM functioning.