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Amorphagnosia
Amorphagnosia is the inability to recognize the size and
shape of objects. Amorphagnosia is a form of agnosia.
Agnosia is a loss of the ability to recognize a specific
type of sensory input even though the specific sense is
not defective. For example, even though the sense of
touch and vision is intact in amorphagnosia, the person
cannot use these senses to make size and shape
discriminations. Agnosia is usually caused by brain
injury/damage, particularly in the posterior (back) part of
the brain.
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The posterior parietal lobe is known to play a specialized role in shape recognition. The
parietal lobe is the middle area of the top part of the brain and is responsible for
integrating sensory information to form perceptions. The parietal lobe is located on both
sides of the brain.
Amorphagnosia usually affects the hand on the opposite side of the damaged brain
region. For example, left parietal brain damage would cause amorphagnosia for objects
placed in the right hand. However, both hands can be affected to the same degree in
cases where both sides of the brain have been damaged. An example would be a stroke
on both sides of the brain. A stroke is a burst artery (a type of blood vessel that carries
blood away from the heart) or a blockage of an artery in the brain.
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When amorphagnosia affects both hands, it could be caused by
damage to both parietal lobes. However, Saetti et al. (1999)
proposed a mechanism by which an inability to recognize shapes in
both hands (which they referred to as morphagnosia) resulted from
a severe spatial deficit, especially for line orientation detection.
Amorphagnosia comes from the Greek word “a” meaning “without,”
the Greek word “morphe” meaning “shape,” and the Greek word
“gnosis” meaning “knowledge.” Put the word together and you get
“without shape knowledge.”
Reference: Saetti, MC, De Renzi E, Comper M. (1999). Tactile morphagnosia
secondary to spatial deficits. Neuropsychologia. 37(9), 1087-100.
