Monday, 8 March 2010

Types of Agnosias

Agnosia literally meaning “loss of knowledge” is a loss of ability to recognize objects, persons, sounds, shapes, or smells while the specific sense is not defective nor is there any significant memory loss. It is usually associated with brain injury or neurological illness, particularly after damage to the occipitotemporal border, which is part of the ventral stream

Inability to recognize text.

Whilst not strictly a form of agnosia, alexithymia may be difficult to distinguish from or co-occur with social-emotional agnosia. Alexithymia is deficiency in understanding, processing, or describing emotions common to around 85% of people on the autism spectrum. Alexithymia is believed to be due to an information processing delay in the combined processing of information in the left and right hemispheres, resulting in poor differentiation between body messages and emotions.

Or receptive amusia is agnosia for music. It involves loss of the ability to recognize musical notes, rhythms, and intervals and the inability to experience music as musical.

This is the inability to gain feedback about one's own condition and can be confused with lack of insight but is caused by problems in the feedback mechanisms in the brain. It is caused by neurological damage and can occur in connection with a range of neurological impairments but is most commonly referred to in cases of paralysis following stroke. Those with Anosognosia with multiple impairments may even be aware of some of their impairments but completely unable to perceive others.

Apperceptive agnosia
Patients are unable to distinguish visual shapes and so have trouble recognizing, copying, or discriminating between different visual stimuli. Unlike patients suffering from associative agnosia, those with apperceptive agnosia are unable to copy images.

Is a form of motor (body) agnosia involving the neurological loss of ability to map out physical actions in order to repeat them in functional activities. It is a form of body-disconnectedness and takes several different forms; Speech-Apraxia in which ability to speak is impaired, Limb-Kinetic Apraxia in which there is a loss of hand or finger dexterity and can extend to the voluntary use of limbs, Ideomotor Apraxia in which the gestures of others can't be easily replicated and can't execute goal-directed movements, Ideational Apraxia in which one can't work out which actions to initiate and struggles to plan and discriminate between potential gestures, Apraxia of Gait in which co-ordination of leg actions is problematic such as kicking a ball, Constructional Apraxia in which a person can't co-ordinate the construction of objects or draw pictures or follow a design, Oculomotor Apraxia in which the ability to control visual tracking is impaired and Buccofacial Apraxia in which skilled use of the lips, mouth and tongue is impaired.

Associative agnosia
Patients can describe visual scenes and classes of objects but still fail to recognize them. They may, for example, know that a fork is something you eat with but may mistake it for a spoon. Patients suffering from associative agnosia are still able to reproduce an image through copying.

Auditory agnosia
With Auditory Agnosia there is difficulty distinguishing environmental and non-verbal auditory cues including difficulty distinguishing speech from non-speech sounds even though hearing is usually normal.

Is associated with the inability to orient parts of the body, and is often caused by a lesion in the parietal part of the posterior thalmic radiations.

Color agnosia
Refers to the inability to recognize a color, while being able to perceive or distinguish it.

Cortical deafness
Refers to people who do not perceive any auditory information but whose hearing is intact.

Finger agnosia
Is the inability to distinguish the fingers on the hand. It is present in lesions of the dominant parietal lobe, and is a component of Gerstmann syndrome.

Form agnosia
Patients perceive only parts of details, not the whole object.

Integrative agnosia
This is where one has the ability to recognize elements of something but yet be unable to integrate these elements together into comprehensible perceptual wholes.

Mirror agnosia
One of the symptoms of Hemispatial neglect. Patients with Hemispatial neglect were placed so that an object was in their neglected visual field but a mirror reflecting that object was visible in their non-neglected field. Patients could not acknowledge the existence of objects in the neglected field and so attempted to reach into the mirror to grasp the object.

Pain agnosia
Also referred to as Analgesia, this is the difficulty perceiving and processing pain; thought to underpin some forms of self injury.

Is the inability to recognize familiar voices, even though the hearer can understand the words used.

Also known as faceblindness and facial agnosia: Patients cannot consciously recognize familiar faces, sometimes even including their own. This is often misperceived as an inability to remember names.

Semantic agnosia
Those with this form of agnosia are effectively 'object blind' until they use non-visual sensory systems to recognise the object. For example, feeling, tapping, smelling, rocking or flicking the object, may trigger realisation of its semantics (meaning).

Patients can recognize objects or details in their visual field, but only one at a time. They cannot make out the scene they belong to or make out a whole image out of the details. They literally "cannot see the forest for the trees." Simultanagnosia is a common symptom of Balint's syndrome.

Social emotional agnosia
Sometimes referred to as Expressive Agnosia, this is a form of agnosia in which the person is unable to perceive facial expression, body language and intonation, rendering them unable to non-verbally perceive people's emotions and limiting that aspect of social interaction.

Somatosensory agnosia
Or Astereognosia] is connected to tactile sense - that is, touch. Patient finds it difficult to recognize objects by touch based on its texture, size and weight. However, they may be able to describe it verbally or recognize same kind of objects from pictures or draw pictures of them. Thought to be connected to lesions or damage in somatosensory cortex.

Tactile agnosia
Impaired ability to recognize or identify objects by touch alone.

Time agnosia
Is the loss of comprehension of the succession and duration of events.

Topographical agnosia
This is a form of visual agnosia in which a person cannot rely on visual cues to guide them directionally due to the inability to recognise objects. Nevertheless, they may still have an excellent capacity to describe the visual layout of the same place

Verbal auditory agnosia
This presents as a form of meaning 'deafness' in which hearing is intact but there is significant difficulty recognising spoken words as semantically meaningful.[19]

Visual agnosia
Is associated with lesions of the left occipital lobe and temporal lobes. Many types of visual agnosia involve the inability to recognize objects.

Visual verbal agnosia
Difficulty comprehending the meaning of written words. The capacity to read is usually intact but comprehension is impaired.]

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