Anoxic Visual System

Visual agnosia refers to the “…inability to recognize objects that results neither from general intellectual loss nor from a loss of basic sensory abilities,” (Anderson, 2009, p. 32). There are generally two types of visual agnosia: apperceptive agnosia and associative agnosia. Apperceptive agnosia is the inability to recognize or draw simple shapes as they are shown or represented. Associative agnosia is the ability to recognize and copy drawings of simple and complex shapes. However, person with associative agnosia are unable to recognize the complex objects (Anderson, 2009).

Throughout history, a human being was always reliant on the primary sensory areas. An ability to communicate and contract languages is considered to be a unique ability of human nation as no other species show an equal amount of complexity in terms of the structure and sound combination. On the other hand, primary visual cortex provides a skill set in order to identify the objects presented in the world, the distance towards them as well as to design a set of actions in order to incorporate some items such as a stone or a pen. The understanding of these systems is crucial, especially for those who suffer from strokes and tumors and as a result lost the ability to visually recognize objects or hear other people. This work will focus of the structure

Prosopagnosia, also called face blindness, is a neuropsychological condition that refers to impairment in the recognition of faces. Although prosopagnosic patients suffer from other types of recognition impairments (place recognition, car recognition, facial expression of emotion, est.), they experience face recognition problems above or over other types impairments. Prosopagnosia occurs without intellectual, sensory or cognitive impairments; in other words, people with prosopagnosia can still recognize people from non-facial cues. They cannot recognize familiar people by their faces alone, and often use alternative routes to alleviate the effects of this impairment. These routes include

Two brain structures that could likely be affected by this damage are the frontal lobes and the temporal lobes. The frontal lobe produces speech, controls motor skills, and initiates leading functions such as thinking, personality, emotion and memory. (Huffman, K., Dowdell, K. 2015. Pg. 71). The temporal makes it possible for an individual to hear properly, comprehend language, recollect thoughts, and maintain emotional stability; this lobe also contains the auditory complex, which is responsible for the interpretation

A medical definition of vision impairment is a sine qua non that prohibits 20/20 vision in one or both eyes (Bowman, Bowman, Dutton & Royal National Institute for the Blind, 2001; Vision Australia, 2015; Webster & Roe, 1998). Examples of vision impairment include, cataracts, which has the lens inside the eye increasingly cloudy; albinism, which is passed down genetically affecting clear vision and causes sensitivity to bright light; optic nerve damage, which affects field of vision as those nerves controlling vision are disrupted; macular degeneration, where parts of the retina that control colour and fine details are affected; retinitis pigmentosa, which is an ongoing reduction of the field of vision available and nystagmus, where the eye flickers involuntary (Bowman, Bowman, Dutton & Royal National Institute for the Blind, 2001; American Foundation for the Blind, 2015; Vision Australia, 2015 ; Baton Rouge Regional Eye Bank, 2015). John suffers from retinitis

During their 20-year collaboration, Dr. Wiesel and Dr. Hubel also showed that sensory deprivation early in life can permanently alter the brain’s ability to process images, causing vision impairments. Their work was the first to demonstrate the existence of a “critical period” during which the brain must develop crucial connections to the eye.

In this study, experimenters selectively lesioned layers 1-2 (M pathway) and 3-6 (P pathway), then mapped out the corresponding visual field area that suffered the lesions. They found that lesions of the P geniculate layers generated severe impairments in contrast sensitivity and stereoscopic vision at high spatial frequencies, as well as color, texture, pattern, and one of the shape discrimination tasks (Fig x). Lesion to M layers, on the other hand, produced impairment in flicker detection and the two motion detection tasks they studied. Interestingly, they noticed that neither M or P lesions alone led to significant impairment in brightness discrimination, or in coarse shape discrimination. These findings imply that M pathway seems sufficient to preserve some shape discrimination, and challenges the view that P pathway is the sole input for extrastriatal form

It occurs frequently in stroke and traumatic brain injuries due to the way vision is represented in the brain. The visual images that we see to the right travel from both eyes to the left side of the brain, while the visual images we see to the left in each eye travel to the right side of the brain. Therefore, damage to the right side of the posterior portion of the brain can cause a loss of the left field of view in both eyes. Likewise, damage to the left posterior part of the brain can cause a loss of the right field of vision. The most common causes of this damage include stroke, brain tumor and trauma. (What is hemianopia? UCL, Eye search therapy, institution of

Early research by Hubel and Wiesel (1959) on the visual system of cats and kittens suggested that the adult visual system is unable to ‘recover’ after damage. They propose a critical period for normal nervous system developed, during the first few months of life, in which the brain is still able to change, after which the brain was hard-wired (Hubel & Wiesel, 1959).

Diffuse axonal injury occurs in nearly half of all severe craniocerebral traumas. Lesions in the white matter over a wide area of the brain, often affecting the brainstem, corpus callosum, and cerebral hemispheres are caused by DAI. Studies show that DAI is a result of traumatic acceleration/deceleration, and ninety percent of patients with severe DAI never regain consciousness, while those who do survive often face significant impairs. This injury is extensive and is considered diffuse rather than focal because it occurs over a widespread area of the brain rather than one specific location of the brain.

The Magnocellular pathway carries information from the M ganglion cells at rapid speed along the dorsal stream to the parietal lobe to help us understand motion, spatial relationships and contrast. The Parvocellular pathway carries information from the P ganglion cells at slower speed along the ventral stream to the temporal lobe to help us process fine details of such as color and form of an object. It is thought that the Parvocellular pathway is our primary source for recognition and identification, but there are speculations that its allocentric frame of reference can also be used in a more egocentric approach (i.e., the Parvocellular pathway is able to elicit an autonomic response like the Magnocellular pathway). This research expands on these theories by studying the role of color vision in autonomic attention responses. The experiment attempts to study the relationship between the Magnocellular pathway and Parvocellular pathway through color cues and its effects in capturing attention and control visual behavior (e.g., moving the eyes to locate the

In 2002, Slotnick et al. (2002) determine the retinotopic organization of a patient with congenital dysgenesis and normal visual function. The subject was a 32 year old left handed woman with hemispheric cerebral dysgenesis. She underwent a partial right lobectomy at age 30 for treatment of medically intractable seizes. Detailed perimetry mapping within the central 60º of the visual field revealed normal visual function. The findings show that the retinotopic map of the upper right visual field on the ventral left hemisphere was largely normal in both location and organization, but the retinotopic map of the lower right visual field on the dorsal left hemisphere was shifted in location relative to normal. The most focal aspect of the patient’s

Achromatopsia is a non-progressive and hereditary visual disorder which is characterized by decreased vision, light sensitivity, and the absence of color vision. In the U.S., it affects about 1 in every 33,000 people. “Achromatopsia is sometimes called ‘Day Blindness’, as these people see better in subdued light. People with complete Achromatopsia will have reduced vision (20/200 or less) due to an abnormality of the retina. They also have no color vision, sensitivity to light (photophobia) and the presence of nystagmus (shaking of the eyes). People with incomplete or partial Achromatopsia may have

Agnosia is defined as the inability to recognize objects through the processing of sensory information, which means there is no deficit in semantic memory or problems with naming objects. An individual suffering from agnosia still possesses all the relevant semantic information tied to a precept, but they cannot recognize the precept when it is presented to them and therefore trigger the recall of said information. There are many types of agnosia, but this essay will focus on visual object agnosia and prosopagnosia. The former is the inability to recognise objects: patients suffering from visual object agnosia do not have impaired vision, and in some cases can even copy the object they are seeing (patient H.J.A., Humphreys & Riddoch, 1987) or draw it from memory (patient D.F., Milner & Goodale, 1992), but are unable to recognize it when they see it. In the latter, prosopagnosia, patients cannot recognise faces of familiar individuals, and have to rely on other characteristics such as their voice or clothing to recognize them. Patients suffering from prosopagnosia can either acquire it through a lesion in relevant brain areas (acquired prosopagnosia) or for less understood reasons have it from birth, in which case it is termed developmental prosopagnosia. The study of patients with agnosia is integral to the field of visual recognition, as the specifics of their deficits can provide great insight into the ways our brain processes information; for example, the location of

Occipital lobe is the portion of central nervous system, accountable for deciphering vision. Thus, any impairment to optic nerve can sternly affect central vision, peripheral vision and color vision of an individual. The functional aberration in any of the above major constituents might cause serious eye glitches; which if overlooked, might gradually result in vision loss. Thus, there are a number of eye conditions such as retinopathy or some forms of corneal sicknesses, which can be very upsetting for some of the patients; where as some of the other disorders can be so subtle that they can be routinely treated by an ophthalmologist.