Horizontal Saccadic Eye Movements to Visual and Auditory

Goal-oriented human saccades were recorded under double-step paradigm. The stimuli consisted of either visual or auditory-visual bi-sensory targets. Eye movement data were analyzed based on a 3rd-order linear horizontal saccadic eye movement model, where the inputs to the muscle were agonist and antagonist active-state tensions that were described by pulse-slide-step waveforms with a post inhibitory rebound burst (PIRB) based on a timeoptimal controller. 

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Parameter estimations were calculated using the system identification technique for saccade parameters and neural inputs. Saccade amplitude transition function (ATF) and response latency indicated the saccade programming mechanism. 

The responses were affected by when the second peripheral target was presented. The neural input estimations supported the responsive neuron populations in the superior colliculus under different stimulus conditions, and indicated the double-step visual or auditory-visual stimulus may affect the synchrony of neuron firing. The study described here expanded our previous work and further supported the muscle model as well as the theory of the time-optimal saccade controller under physiological constraints.Read More...

Visually Guided Horizontal Saccades under the Double-Step Paradigm

Visually goal-oriented saccades were recorded under the double-step paradigm. Data were analyzed to produce parameter estimates using the system identification technique for a 3rd-order linear horizontal saccadic eye movement model. Statistical analysis of a large human saccade data set provided reliable conclusions of the response properties. 

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Saccade amplitude, latency and inter-saccade interval were discussed with time delay, indicating the parallel programming mechanism, which two saccades to different targets could be programmed simultaneously. The results of neural input estimations suggested that the double-step visual targets may affect the synchronous firing of the saccade responsible neurons in the superior colliculus.

Saccades are the fastest eye movements that enable us to rapidly redirect our line of sight from one target to another one. They are conjugate and ballistic, with a typical duration of 30-100 ms and a latency of 100-300 ms when triggered by visual stimuli. The latency is thought to be the time interval during which the CNS determines whether to make a saccade, and, if so, calculates the distance the eyeball is to be moved, transforming retinal errors into transient muscle activity. Read More.....

Linear Quadratic Tracking Control of Smooth Pursuit Eye Movements

Conventional feedback control models of the oculomotor system fail to account for the destabilizing effects of neural transmission delays. To address this shortcoming, a linear quadratic tracking algorithm used to control smoothly pursuing eye movements of various target trajectories is presented. Based on the type of input to the system, it is shown that stability, in the presence of large motor feedback delays, can be maintained by modulating weighting factors intrinsic to the model. 

Conditions, such as the initial orientation of the eye relative to the location of where a target first becomes salient and the possible oscillatory nature that the reference trajectory may present, play important roles in determining the optimal cost to go motor control strategy at the onset of a tracking movement.

Human perception is the process of acquiring, interpreting, selecting and organizing sensory information to effectively interact with the environment. It is argued that the ability to perceive and direct visual attention to an object that warrants more detailed analysis is the most important of the senses. The oculomotor system has evolved to serve this purpose and, consequently, has important communicative value for studying neuromuscular integration.

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Research involving sensorimotor control seeks to answer the fundamental question: How does our brain select inputs to produce a desired intention and manifest it in the form of movement. The difficulty associated with this question becomes more apparent for multi-body, multi-dimensional systems whose equations of motion are nonlinear and coupled. Since the eye is confined to three rotational degrees of freedom, and because the actions of its extraocular muscles are direct, the oculomotor system provides an initial context for gaining insight into more complex strategies of sensorimotor control.Read More......