The main sequence of saccades optimizes speed-accuracy trade-off.
In primates, it is well known that there is a consistent relationship between the duration, peak velocity and amplitude of saccadic eye movements, known as the 'main sequence'. The reason why such a stereotyped relationship evolved is unknown. We propose that a fundamental constraint on the deployment of foveal vision lies in the motor system that is perturbed by signal-dependent noise (proportional noise) on the motor command. This noise imposes a compromise between the speed and accuracy of an eye movement. We propose that saccade trajectories have evolved to optimize a trade-off between the accuracy and duration of the movement. Taking a semi-analytical approach we use Pontryagin's minimum principle to show that there is an optimal trajectory for a given amplitude and duration; and that there is an optimal duration for a given amplitude. It follows that the peak velocity is also fixed for a given amplitude. These predictions are in good agreement with observed saccade trajectories and the main sequence. Moreover, this model predicts a small saccadic dead-zone in which it is better to stay eccentric of target than make a saccade onto target. We conclude that the main sequence has evolved as a strategy to optimize the trade-off between accuracy and speed.
SensoriMotor Laboratory, Centre for Theoretical and Computational Neuroscience, University of Plymouth, Plymouth, PL4 8AA, UK. cmharris@plymouth.ac.uk
Christopher M
CM
Harris
Daniel M
DM
Wolpert
D000818:Animals; D001921:Brain / Q000502:physiology; D005403:Fixation, Ocular / Q000502:physiology*; D006801:Humans; D008959:Models, Neurological; D009434:Neural Pathways / Q000502:physiology; D009801:Oculomotor Muscles / Q000294:innervation / Q000502:physiology; D011597:Psychomotor Performance / Q000502:physiology*; D011930:Reaction Time / Q000502:physiology*; D012438:Saccades / Q000502:physiology*; D013997:Time Factors