Agnosia – All that is gold does not glitter!
Posted on: May 4, 2018.

Hallucination is the perception of things that do not actually exist. It is imagination appearing real—seeing or hearing things that others cannot normally see or hear. Agnosia is the inability to perceive things that really exist. It is real appearing imaginary—not being able to identify or recognize things that others are normally able to perceive.

While hallucination could be a product of poignant psychological shock, agnosia is the result of acquired brain damage. Agnosia however is a less debilitating condition than hallucination; there is an element of fascination in agnosia that cannot be felt in the latter.

Visual agnosia is the most common form among its three major disorder categories: visual, auditory, and somatosensory (tactile) agnosia. Auditory agnosia is the inability to perceive and identify sound, despite intact hearing, cognitive functioning, and linguistic abilities (reading, writing, and speaking). Apperceptive agnosia is a shape perception disorder—an inability to recognize or copy pictures, letters, or even simple geometric shapes—where the brain damage is diffuse, often caused by stroke or carbon monoxide poisoning.

Patients who suffer from visual object agnosia are unable to directly identify objects presented to them visually—such as an empty glass. However, such patients are usually able to “perceive” an empty glass with the assistance of additional cues such as being allowed to hold it or hearing the noise when a spoon is tapped on the side of the glass. This type of disorder is mostly caused by carbon monoxide or mercury poisoning. Particularly in Alzheimer’s Disease, however, lesser degrees of visual object agnosia are commonly encountered, though it may also result from tumours, hypoxic/hypotensive brain damage, or stroke, usually in the posterior cerebral artery territory.

Physical Examination, Neuropsychological Testing—visual distinction between real and unreal objects, facial recognition, verbal and nonverbal sound recognition, odour recognition, and tactile form recognition—and Brain Imaging are used to diagnose a potential case of agnosia. Brain lesions that could potentially result in agnosia can be diagnosed using Magnetic Resonance Imaging (MRI) and Computerized Axial Tomography (CAT) scans. Patients who suffer from agnosia regain sensory function within 4-12 months of diagnosis and can also be given speech therapy and occupational therapy to help cope with their conditions.

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