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visual agnosia essay (neuropsychology, 4th year undergraduate)
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An essay I wrote for neuropsychology about visual agnosia for anyone who is looking for an example or needs some inspiration.
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Module Assessment – CoversheetModule Name: Applications of Neuropsychology and Cognition
Module Code: PSYC10022
Assessment Title (Word Length): Essay (2000 words)
Word Length for your submission: 2162 words
Submission Date: 18/10/2019
, Visual agnosia and the complexity of visual perception
In everyday life, the ability to identify and categorise objects is a cognitive ability that
is taken for granted and implemented facilely and promptly. However, in some cases, this
essential aptitude is impaired even though the senses are unaffected. Agnosia is a rare
disorder whereby a patient is incapable of recognising and identifying objects, persons, or
sounds using one or more of their senses that is not associated with a deficit in general
intelligence. The capability of perceiving objects is never abolished completely; it is usually
restricted to specific sensory systems without affecting others. A patient with visual agnosia
is unable to recognise an object visually but can recognise it tactilely or auditorily (Goldberg,
1990). The human visual system is composed of two distinct pathways in the brain
originating from the visual cortex. The ventral stream is involved with object recognition.
The dorsal stream is involved with processing an object's spatial location (Goodale & Milner,
1992). Visual agnosia was first defined by Lissauer in 1890. He described two types of visual
agnosia, namely “apperceptive visual agnosia” and “associative visual agnosia”.
Apperceptive visual agnosia is a disorder of intricate visual perceptual processing.
Individuals cannot fully perceive what they are seeing due to difficulties in perceptual
grouping processes; the patients are thus unable to organise individual segments and edges to
form a whole picture of what they are seeing (Grossman, Galetta, Ding, Morrison,
D’Esposito, Robinson et al., 1996). Although patients with apperceptive visual agnosia do not
acquire brain damage in precisely the same area, damage in proximity to the occipital lobe is
fundamentally correlated with the symptoms of deficit seen in apperceptive visual agnosia
(Grossman, Galetta & D'Esposito, 1997; Shelton, Bowers, Duara & Heilman, 1994; Sparr,
2000). Associative visual agnosia occurs even though perception is normal. However,
individuals have a visual access impairment to semantic representations in order to recognise
the object that they are seeing (Fery & Morais, 2003). Associative visual agnosia is usually
, ascribed to infarction of the left occipital and temporal lobes. This is due to damage to the
ventral stream which leads to the inferior temporal lobe and is crucial for object recognition
(Goldberg, 1990; McCarthy & Warrington, 1986). Two case studies of visual agnosia will
now be examined to demonstrate how research regarding these conditions has contributed to
the understanding of visual perception, category specificity and the internal representation of
reality.
The first case study examines a 29-year old man referred to as MD, who experiences
associative visual agnosia. MD is well within the normal range of intelligence, with no
indication of intellectual decline. The patient’s immense deficits are in visual object
recognition, particularly of animals and faces. Jankowiak, Kinsbourne, Shalev and Bachman
(1992) investigated MD’s visual access to semantic knowledge of objects in a few different
ways. They tested his ability to classify functionally related objects, distinguish between
pictures of real objects and pseudo objects, and draw familiar objects from memory.
The first test was of MD’s ability to detect and classify patterned visual stimuli. MD
was shown 28 black and white drawings; these were of the category’s furniture,
transportation and animals. Pictures were shown first for 100 milliseconds and then for 1,000
milliseconds. After each show, he was asked to copy the pictures. He was able to draw the
objects he had been shown, although when asked to identify them, he was at times unable to
recognise what he had drawn. His ability to draw pictures he had been shown signifies
preserved visual pattern perception.
The next test examined his ability to copy stimuli. Nine pictures of animals were
shown; MD was asked to draw each one and to state, before and after finishing the drawing,
what he thought the picture was. MD was able to correctly identify only 1 out of the 9
samples, though he was conscious that all were animals. He was able to accurately describe
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