|Type of paper:||Research paper|
|Categories:||Biology Anatomy Mental health Psychological disorder|
The neuropsychological disorder basically known as Agnosia refers to the impairment occurring from deriving of the meaning of visually presented stimuli, this is despite the fact the individuals might be having low-level vision, intact sensory and normal language and semantic function. This kind of disorder occurs both scientifically and clinically and researchers have studied that visual agnosis is a method of shading light on how the visual system functions. Visual Agnosia generally refers to the class of neuropsychological disorders upon which the affected person is impaired mainly in deriving the meaning of some or all the categories of the visual stimuli. The term agnosia means "not knowing or "without knowledge" and it captures the failure of recognition that characterizes the general behavior of any person that is having visual agnosia. An example can be given in a situation where a person suffering from Agnosia can fail to recognize the faces of close family members while others fail to recognize day to day objects like the standing lamb. An individual that suffers from visual Agnosia tend to have very intact alertness, language and intelligence setting aside these question about whether the visual Agnosia arises from the reduced elementary visual function or if it arises from the compromised intellectual ability.
Visual Agnosia Overview
The main characteristic of visual Agnosia is the person's inability to access the meaning of various perceptual information that is presented to the visual modernity (Arndt, 2016. This is even though the individual might possess normal language, sensory vision, and intelligence. Significantly, individuals that are suffering from Visual Agnosia generally demonstrate the normal reaction and recognition of various objects through modalities instead of vision and this continues to attest to the fact that the visual agnosia impairment does not come from the difficulties in retrieving names or even in accessing the required semantic function.
This kind of disorder can be general affecting all the kinds of stimuli or it can be specific and this is seen in Agnosia impairment that tends to be very selective, interfering only with the recognition of objects but leaving the recognition of stimuli perfectly intact(Arndt, 2016). Examples of these selective disorders are the prosopagnosia also known as the Agnosia for faces, agnosia alexia described as the agnosia for words and lastly the pure Agnosia that is the Agnosia for the general body parts. The main profile of the Visual Agnosia is that it results from the lesion that is sustained mostly by an adult who has normal premorbid perceptual abilities. However, several reports have been put forth for individuals who have generally become agnostic because of the brain lesion that sustains early in life, a kind of disorder that is mostly referred to as the developmental disorder.
Types of Visual Agnosia
The term visual agnosia was first coined to describe object recognition problems that are observed in some individuals. The apperceptive or the first stage generally constitutes conscious awareness in regards to the sensory impression while the second stage is the associative stage that mainly involves simultaneous concepts that are related to objects (Arndt, 2016). Concerning this two-stage theory, any kind of impairment that might fall in the first stage will mainly result in a perceptive mindblindness a situation where the impaired individual is unable to come up with a good perception representation from the visual point. On the other hand, damage to the second stage would results in the associative mindblindness, a situation where the impaired individual can only derive a reasonably but not an entirely proper description of the input but still cannot apply the well-specified perception to access the stored knowledge of the association and functions of the object (Hamilton, 2016).
Perceptive agnosia said to arise from the breakdown at early stages the visual processing upon which the elementary features of the stimuli are made and the coherent structural description is achieved. Moreover, the individual is not able to copy, identify or even much a drawing that is based on the improvised representation derived from the image. Individuals that fall into these categories are very substantially impaired to represent any kind of incoming visual information.
Individuals that suffer from apperceptive agnosia are unable to construct any kind of stimulus-specific description and the two main types of apperceptive Agnosia are described below:
Visual form Agnosia
Visual form agnosia refers to the class of individuals that have an unclear vision but in their formal examination, they have more than the normal capacity to recognize objects. In addition to this, the individual's ability to recognize colors, brightness, and movement discriminations are preserved, however, their ability to recognize figural properties such as shape, orientation and size are lost (Hamilton, 2016). These kinds of patients don't have the ability to match, copy or discriminate simple visual stimuli and they cannot recognize even simple shapes like rectangles or circles. Individuals in this class of agnosia always do best while using the real image as compared to the line drawings. The performance of these individuals also improves in a situation where a motion accompanied the input because this provides them with additional cues that assist them in shape perception.
Even though some people consider the patients with integrative agnosia not to be too severe as compared to those who are suffering from visual agnosia, others view its distinguishing features to be different from visual agnosia and as a result classifies and recognizes it as an independent entity (Hamilton, 2016). The main feature in this form of agnosia is that the coding of the simple and single case tend to be relatively unimpaired. Significantly, patients that are suffering from integrative agnosia can process the basic features and elements that are present in a display but appear very unable to integrate all the aspect into a whole meaning. These kinds of individuals might perform normally in situations that are related to visual matching tasks and copying but their general perception is compromised. Critically these kinds of individuals perform negatively on tasks that require binding of visual elements in a parallel fashion across visual display type that contains several numbers of stimuli.
For quite a long time, the main type of agnosia has been associative agnosia, a situation where the patients display normal or near-normal performance concerning the tests of perception but they are still impaired at object recognition. In other cases that are associated with associative agnosia, the individual recognition of almost all the objects is abnormal while in other cases the recognition of simple objects such as a pen or even a watch is possible but recognition of complex objects such as mushroom is not very easy. The main causative agent of the associative agnosia is the bilateral infarction of the arteries. This kind of agnosia can be divided into two classes which are impairment in assessing semantics and impairment structural knowledge.
An individual that is suffering from prosopagnosia is not able to recognize individual faces even though they can be able to detect whether a face is present in a particular input. This kind of disorder can be quite severe to a point that an individual might find it difficult to recognize his/her face in a photograph. At the same time, the individual that suffers from this kind of impairment might fail to recognize very close family members. In several instances, these kinds of individuals can be at a position of describing the faces that they are looking at but cannot fully describe a particular person's face. The ability of these patients to extract information that is related to emotional expression is preserved but in other cases, it is impaired. This kind of deficit is mostly perceptual in nature instead of arising from the memory problem or even semantic deficit (Anonymous, & Basu, 2012). Several research and studies have shown that individuals that are suffering from acquired prosopagnosia are always less sensitive to information that relates to the eye as compared to their counterparts. The general idea is that this kind of patient has lost the ability to represent multiple elements relating to individual faces at a perceptual unit and as a result, they rely more on local features for example mouth to identify a person.
Agnosia for Words
This kind of agnosia is also known as the pure alexia or alexia without agraphia. Even though this disorder is always described from the context of language impairment, it is a generally agnostic symptom (Anonymous, & Basu, 2012). This is because individuals that suffer from this disease always show a language impairment that is generally limited to visually presented stimuli. An individual having this kind of disorder might be able to spell a certain word correctly but they end up failing to even read their handwriting. Irrespective of whether this form disease is entirely limited to the word recognition problem or if the other classes of visual recognition are also affected but maybe a lesser degree, the whole scenario remains controversial. The lesion site related to this particular individual is always the left ventral cortex but not always involving the corpus callosum.
Agnosia for Landmarks and Environment
The impairment related to the recognition of landmarks or scenes is generally referred to as topographic agnosia. It can occur with prosopagnosia, or can even occur in isolation. In relation to other forms of agnosia, individuals that are suffering from this kind of agnosia perform quite well in a wide range of memory together with basic perception tasks (Anonymous, & Basu, 2012). However, in topographical cases, known landmarks and buildings tend to lose their familiarity with the patients. Topographic agnosia, however, can be differentiated from the other disorders affecting orientation in a large scale environment.
Several kinds of research have been made in the recent past in a bid to describe and characterize the neuropsychological disorders that are covered by the heading visual agnosia. Even though this kind of disorder is clinical, they give scientists a very unique window in working with the visual system. Visual agnosia and all the related disorders majorly influence the individual ability to recognize an object and this lies in a wide range of recognition. Controlled treatment of the visual agnosia is very rare however patients can demonstrate good improvement under rehabilitation.
Anonymous, & Basu, A. (2012). Visual agnosia. BMJ, 345(nov09 2), e7342-e7342. doi: 10.1136/bmj.e7342
Arndt, G. (2016). Settler agnosia in the field: Indigenous action, functional ignorance, and the origins of ethnographic entrapment. American Ethnologist, 43(3), 465-474. doi: 10.1111/amet.12339
Hamilton, R. (2016). Enhancing diversity in academic neurology: From agnosia to action. Annals Of Neurology, 79(5), 705-708. doi: 10.1002/ana.24635
Misra, H., & Aikat, R. (2016). A Survey of Visual Perceptual Disorders in Typically Developing Children, and Comparison of Motor and Motor-Free Visual Perceptual Training in Such Children. Journal Of Neurological Disorders, 4(6). doi: 10.4172/2329-6895.1000296
Seckington, C. (2006). Book Review: Autism Spectrum Disorders and Visual Impairment: Meeting Students' Learning Needs. Journal Of Visual Impairment & Blindness, 100(6), 377-378. doi: 10.1177/0145482x0610000609
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