Organization and Function of Key Visual Areas - Literature review Example

VISUAL PROCESSING PATHWAY xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx ORGANIZATION AND FUNCTION OF KEY VISUAL AREAS xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx NAME xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx INSTITUTION xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx DATE Description of the Visual Processing Pathway and the Focus on the Organization and Function of Key Visual Areas. Introduction Imaging and histology has over the years continued to evolve and one can have a better understanding of this topic more so in the subject in context which is the visual processingpathway. Various studies have shown that there are twenty or more human cortical visual regions that are not alike. Physiological and anatomical methods have been both established and applied in this research. Narrowing down historically, this visual system is said to comprise of at least two complex sub-systems spatial vision and sub servingobject.The subsequent processing streams have as a result of various studies and experiments been discovered to be organized according to their functions and structure. This study sets out to analyze the various variances and stages of cortical visual areas to bring out a clear understanding of this issue. In this context, we draw together various understanding of how the visual stimuli is delivered and interpreted in the different cortical visual stages. The Visual Cortex Visual cortex is also known as the primary visual cortex or the striate cortex also known as V1. It may also be used define the extra striate visual cortical areas, which are the V1, V2, V3, V4, and V5. The brain is made up of different hemispheres and in each of them, there is a visual cortex. The visual cortex in the left hemisphere detects signals sent from the visual field on the right while signals from the left visual fields are received by the right visual cortex. The Visual Processing Pathway The visual processing pathway is the system or arrangement of stages through which information about objects visualized is transferred. In these stages there is the V1 which is the first and important part of the whole process (Colby 1998). According to various studies, V1 is one of the sensory types found near the calcarine fissure found in the occipital lobe. V1 in all hemispheres detects signals directly from its ipsilateral geniculate nucleus. Information is then transmitted from V1 to the primary pathway. These are the ventral stream and the dorsal streams. The first stage in the dorsal stream is the V1. The second is the visual area V2, goes through dorsomedial area and V5 also known as MT, then to the posterior parietal cortex. Ungeleider and Mishkin also define the dorsal streams as the “where” and “how” pathway as we will later see.This is related mainly on motion, object, location representation, and in the movement of eyes and arms. The ventral stream also referred to as the “what pathway” starts with V1, through V2, goes through V4 and then to the inferior temporal cortex. The stream is responsible for object recognition and representation. It is also the responsible for long term memory and serves as storage for that memory. Fire action potentials are fired by the neurons the visual cortex. This occurs when visual stimuli around their receptive field appears. The receptive field is by definition the area whole visual field that produces an action potential. However, any neuron might respond more effectively to another set of stimuli around its receptive field. This is known as neuronal tuning (Gentillucci et all 1996) Temporal Visual Cortical Areas. As seen earlier, study has shown that the visual system consist of at least two major sub-systems which are functional and structural sub-systems. They are different pathways in the brain and with varying functionality depending on the roles they play in the visual process. There are several cortical stages that develop in the visual pathways. Temporal visual cortex area is divided into a set of stages. As seen earlier, these are the V1, V2, V3, and V4. Further disparity in research and in conceptual theory shows that the visual system can be further differentiated in other sub-systems, one, and recognition of objects of the other for spatial localization. (Greem 1968, pg. 44) There is a classification of the various visual streams in this context. (Ungerleider et al 1982 pg. 102). According to ungerleider and Mishkin the classification is distinct and in their view is classified into two anatomical streams developing from the primary visual cortex (V1). They go further to analyze the classification where a single stream develops ventrally to the infertemporal cortex. On the other hand, the other stream develops dorsally to the posterior parietal cortex. Both systems were developed to explain or rather analyze spatial localization and object discrimination and in their research the two had been termed as “where” and “what” respectively. In the inferior temporal visual cortex areas there is a sub-division, the TE region into a series of sub-areas. There are also various differing areas in the cortex, in the superior temporal sulcus. (Ballylis et al 1987, pg. 150). In the areas discussed last, TPO serve as a receptor for input from the occipital cortex, parietal and temporal cortex. In essence, one of the prime challenges which one must understand and deal with from a visual perspective or rather one that must be tackled by a visual system in regard to objection recognition has to be the degeneration of a representation of what is observed, that enables recognition to be practical or occur and independently relate to angle of view, position on the retina, spatial frequency, contrast and size (Gibson 1979). The Two visual Systems There has been evidence that there are already two visual systems derived from several different sources from the cognition neuroscience research. In this section there is the incorporation of the different sources of the evidence of the two visual system approach, the “what” and the “where”. The two labels “what” and “where” as earlier detailed have been proposed and detailed to indicate object discrimination and spatial localization. In this section we look at the different ways in which the two labels are defined. The cortical distinction evidence for “what” and “where” is developed by Mishkin and Ungerleider and was derived from a lesion study of primates, where stages of visual cortex were developed. This has resulted from recent new developments in physiological studies that have discovered the illusory-contour perception. The study from the primates have led to the conclusion that the stimuli from the illusory-contours are a result of neurons in extrastiate visual cortex V2 as well as those in striate cortex V1. In the human factor, the research study of the human functional magnetic resonance imaging (fMRI) has suggested that illusory-contour stimuli activate multiple cortical areas. Thus showing that they do not only activate V1 and V2 but also those along the visual pathway that is V3, V4. It is therefore important having this findings to embark on a strategy aimed at examining the temporal characteristics as we have earlier seen, in order to bring out clarity of the roles of each area of the multiple illusory-contour study carried out on normal humans may be used to bring out a clear of the subject (Rosa and Tweedale 2002). One carried out on one with normal visual ability suggested that prior rising part of the MEG stimuli may arise from cortical activities common to test and control stimuli which has suggested to be related to local qualities of the stimuli (Ohtani et al 2002) According to Ungerleider and Mishkin approach of “ what “ and “where”, the ventral stream is defined in an almost same manner as that of Ohtani, suggesting that the stream of processing pathways as projecting from V1, V2,V3, and V4. Their study indicates that lesions to the inferior temporal cortex and in this case rhesus monkeys lead to extreme impairment in visual object discrimination functionality. On the hand, they explained the dorsal stream as seen to project from V1, through V2, V3 in middle temporal area(MT), medial temporal area (MST) to the posterior parietal cortex. Brain lesions may bring rise to behavioral deficits in humans and can be specifically defined particularly if the parietal area and the qualities of the spatial impairment. The visual processing pathway stretches therefore along multiple pathways that is the cortical and the subcortical, bringing together a huge portion of the brain structures (Op De Beeck and Vogels 2001). Ablation studies carried out in two different experiments showed that inferior temporal lobe was involved in object discrimination whereas the posterior parietal lobe was involved in spatial localization (Moran and Desimone 1985). Other FMRI studies show that cortical activity has been visualized in response to various types of visual stimuli identified in a single subject. Differentiation in this region of visual activity shown in maps can be seen and analyzed. These maps can be visualized and compared directly to that of the human activity based areas (Hess et al 1989) The research carried out by Goodale and Milner of “what” and “how”, further deviates from the usual dichotomy featuring space and object as perceived since it puts more emphasis on the purpose of the observer or what they set their target as. This theory is persistent of a particular generation-purpose representation of subjects being viewed or space that is not in existence. The study rather defines the visual system as per the roles of output of each stream for a clear and accurate grip scaling. The study has shown that there is a necessity for information about the object, which isthe model of a direct egocentric response. Functions in both streams vary depending on time and also a reference frame (Braddick and O’Brian 2001) In essence, our visual ability varies and more often than not we view things in life as inaccurate. This mostly is evident when sometimes things that we look at appear closer than they really are or when look at tall buildings; they appear to be falling (Baker et al 1991). This however does not necessary affect the accuracy of our behavior. Controlled behavioral studies that are controlled have been analyzed present an important background to the dissociation viewed between phenomenal awareness and visually based action. In this study, time also comes out as important factor (Maunsell and Van Essen 1983). Dissociations between action and awareness are apparent when there is an action in performance without much delay. It is therefore evident that within that within this framework the system that is dependent on the relationship of the observers and the object must necessarily update the egocentric position of the objects (Moyshon et al 1985) Conclusion As a result of the various studies in the cortical visual systems, these details several approaches carried out by different scholarly writers. This paper does not specify or ascertain a particular visual processing pathway, but rather gives an understanding of the various possible processes as earlier studied and also from emerging concepts.This review suggests that one can possibly generalize this distinction even further by the models of reference applied in the spatial tasks. Examining these frameworks helps to distinguish the various visualprocessing stages and also to strike a difference between spatial processing mechanisms. BIBIOGRAPHY Sarah, Dennis R, and profit, 2001, Defining the Cortical Visual Systems: “what”, “where” and “ how. “Department of Psychology.” University of Utah, 380s, 1530 E, Rm 502, Salt Lake City, USA. Ungeleider, and Mishkin,M, 1982, Two Cortical Visual Systems: Analysis of Visual Behavior, MIT Press: Cambridge MA. (pp. 549-586). Baylis, Roll, E, and Leonard, C (1985), Selectivity between Faces in the Responses of a Population of Neurons in the Cortex in the Superior Temporal Sulcus of the Monkey, Brain Res 342,pp. 91-102. Yoshio, O, Shoichi, O, Toshiyuki, S, Akira, A, Yoshi Kazu, Y, Keisuke, T, Yoshimichi, E, 2002, “Magnetic Responses of Human Visual Cortex to Illusory-Contours, Nueroscience Lettters. 321PP.pp. 173-176. Op de Beeck, H, Wagemans, J, and Vogels, R, 2001, Can Neuroimaging really tells us what the Human Brain is doing? The Relevance of the Indirect Measures of Population Activity, Acta Psychologica, 107,pp. 323-351. Maunsell, J, Van Essen, D, 1983, Functional Properties in the Middle Temporal Visual Area of the Macaque monkey, I, Selectivity for Stimulus direction, Speed, and Orientation, JNeurophysiology 49(5):pp. 1127-47. Hess, Baker, and Zihl, 1989, The Motion Blind Patient: Low-level spatial and temporal filters, Journal of Neuroscience 9 (5): pp. 1628-1640. Baker. Hess, Zihl,1991, Residual Motion Perception in a “Motion Blind” patient, assessed with Limited Lifetime Random dot Stimuli.Journal of Neuroscience 11(2): 454-461). Moyshon, J, Adelson, E, Gizzi, M, and Newsome, W.T, 1985, The Analysis of Moving Visual patterns: Pattern recognition Mechanisms (pp.117-151), Rome: Vatican Press. Braddick, J, O’Brian, JMD, 2001, Brain Areas Sensitive to Visual Motion Perception 30 (1): 61-72. Rosa Mg, and Tweedale R, 2002, Visual Areas in Lateral and Ventral Extrastriate cortices of the marmosey monkey, J Comp Neurol422: 621-51. Moran and Desimone, 1985, “Selective Attention Gates Visual Processing in the Extrastriate Cortex,” Science 229(4715). Colby, C, L,(1998), Action-oriented Spatial Reference Frames in Cortex.Neuron,20,15-24. Gentillucci, M, Chieffi, S, Daprati, E, M, C, and Toni, I, 1996, Visual Illusion and Action, Neuropsychologica, 34(5), 369-371. Gibson, J, 1979, The Ecological Approach to Visual Perception, Boston, Houghton Mifflin. Read More