Rapid identification of handedness via motor variability of circular finger movements

Handedness is an important indicator of the brain’s functional lateralization, yet it is mainly assessed using subjective self-report inventories that are prone to ceiling effects and heavily skewed distributions. Here, we propose a rapid behavioral metric for identifying hand dominance based on the variability of circular index finger movements measured by a touch-sensitive smartphone screen. By quantifying the trajectory’s variability using shape similarity analysis, we show that the index finger of the dominant hand exhibits significantly smaller movement variability than the non-dominant one. In a study of 116 participants, this behavioral marker agreed with Edinburgh Handedness Inventory (EHI)-defined handedness in 94% of participants using eight seconds of movement data. Unlike the heavily skewed J-shaped distribution characteristic of the EHI, the difference in movement variability between the left and right fingers is approximately normally distributed. This provides a tool to quantify the degree of motor lateralization, offering a rapid behavioral method for identifying handedness using an accessible device.