Human Visual Perception Is Achieved by a Single Area of the Brain - Essay Example

The brain and not the eye is the true organ of visual perception since the resolution of computational problems is achieved by the brain (Cook, n.d To be able to know where the mistakes in the idea that the human visual perception is achieved by a single area of the brain that simply reflects the visual information coming from the eyes lie, we have to understand different concepts under visual pathways, primary visual cortex, multiple parallel pathways and the problem of visual unity. After nerve impulses leave the retinas, they pass backward through the optic nerves which consist of about a million nerve fibers and contain axons arising from the inner, ganglion-cell layer of the retina (Guyton & Hall, 1996; Waxman, 2000). The arrangement at the optic chiasm allows the left hemisphere to receive visual information about the contralateral half of the visual world and vice-versa (Guyton & Hall, 1996; Waxman, 2000). Moreover, the fibers of each optic tract synapse in the dorsal lateral geniculate nucleus and from here, the geniculocalcarine fibers pass by way of the optic radiation to the primary visual cortex in the calcarine area of the occipital lobe (Guyton & Hall, 1996). The most important cortical region for visual processing is Area V1 in the occipital lobe because it is the first stop in the cortex and almost all of the signals that the other cortical regions get must pass through it which is why Area V1 is often referred to as the primary visual cortex or striate cortex (Coren, Ward, & Enns, 1999). Hubel and Wiesel found cells in the cortex with receptive fields that have excitatory and inhibitory areas and are arranged side-by-side rather than in a center-surround configuration (Goldstein, 2007). Simple cortical cells are cells which have these side-by-side receptive fields mentioned previously and these cells respond best to bars of a particular orientation (Goldstein, 2007). Other kinds of cells in Area V1 are even tuned to more complicated pattern properties of the stimulus such as complex cortical cells which respond best to movement of a correctly oriented bar across the receptive field, and at an even more complicated level of analysis than the complex cells are hypercomplex or end-stopped cortical cells that respond not only to the orientation and direction of movement of the stimulus but also to the length, width, or other features of shapes, such as the presence of corners (Coren, Ward, & Enns, 1999; Goldstein, 2007). Simple, complex, and hypercomplex cells are referred to as feature detectors since they fire in response to specific features of the stimulus such as orientation or direction of movement (Goldstein, 2007). The cortex is also organized into columns. The cortex is “organized into location columns that are perpendicular to the surface of the cortex and that the neurons within a location column have their receptive fields at the same location on the retina” (Goldstein, 2007, p. 75). Moreover, the cortex is also organized into orientation columns as well as ocular dominance columns (Goldstein, 2007). In addition to V1, there are also other visual areas in the occipital lobe of the cortex which are sometimes called as prestriate cortex or extrastriate cortex (Coren, Ward, & Enns, 1999). Area V1 does not actually carry the same type of information to these other cortical maps, rather it segregates three major types of visual information namely form, color, and motion and sends these information to separate cortical regions for processing (Coren, Ward, & Enns, 1999). The other visual areas are the following: V2 which represents visual information in similar ways as V1, V3 which is a visual map for form and local movement, V4 which is a visual map for color, and V5 which a visual map for global motion (Coren, Ward, & Enns, 1999). At this point, it is also important to note that even if the occipital lobe is considered as the primary visual receiving area, other lobes of the brain also play a role in visual processing. There is a pathway leading to the temporal lobe which is also known as the ventral or what pathway and there is also a pathway leading to the parietal lobe, known as the dorsal or where pathway (Goldstein, 2007). Furthermore, the IT or inferotemporal cortex has something to do with form perception while the MT or medial temporal cortex has something to do with motion perception (Goldstein, 2007). From all of the things mentioned here, we can readily see where the mistakes in the idea that human visual perception is achieved by a single area of the brain that simply reflects the visual information coming from the eyes lie. First, even though there is a “primary visual cortex,” human visual perception is still not achieved by a “single” area of the brain. There are different channels for form, motion, and color information and there are also specialized cortical maps for the representation of the information but what we really have to take note of is that these channels and maps must interact and communicate with one another to produce the various aspects of our visual experience (Coren, Ward, & Enns, 1999). The phrase interact and communicate with one another in the previous sentence suggests that a single area of the brain is not sufficient on its own to carry out a task as complex as visual perception. Moreover, the different maps that can be found in the cortex are operating in the same time or in parallel. Another mistake in the idea that human visual perception is achieved by a single area of the brain that simply reflects the visual information coming from the eyes is that the visual system does not simply reflect the visual information coming from the eyes. We wouldn’t need the specialization of function of areas as well as the many different maps of the visual field if the visual system has a simple function of reflecting the visual information coming from the eyes. According to Coren, Ward, and Enns (1999), the function of the visual system is not to re-create an image of the outside world in the brain, because its function is to recognize objects, to locate them in space and to assist individuals to respond properly to objects and events around them. Moreover, according to Pinel (2006), “the visual system does not passively provide images of the external world; it actively extracts some features of the external visual world and from these it creates visual perceptions” (p. 153). References Cook, R.G. (n.d.). Visual perception. Retrieved November 22, 2008, from http://www.pigeon.psy.tufts.edu/ecp.htm Coren, S., Ward, L.M., & Enns, J.T. (1999). Sensation and Perception. (5th edition). San Diego: Harcourt Brace College Publishers Goldstein, E. B. (2007). Sensation & Perception. (7th edition). Belmont, CA: Thomson Wadsworth. Guyton, A. C. & Hall, J. E. (1996). Textbook of Medical Physiology. (9th edition). Philadelphia, Pennsylvania: W.B. Saunders Company. Pinel, J. P. J. (2006). Biopsychology. (6th edition). Boston: Pearson Education, Inc. Waxman, S.G. (2000). Correlative Neuroanatomy. (24th edition). New York: McGraw-Hill Companies, Inc. Read More