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D M Westine

Publications and source records attributed to D M Westine.

4 recordsLinked to original sources
PubMed1991

The generation of horizontal off-center saccades.

Horizontal saccades are initiated in the lab by a display of nine LEDs spaced five degrees apart and centered with respect to primary position (looking straight ahead). From this setup, there are seventy two combinations of unique saccades. Temporal and spatial information from these recorded saccades are compared to saccades generated from a hypothetical model using the same experiment paradigm. The model uses two neural integrator feedback loops within the premotor circuitry. One is to control the duration of the high frequency burst of neural activity that caused the muscles to contract at saccade velocities and the other to produce the proper neural signal necessary to keep the eye in its new post-saccade position. Depending on the initial position of the eye, different temporal and spatial schemes are necessary to produce the same size saccade. These control strategies are realized by modifying known neural signals within the premotor circuitry.

Humans↗
PubMed1990

Temporal encoding for the control of saccades.

Pre-motor circuitry responsible for the spatial to temporal transformation in the saccadic eye movement system is modelled using gaussian random variables. Eighty percent of the time between stimulus onset and the end of a saccade is spent with the eyes stationary. This time span is when the brain converts the spatial orientation of the visual stimulus into a temporal code for controlling the duration of the high frequency burst of neural activity innervating the eye muscles. This system controls saccades accurately from all different initial positions. Therefore, a ten degree saccade can have durations varying two-fold depending on the eye's initial position in the orbit, and yet the brain centers receiving the visual input are innervated by the same group of neurons for all ten degree saccades. Multiple and double-step stimulus activity is also investigated. This hypothetical model includes neural pathways from the retina, longitudinal geniculate nucleus, superior colliculus, frontal eye fields, striate cortex and the cerebellum.

Brain↗
PubMed1989

Stochastic variables responsible for observed saccadic variability.

A new stochastic local feedback model of the horizontal saccadic system based on time optimal neural control within the superior colliculus has been previously described. This model uses a premotor neural circuit composed of burst, tonic, and pause cells and innervates a fourth order linear homeomorphic muscle plant. A sequence of saccades recorded from human subjects shows great variability in peak velocity, final position, and amount and type of post-saccadic behavior. This variability is duplicated in a sequence of simulated saccades through the use of random variables within the neural circuitry. The random variables are agonist burst cell magnitude, antagonist post inhibitory rebound burst magnitude and timing, and to a lesser extent muscle saturation magnitude. These four random variables are shown to cause all the observed variability in human saccades, including: trajectory profile, velocity profile, dynamic overshoot, and glissadic overshoot and undershoot.

Eye Movements↗