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Biomedical subjects

L Stark

Publications and source records attributed to L Stark.

At least 145 records · Page 8Linked to original sources
PubMed1975

Computer simulation of overshoot in saccadic eye movements.

The human horizontal eye movement system produces quick, precise, conjugate eye movements called saccades. These are important in normal vision. For example, reading tasks exclusively utilize saccadic eye movements. The majority of saccades have dynamic overshoot. The amplitude of this overshoot is independent of saccadic amplitude, and is such that it places the image of the stimulus within the retinal region of maximum acuity within a minimum of time. A computer based model of the saccadic mechanisms was used to study the origin of this overshoot. It was discussed that dynamic overshoot cannot be attributed to biomechanism properites of the eye movement mechanism, but must instead be explained by variations in the controlling nervous activity. The form of this neural controller signal is very similar to that required for a time optimal response of an inertial system.

Computers↗
PubMed1975

Integral control in accommodation.

Models of the accommodation system available inthe literature may be classified as proportional controller, optimal bang-bang controller and pure integral controller types. Each of these models explains only some aspects of the experimental behavior of the system and conflicts with other experimental observations. Based on two different experiments in which the built-in phyiological feedback loop has been opened, a leaky-integrator element is proposed for the accommodation controller. This element appears to resolve the conflict between the proportional and integral controller models and also explains the experimental observations better than any of the existing models.

Accommodation, Ocular↗
PubMed1975

Descartes' law of reciprocal innervation.

Reciprocal innervation plays a crucial role in the fine motor control exhibited in body movements and this is especially true for the precise ocular rotations demanded of the extrinsic muscles of the eye. Although Galen, in 157 AD, was knowledgeable in human anatomy and muscle function, it was Descarted, who in 1626 first conceived of model for the nervous system controller, of a muscular mechanism for movement of the extra-ocular plant, and of reciprocal innervation as the linking principle to provide for control of agonist and antagonist muscles. Bell, in 1826, and Sherrington in 1893, clearly demonstrated reciprocal innervation in their experimental animals. Additional qualitative neurophysiological evidence supporting the concept of reciprocal innervation has been provided by clinical case reports, by electromyographic recording from the extraocular muscles, and by monitoring single unit activity in the extraocular motor nuclei. Recently the applicatio of bioengineering concepts, such as time optimal control and quantitative models to elucidate the nature of the neural signals sent by the brain to command eye movements have further emphasized the importance of Descartes' "Law of Reciprocal Innervation."

Animals↗
PubMed1975

Closely spaced saccades.

The relationships between saccadic velocity, duration, and magnitude have been used to prove the normalcy of saccades with intersaccadic intervals of less than 200 ms. Pairs of normal saccades with small intersaccadic intervals will have the second saccade larger or smaller and going in the same or the opposite direction than the first saccade. These normal saccades may be horizontal, vertical, or oblique.

Electrooculography↗