Influence of arm movements on saccades in humans.
L. Lünenburger, D. Kutz & K.-P. Hoffmann
European Journal of Neuroscience, 12: 4107-4116, 2000
- When reaching for an object we usually look at it before we touch it with the hand. This often unconscious
eye movement prior to the arm movement allows guiding of the final part of the hand trajectory by visual feedback.
We examined the temporal and spatial coordination of this control system by psychophysical measurements of eye
and arm movements of naive human subjects looking or looking and pointing as fast as possible to visual targets
in physical and virtual-reality setups. The reaction times of saccades to a step-displaced target were reduced,
and the number of corrective saccades decreased, when the subject had to produce acorresponding simultaneous hand
movement to the same target. The saccadic reaction time was increased when saccade and hand movement went in opposite
directions. In a double-step task the reaction time for the second saccade was longer than for the first. Co-use
of the hand leads to an additional increase of saccadic reaction time. Taken together this study shows an improvement
in initial saccades if they are accompanied by hand movements to the same target. This effect might ensure that
the reach target is foveated early and accurately enough to support the visual feedback control of the hand near
the target. Longer reaction times for the second saccade to double-step displaced targets might reflect a saccadic
refractory time intensified by simultaneous arm movements. These
results are discussed in the light of recent findings from our laboratory
on saccade- and reach-related neurons in the superior colliculus of
macaque monkeys.
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