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Models

(see also: FDM-project)

3-loop model

The generation of a visually guided saccadic eye movement is a very complex operation of the brain. There are 3 main pathways stem connecting the retina of the eye with the efferent eye movement generating system (EM):
  • first loop: retina - striate visual cortex(V1) - superior colliculus - EM
  • second loop: retina - V1 - prestriate visual cortex - frontal eye field - EM
  • third loop: retina - V1 - prestriate visual cortex - parietal cortex - frontal eye field.

Express saccades (80 ms - 120 ms in man) are generated according to the first loop, fast regular saccades (140 ms - 170 ms in man) according to the second loop, and slow regular saccades (180 ms - 250 ms in man) according to the third loop.

literature:

  • Fischer, B.: The preparation of visually guided saccades
    Reviews in Physiology, Biochem. and Pharmacol., (1987) 106:1-35
  • Fischer, B. and Boch, R.: Cerebral Cortex.
    In: R. Carpenter (ed.): Eye Movements, Vol. 8: Vision and Visual Dysfunction.
  • Fischer, B. and Weber, H.: Express saccades and visual attention
    Behavioral and Brain Sciences, (1993) 16:553-610

neural network implemention

A neural network, consisting of 4 modules with 16 artificial but realistic neurons was build in order to make computer simulations of the 3-loop model. Two transient-sustained input lines drive the network, the impulses are poisson distributed. The model works completely deterministically; its stochastic output is a consequence of the stochastic properties of the input only. Simulations show how multimodal distributions of saccadic reaction time are produced as a natural consequence of the model structure. The gap effect on saccadic reaction times is correctly produced by the model.

literature:
Fischer, B. and Gezeck, S. and Huber, W.:
The three-loop model: a neural network for the generation of saccadic reaction times
Biol.Cybern. (1995) 72: 185-196
abstract

Detecting multimodality by a statistical methods

The excess mass test was used to analyse about 1000 data sets (of about 100 saccadic reaction times each) in order to detect the number and the position of different peaks. With a simulation study the conservative behaviour of this test was shown. Yet, the mean of number of peaks in all distribution is nearly two. The distribution of the the position of all peaks exhibits the express mode, the fast, and the slow regular modes.


Author: Dr. Stefan Gezeck
back to Express Saccade Laboratory

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