Arm movement and gap as factors influencing the reaction time of the second saccade in a double-step task
L. Lünenburger & K.-P. Hoffmann
European Journal of Neuroscience, 17: 2481-2491, 2003.
- To guide our hand for reaching, we explore our visual environment by sequences of saccades. In the present
paper, we studied the eye and hand movements of human subjects looking or looking and pointing at a target that
is instantaneously displaced two times (double-step task). It was previously shown that the second saccade has
a much longer reaction time than the first one [Feinstein & Williams (1972) Vision Res., 12, 33-44]. The second
reaction time is even longer if the subject also has to point to the target with the hand [Lünenburger et
al. (2000) Eur. J. Neurosci., 12, 4107-4116]. The conditions and objective for these effects are further examined
in the present paper. It is shown that vision of the hand reduces the first and second saccadic reaction times
in parallel. The second reaction
time is prolonged for shorter delays between both target steps as well as for larger amplitudes of the second saccade.
However, the long second reaction time does not reflect an absolute saccadic refractory period, because a gap before
the second target step reduces the second reaction time to a value similar to the first. Hand response time and
average hand velocity were increased when the second target step was larger. The response time for the eyes was
about 30% of the response time of the hand. We argue that the observed effects reflect the coordination of eye
and hand movement to allow a precise and efficient reaching behaviour.
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