January 21, 2016
The Oculomotor Sensory System
Dr. Selwyn Super
Vision is regarded as the human being’s dominant sense through which more is directed and learned than from any other sense. It therefore makes sense that of the twelve pairs of cranial nerves, no less than half of these nerves be directly or indirectly concerned with vision.
What the eyes sense and how the eyes move play a vital role in determining what objects we see and where and when we see them. The brain that controls the whole body works in a top down fashion to determine purposes and objectives, and in a bottom up fashion to determine what objects to fixate, and focus on and to combine the images that fall on the retinae of both eyes and fuse them into a single binocular 3D image that can be pinpointed accurately in spacetime.
The giant in ophthalmology, Sir Stewart Duke-Elder who devoted most of his life in writing and editing some 19 volumes about vision and the eyes notes that:
“The most salient factor in the evolution of man was the ousting of smell as the dominant sense and its replacement by the infinitely more useful and effective faculty of vision… To equip the eyes with the power to form the basis of man’s physical dexterity and intellectual supremacy the whole nervous system became reorganized…These changes were dependent upon and were associated with the development of a macula so that exact vision became possible…and with profound changes in the mechanism concerned with moving the eyes which made possible conjugate movements and movements of convergence of such delicacy so as to bring the two images of a single object with precision upon corresponding retinal points.”
Such is the exquisite connection of the human being’s sensory and motor systems that have produced the melodies of life and the impressive advancements in human mental and physical capabilities.
Arnold Gesell who co-authored the book “Vision, its development in infant and child” describes the ‘visual triad’ that relate visual fixation to the human skeletal system, focusing to the human visceral system, and fusing to the human cortical system. An example of the visual triad in operation in layman’s terms would be:
- moving physically to the library and fixating on a specific book, a specific page and specific words;
- focusing on the words in order to see them clearly;
- fusing the images that fall on to the two eyes to see a single binocular image, and at the same time fusing the time-based past knowledge of what you know about the content with what you are now reading and projecting it into the future through memory and to optimize future action.
The brain’s major conduit that combines top down intentions, and bottom up attention is its ocular motor sensory system . How well this performs is dependent on its development and the coordination of literally billions of neural connections, and the intelligent way they are controlled.