The movement preparation of bimanual asymmetric reaching movements is longer than bimanual symmetric movements. This bimanual asymmetric cost is small for spatially cued movements and large with symbolic cues. Previous research on these bimanual asymmetric costs has relied on mean reaction time. The goal of the present study was to better understand the sensorimotor mechanisms of spatially and symbolically cued bimanual asymmetric costs by employing reaction time distribution analysis. Reaction time distributions were described with the ex-Gaussian parameters of \(\:\mu\:\) , \(\:\sigma\:\) , and \(\:\tau\:\) . Forty-eight young adults made bimanual symmetric and asymmetric reaching movements that were spatially or symbolically cued. With spatial cues, there was a small cost to \(\:\mu\:\) for bimanual asymmetric movements compared to symmetric ones. This was depicted as a 4.8 ms rightward shift to the reaction time distribution. The bimanual asymmetric cost with spatial cues is likely caused by the temporal coupling of bimanual asymmetric movements. With symbolic cues, there was a large cost to \(\:\mu\:\) and small costs to \(\:\sigma\:\) and \(\:\tau\:\) . This was depicted as the Gaussian and exponential components of the distribution having longer and more disperse reaction time for asymmetric movements. The bimanual asymmetric cost with symbolic cues is likely caused by two factors: stimulus-response translation of two different symbolic cues and temporal coupling of bimanual asymmetric movements. The bimanual asymmetric cost to µ with symbolic cues is likely a combination of both factors, with stimulus-response translation contributing more than temporal coupling. The bimanual asymmetric costs to σ and τ are exclusively caused by stimulus-response translation.
