Recent analyses of the human visual system have surfaced new and exciting information about the operation of the perigeniculate nucleus (PGN). The PGN is a component of the thalamic reticular nucleus that is in turn a component of the thalamus of the midbrain. The PGN is a major feature extraction engine of the human visual system.
The perigeniculate nucleus operates in conjunction with the pulvinar as the PGN/pulvinar couple. This couple is the physiological analog of the conceptual cyclopean retina of Julesz. It is also the couple responsible for the ability of the human to read.
The PGN is a major component of the Precision Optical System, a group of neurological elements controlling the pointing, accommodation and aperture control functions related to vision. These elements include;
1. The photoreceptors found in the foveola, the highest performance portion of the fovea of each eye.
2. The perigeniculate nucleus
3. The pulvinar
4. The oculomotor nuclei (the neurons controlling the muscles of the eyes).
5. The oculomotor muscles
6. The thalamic reticular nucleus (that is the control center for all visual (and many other sensory functions)
It is now possible to specify, in detail, many of the major functional routines performed by the PGN in closed mathematical form. First, it is useful to describe the major functional routines performed by the POS. These functions include;
1. The version routine that points the two eyes in a particular direction.
2. The vergence routine that converges the two eyes at a particular distance.
3. The accommodation routine that focuses the eyes at the desired distance.
4. The light control routine that closes the iris when appropriate.
5. The overall analytical routine that leads to the analysis of fine detail and to reading.
Within the POS, the perigeniculate nucleus is responsible for extracting the information from the signals, roughly 23,000, received from the photoreceptors in each foveola of each eye. To perform this function, the PGN is organized as a two-dimensional, multi-plane associative correlator. In this configuration, the PGN is able to accept the slightly different images of an object in its field of view and perform multiple functions. It can;
1. Under the proper conditions, fuse the two images into one three-dimensional mathematical representation of the original scene. A process of global stereopsis.
3. Extract any error between the centroid of the desired scene (in x,y coordinates) and the point of fixation of the eyes.
4. Use the above global version error to cause the POS to repoint the eyes.
5. Extract any error between the centroid of the desired scene (in the z-axis) and the point of fixation of the eyes.
6. Use the above global vergence error to cause the POS to reconverge the eyes.
7. In the absence of other information, the POS will use the above vergence error to calculate a new focus condition (accommodation) as well.
8. extract the mean location (in x,y & z coordinates)of each significant edge in the original scene presented to the foveola of step 1.
9. Present the above group of x,y & z coordinates in a feature map (called an interp map) to the pulvinar for further analysis.
The other half of the PGN/pulvinar couple, the pulvinar has many of its own functions to perform. Two of the most important involve the perception of individual elements of the scene presented to the foveola. This perception process involves two relatively distinct functions;
1. The extraction and identification of complex but abstract geometric shapes.
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