Sensation - absorption of stimuli by the senses and their translation into neurological impulses; Perception - processing of visual data, organization of sensations and comprehension of the sensory input. These two stages, once considered separate processes, are interdependent and recent research demonstrates that perception begins in the
retina
itself.
Sensation is a series of physiological processes which occur in the sense organs in response to stimuli. The stimulus of light activates receptor cells in the
retina
which set off a multi-level process beginning in the physical world and ending with comprehension of the surroundings.
This process occurs along an "optical path" which begins with the eye translating physical properties (i.e. light patterns reflected from the physical surroundings) into neurological impulses, which are routed down the optic nerve to various zones in the brain. These impulses are processed and interpreted, resulting in our perception of the surroundings. Perception and processing of the stimuli include the analysis of shape, size, distance, color, space and movement.
Eye and Brain, Leonardo Da Vinci, c. 1500
Finally, this data is interpreted and made coherent in the brain - what has been seen is recognized and comprehended. The visual path is comprised of a number of stages. Nonetheless the process of seeing is not a continuum; some processes take place concurrently, are intertwined or include feedback loops. The stages are:
•
The physical world - transmitted to the eye by light waves (stimuli).
•
The eye - reception of the stimuli, initial processing and translation into neurological impulses.
•
The optic nerve -
transmission
of impulses to the brain and concurrent processing of specific data.
•
The brain - the comprehension mechanism which registers and interprets the data.
The visual path is demonstrated by sightlines leading from the object through the eye and along the optic nerve to the primary visual cortex in the brain.
Although
visual perception
is a basic process common to all human beings, the subjective nature of the process accounts for certain differences between one person and another, one nation and another, and one culture and another.
For example, the Bible in Hebrew, which is perfectly intelligible to an Israeli, seems a meaningless succession of lines and dots to someone who doesn't know Hebrew.
