Stream segregation reduces the subdivision cost in auditory-motor synchronized tapping

The synchronization of body movements with auditory beats, often studied through finger-tapping tasks, involves complex interactions between anticipation and motor planning. The present study examines the subdivision cost in synchronized tapping tasks and investigates whether the structure of tone sequences influences this cost. Sixteen participants performed synchronized tapping tasks with auditory stimuli arranged in sequences (ABA_ABA_ ...) designed to induce stream segregation, which is a phenomenon where the brain organizes sounds into integrated/separated streams. Temporal asynchrony between the onset of stimuli and tapping was calculated, and its mean and standard deviation (SD) were analyzed to evaluate the accuracy and stability of synchronized tapping. Results indicated that while the mean temporal asynchrony showed negative values across conditions, the subdivision effect was not evident in the accuracy of tapping. However, the SD of temporal asynchrony revealed significant effects. At the inter-tap interval (ITI) of 1200 ms, the control condition had higher SDs than the segregated conditions. Conversely, at the ITI of 400 ms, segregation conditions showed higher SDs than the control condition, indicating a subdivision cost. Notably, the tone sequence with a wide frequency range was more stable than that with a narrow frequency range at the ITI of 400 ms. This study demonstrates that the structure of tone sequences significantly affects the subdivision cost in synchronized tapping tasks, particularly at short ITIs. These findings provide valuable insights into the neural mechanisms underlying auditory-motor synchronization and suggests potential applications in rhythm training and rehabilitation for individuals with motor disorders.