You react faster when the button matches the side a sound came from

Even when which ear a sound comes from is completely irrelevant to the task, people respond faster and more accurately when their answer button is on the same side as the sound. J. R. Simon and A. P. Rudell documented this in 1967: spatial location automatically primes a response, whether or not it has anything to do with the task.

— J. R. Simon and A. P. Rudell, Auditory S-R Compatibility: The Effect of an Irrelevant Cue on Information Processing — Journal of Applied Psychology, 51(3), 1967