The Human Retin The Two Levels Of Visual Processing

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The human retina contains two basically different types of photoreceptors that function independently of each other and operate under different conditions. This phenomenon is called the duplicity theory. The duplicity theory states that we have two different systems of vision, one that is mediated by the rods and one that is mediated by the cones. They serve two separate visual functions. Rods function to facilitate night vision and peripheral vision. They have relatively poor ability to distinguish detail, motion and are insensitive to color. Rod vision also has high convergence, meaning many photoreceptors synapse onto one neuron. Cones facilitate day vision, provide more detailed visual resolution, motion detection and color vision. Cone vision also has low receptor/neuron convergence, meaning one or a few photoreceptors …show more content…

Learning about the anatomy of each stage of visual processing helps us understand how we see. When learning about visual processing, we recognize that there are two different systems of visual perception, one that is mediated by our cones and one that is mediated by our rods. The rods and cones are seen at each level of visual processing; without them we would not be able to see. The chemicals within these cells are broken down by light. Very low light levels will break down the rhodopsin in the rods, and high light levels will break down opsins in the cones. When these visual pigments are broken down, a signal is generate that is transmitted to the visual centers in the brain. The duplicity theory of vision concerns the comparisons and interaction between the rod and cone systems in the visual pathways. It helps explain why we have both rods and cones because a single receptor cell cannot produce both high light sensitivity and high resolution. This helps us understand why we are able to see during the day (cone system) and why we are able to see at night (rod