Abstract
The rapid eye movements (saccades) used to transfer gaze between targets are examples of an action. The behaviour of saccades matches that of the slow–fast model of actions originally proposed by Zeeman. Here, we extend Zeeman’s model by incorporating an accumulator that represents the increase in certainty of the presence of a target, together with an integrator that converts a velocity command to a position command. The saccadic behaviour of several foveate species, including human, rhesus monkey and mouse, is replicated by the augmented model. Predictions of the linear stability of the saccadic system close to equilibrium are made, and it is shown that these could be tested by applying state-space reconstruction techniques to neurophysiological recordings. Moreover, each model equation describes behaviour that can be matched to specific classes of neurons found throughout the oculomotor system, and the implication of the model is that build-up, burst and omnipause neurons are found throughout the oculomotor pathway because they constitute the simplest circuit that can produce the motor commands required to specify the trajectories of motor actions.
Highlights
The rapid eye movements that transfer gaze from one object to another are referred to as saccades
To ensure that the experimental finding that the saccade velocity profile matches the profile of the neural signal y+ holds true, the orbital plant has to be supplied with an appropriate combination of a neural velocity signal, a neural position signal provided by the neural oculomotor integrator and a slide signal to compensate for the slower dynamics of the plant
It can be seen that the simulated results replicate the range of behaviours found in the human, rhesus monkey and rabbit, but the model was unable to accurately reproduce the eye movements of the mouse and cat, giving poorer approximations to the required relations between peak velocity and duration, as indicated by the significantly higher fitting error for these species
Summary
The rapid eye movements that transfer gaze from one object to another are referred to as saccades These discrete behaviours show a relatively invariant relationship between the size of the movement and its peak velocity and duration. We test whether this generic system of equations is applicable to saccadic eye movements, beginning with the hypothesis that the positive values of the variables x, y and z in Zeeman’s model correspond to the firing rates of the long-lead, medium-lead and omnipause cells in the brainstem, respectively. We augment Zeeman’s equations to model the charging process associated with the first stage of the saccade cycle, during which the specification of the required eye displacement builds up before the movement can start (Gancarz and Grossberg 1998). We conclude by exploring the testable neurophysiological implications of the model
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
