Function of the Visual Nervous System

Sensation

The Visual System is highly complex, yet very systematic and efficient, so much so, that viewing our surroundings comes to us with ease. As a result, very rarely do we stop to think about the initial steps and processes that translate the light around us into the images our brain perceives. This is where sensation comes into play. Sensation is the extraction of visual information, sourcing from the external world. The visual information that our brain receives is comprised of light- different wavelengths and intensities of electromagnetic waves. These wavelengths of light are refracted by the cornea and are projected into the retina. “The resulting retinal image is essentially a pattern of light that changes in intensity and wavelength over space and time” (Albright, 2015).

Retinal Organization (Ask a Biologist, n.d.)

The retina has a receptive field, where the retinal cells are clustered. Retinal cells are of two types, namely rods and cones. Rods are sensitive to light intensity and are used for black-and-white vision. They are located in the periphery of the retina. Cones are less sensitive to light but carry information about color. There are 3 types of cones which respond to different wavelengths of colors in the spectrum.

In this way, our retinal cells almost work like a metal detector. When a person passes through the detector’s frame, some mechanical parts sense the movement of the person walking through and the others detect the metal. There is a similar segregation of function in the retinal cells- the cones are essential for recognizing color, while the rods process shapes and light intensity. Both components work independently of each other but are essential for the completion of the entire task.

Information Transfer

The visual processing system involves three necessary steps to function. Importantly, the information transfer between nerve cells in the body and the brain is essential for producing a connection between what is seen and how it is perceived. The brain is made up of thousands of neurons that efficiently transfer information to and from the visual cortex. Information transfer can be compared to the United States Postal service, where letters and packages are received, sorted, and sent on to their next location, much like sensations are through the body

The mailroom represents a small part of information transfer on a large-scale. Specific letters and packages are taken from one large, collective pool of mail, or, in the brain, information, and distributed throughout the world. (Shore, 2007)

Just like the Postal Service needs to be efficient and timely in the processing of the millions of letters sent every day, the human brain also receives “information from hundreds or thousands of other nerve cells and in turn, transmits information to hundreds or thousands of other cells” (Hubel, 1988). These nerve cells have specific anatomical makeups that, by nature, are meant for the input and output of information. Dendrites are fingerlike fibers branching off the cell body, where the input of information is picked up. The axon then “transmits information from the nerve cell to other nerve cells,” demonstrating the output of information to other cells (Hubel, 1988). This process can be thought of in a similar way as a set of toy trains bumping along a track.

Here is an example of a serial transfer between neurons. The trains subsequently hitting each other and causing movement represents the individual synapses between neurons. (Train on Tracks, n.d.)

The set of toy trains represents a serial transfer between neurons. This means that as one train moves forward, the small knob in the front of the train hits the back of another, sending the energy through to the next train and moving them down the tracks. This compares to the way that nerve cells pass information through synapses. The energy and information are passed along to other nerve cells, like the trains pass their energy on to one another. The processes of information transfer occur in individual neurons in the brain, as well as on a large scale that interconnects thousands of cells to form pathways essential for information transfer and the visual processing system.

Output/Perception

Perception is how individuals understand the world around them, combining the information taken in by sensory organs with high-level visual processing to make sense of images. This involves various parts of the brain, but higher-level processing occurs at the end of the visual stream. One form of high-level visual processing, facial recognition, creates potentially powerful emotional responses, a key to social interactions.

the dress (Bleasdale, 2015)

Kandel explains in The Biology of the Beholder’s Share that “there is a powerful link between the brain’s face detection machinery and the areas that control attention, which may explain why faces in portraits grab our attention so powerfully” (Kandel, 2016). Furthermore, facial recognition allows individuals to perceive others’ emotions based on visual cues, so they can “communicate not only [their] ideas and plans, but also [their] emotions” (Kandel, 2016).

It is important to note that there exist inherent differences between sensation and perception. For example, when an individual is presented with a glass of water, he or she sees the glass and water. However, how one chooses to perceive the amount of water in the glass, as either half full or half empty, is dependent upon one’s emotional attachments. Perception is fundamental to communication yet unique to the individual.

References

Albright T. (2015). “Perceiving.” Daedalus (winter 2015 issue). Cambridge, MA: MIT Press.

Ask a Biologist. (n.d.). Light through the eye [Digital Image]. Retrieved from https://askabiologist.asu.edu/sites/default/files/resources/articles/seecolor/Light-though-eye-big.png

Bleasdale, C. (2015, March 20). The dress [Digital Image]. Retrieved from https://en.wikipedia.org/wiki/File:The_Dress_(viral_phenomenon).png

Hubel, D. H. (1988). Eye, Brain, and Vision. New York: W H Freeman.

Kandel, E. R. (2016). Reductionism in Art and Brain Science. New York: Columbia University Press.

Shore, T. (2007, May 27). Letter processing plant [Digital Image]. Retrieved from https://tinyurl.com/y9k3hd58

Unknown author. (n.d.). Train on tracks [Digital GIF] Retrieved from https://tinyurl.com/ycrvlve3

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