by Igor SHEVELYOV, Academy Member, Head, Laboratory of Physiology of the Sensory Systems, Institute of Higher Nervous Activity and Neurophysiology, Russian Academy of Sciences
Recognition of visual images is one of the most complex functions of the brain. How and why does it differentiate between the images projected on the retina of the eye? Significant progress in understanding of these operations was made in recent years, though much more things still remain unknown. However, due to new methods of investigation we now can see the contours of a harmonious system of analysis of image signs and their synthesis in a single visual image.
What do we know about the neuronal mechanisms of the object shape perception in different compartments of the visual system? Let us start from the retina of the eye, whose structure and functions are studied most amply; vision is impossible without it. But aren't the previous concepts on its complexity and significance of its functions, linked with visual information processing, and not reception*, exaggerated? Let us take, the traditional assumption "the retina is part of the brain presented at the periphery". Is it so? Comparison of the signal processing and transformation in the retina and in the exterior geniculate body (subcortical visual center),
* Reception is perception of the stimulant's energy by receptors and its transformation into nervous stimulation. - Ed.
In each of the three blocks: upper series: images presented to the cat's eye; lower series: computer-reconstructed relief of neuronal activity in the external geniculate body for charges of 177 neurons.
Scheme of horizontal inhibition (A) and its effect (B).
on the one hand, and in the brain cortex, on the other, demonstrates their obvious difference.
It is well known that transduction (photoenergy transformation into nervous stimulation energy, paralleled by tremendous amplificat ... Read more