PSY 2C 08: BRAIN, BODY AND
BEHAVIOUR
UNIT–I: BRAIN AND BEHAVIOUR
TOPIC: AGNOSIA
, AGNOSIA
Agnosia is a perceptual disorder in which sensation is preserved but the ability to recognize a
stimulus or knowing it’s meaning is lost. Agnosia means “with out knowledge”. patients with
agnosia cannot understand and recognize what they see, hear, or feel. Agnosia result from
lesions that disconnect and isolate visual, auditory and somatosensory input from higher level
processing. Perceptual skills have a hierarchical and parallel organization. The nature and
severity of perceptual impairment depends upon modality affected and the level at which
sensory processing has been interrupted. It is rare in its in it’s pure form. Less than one
percent of all neurological patients have agnosia. When assessing agnosia, it is important to
establish that sensation is preserved; the patients is alert, intelligence is intact (or near intact)
with no language or memory disorder. Examination involves assessing what the patient sees,
hears or feels when presented with objects, pictures or sounds using a combination of clinical
procedures and neuropsychological tests.
The history of agnosia contains several striking examples of the interplay between cognitive
theory and clinical practice, and represent a good example of how scientific advancement is
not always linear or cumulative. There has been a recent revolution in the field of agnosia as
we have more primarily from an almost exclusive emphasizes on disconnection concept to a
more cognitive neuropsychological perspective. Because models of normal perception have
always driven conceptualization of agnosia, brief review of four broad models will be
provided before discussing the major agnostic syndrome.
1. STAGE MODEL
The earliest neuropsychological idea of the process of object recognition were embodied in
“stage models” which held that the cortex first built up a percept from elementary sensory
impressions. Lissauser (1890) argued that recognition proceeds in two stages : apperception
(he meant that the conscious perception of sensory impression; the construction of a separate
visual attribute in to whole) and association ( the imparting of meaning to content of
perception by matching and linking in to a previous experience). A central idea that object or
face recognition depends not just an integrity of early perceptual process but also on later,
culminating “gnostic” stage in which the visual impressions are combained in such a way as
to assess a internal representation.
2. DISCONNECTION MODEL
In 1965 Geschwind’s view agnosia resulted from a disconnection between visual and verbal
processes. He cited anatomic evidence from the syndrome visual object agnosia, which in his
view was most often seen in the context of left mesial occipital lobe damage. According to
BEHAVIOUR
UNIT–I: BRAIN AND BEHAVIOUR
TOPIC: AGNOSIA
, AGNOSIA
Agnosia is a perceptual disorder in which sensation is preserved but the ability to recognize a
stimulus or knowing it’s meaning is lost. Agnosia means “with out knowledge”. patients with
agnosia cannot understand and recognize what they see, hear, or feel. Agnosia result from
lesions that disconnect and isolate visual, auditory and somatosensory input from higher level
processing. Perceptual skills have a hierarchical and parallel organization. The nature and
severity of perceptual impairment depends upon modality affected and the level at which
sensory processing has been interrupted. It is rare in its in it’s pure form. Less than one
percent of all neurological patients have agnosia. When assessing agnosia, it is important to
establish that sensation is preserved; the patients is alert, intelligence is intact (or near intact)
with no language or memory disorder. Examination involves assessing what the patient sees,
hears or feels when presented with objects, pictures or sounds using a combination of clinical
procedures and neuropsychological tests.
The history of agnosia contains several striking examples of the interplay between cognitive
theory and clinical practice, and represent a good example of how scientific advancement is
not always linear or cumulative. There has been a recent revolution in the field of agnosia as
we have more primarily from an almost exclusive emphasizes on disconnection concept to a
more cognitive neuropsychological perspective. Because models of normal perception have
always driven conceptualization of agnosia, brief review of four broad models will be
provided before discussing the major agnostic syndrome.
1. STAGE MODEL
The earliest neuropsychological idea of the process of object recognition were embodied in
“stage models” which held that the cortex first built up a percept from elementary sensory
impressions. Lissauser (1890) argued that recognition proceeds in two stages : apperception
(he meant that the conscious perception of sensory impression; the construction of a separate
visual attribute in to whole) and association ( the imparting of meaning to content of
perception by matching and linking in to a previous experience). A central idea that object or
face recognition depends not just an integrity of early perceptual process but also on later,
culminating “gnostic” stage in which the visual impressions are combained in such a way as
to assess a internal representation.
2. DISCONNECTION MODEL
In 1965 Geschwind’s view agnosia resulted from a disconnection between visual and verbal
processes. He cited anatomic evidence from the syndrome visual object agnosia, which in his
view was most often seen in the context of left mesial occipital lobe damage. According to
