Visually guided eye and hand movements in man

Reaction times of saccades and of hand movements to a single visual target were measured and correlated on a trial-by-trial basis. The absolute values of the reaction times and their correlations depend on whether the fixation point, from which both eye and pointing movement started, remained visible (overlap) or was turned off some time before the target appeared (gap). Under overlap conditions long reaction times were obtained exhibiting large scatter and high correlations. Under gap conditions short reaction times (including express saccades) occurred with a small scatter and almost no correlations. It is concluded that the preparation of the saccade must be completed before the corresponding pointing movement can be initiated but not vice versa.