hologram that is not among the stored patterns, multiple reference beams -- and therefore multiple focused spots, are the result. The brightness of each spot is proportional to the degree of similarity between the input image and each of the stored patterns. In other words, the array of spots [weights in a layer of a PDP network] is an encoding of the input image, in terms of its similarity with the stored database of images. ( Psaltis & Mok, 1995, p. 76.)
Putting this together with the McNaughton's data showing that the hippocampus represents the path taken by an animal down an alley maze, encoding in the hippocampus may be both holographic-like and patterned in space and time. The hypothesis is that as multiple paths become represented in the hippocampal formation, a transformation into holographic-like surface distribution in the spectral domain is effected. When subsequently a particular path is sought, the buffer operates much as does the holographic memory described above. Initially, actual paths construct the holographic memory and during retrieval, scan paths activate the comparator to access a particularly appropriate actual path. Essentially, the process implements a shift in coordinates from space-time (configurational) to spectral and back to configurational.
The shift of coordinates is suggested to take place by way of scanning, that is, constructing a particular scan path. Computational models such as those proposed by Harth, Unnikrishnan and Pandya ( 1987) and by Yasue, Jibu and Pribram ( Pribram, 1991) have been developed for vision to account for the selection of coordinates as a result of internal scanning. The shift from spectral to the configuration coordinates has been demonstrated in the visual system both at the thalamic and cortical level. Electrical stimulation of temporal or frontal lobe cortex enhances or diminishes the extent of the inhibitory surrounds and flanks of dendritic receptive fields in thalamus and cortex so that the sensory channels can either become multiplexed or fused. As the dendritic fields can be described in terms of a space-time constraint on a sinusoid -- such as the Gabor elementary function, the constraint is embodied in the inhibitory surround of the field. Enhancing the surround enhances processing in configuration coordinates; diminishing the surround enhances the sinusoidal (spectral domain) aspects of processing. Thus, the development of scanpaths operates on the inhibitory process that characterize the fluctuations of the polarizations of the dendritic connection web.
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