Abstract
Nature of variability in saccades. J Neurophysiol 90: 12–20, 2003. First published February
12, 2003; 10.1152/jn.01075.2002. We studied the variability in saccades by comparing the peak velocities of saccades with the same
target amplitude made with different actual amplitudes. We tested
three hypotheses: the pulse-height noise hypothesis (peak velocity and
amplitude vary proportionally), the localization noise hypothesis
(variability in amplitude and peak velocity lie along the main sequence), and the independent noise hypothesis (variability in amplitude and peak velocity are independent). We measured eye orientation
in two experiments by a scleral coil and a video system. Surprisingly,
the main source of variability of saccades depended on the measurement system used. A combination of localization noise and indepen-
dent noise best describes the data obtained by the video system. The
independent noise (e.g., measurement inaccuracy) was the main
source of variability. For the scleral coils, the variability was considerably larger than for the less accurate video system. The pulse-height
noise hypothesis best describes this additional variability. Therefore
we conclude that pulse-height noise is the main source of variability
in saccades measured with scleral coils. We discuss the influence of
scleral coils on saccade generation and suggest that a change in motor
strategy due to the discomfort of wearing the coils might be the cause
of the increased variability.
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