Describe some of the specific vision impairments (visual agnosia, prosopagnosia, apperceptive agnosia, apraxia, akinotopsia). What do these impairments tell us about brain bases of perception?

Describe some of the specific vision impairments (visual agnosia, prosopagnosia, apperceptive agnosia, apraxia, akinotopsia). What do these impairments tell us about brain bases of perception?

Visual Agnosia is the inability to recognize visual stimuli. Visual Agnosia is not caused by damage to the sensory organs such as the eye, retina, or optic tract. Individuals who suffer from Visual Agnosia are able to see well but cannot perceive, or make sense of the information that they see. Visual Agnosia seems to occur when there is damage to visual processing areas of the brain such as the parietal lobe or occipital lobe. Agnosia means "loss of knowledge" in Greek, this is very fitting because it seems that patients who suffer from Agnosias lose their knowledge in a specific category.

Prosopagnosia, also called face blindness, is an impairment in the recognition of faces. It is often accompanied by other types of recognition impairments (place recognition, car recognition, facial expression of emotion, etc.) though sometimes it appears to be restricted to facial identity. Not surprisingly, prosopagnosia can create serious social problems. Prosopagnosics often have difficulty recognizing family members, close friends, and even themselves. They often use alternative routes to recognition, but these routes are not as effective as recognition via the face.

Apperceptive agnosia –Apperceptive visual agnosia is characterised by an intact visual ability on a basic sensory level, but a defect in early stage visual processing prevents a correct percept of the stimulus being formed. The patient is unable to access the structure or spatial properties of a visual stimuli and the object is not seen as a whole or in a meaningful way. Stroke, anoxia and carbon monoxide poisoning are common causes and it is often associated with diffuse, posterior lesions. Patients fail tests such as visual matching, discriminating shapes, comparing similar figures and copying drawings.

Apraxia is characterized by loss of the ability to execute or carry out learned purposeful movements despite having the desire and the physical ability to perform the movements. It is a disorder of motor planning, which may be acquired or developmental, but is not caused by incoordination, sensory loss, or failure to comprehend simple commands (which can be tested by asking the person to recognize the correct movement from a series). It is caused by damage to specific areas of the cerebrum.

Akinotopsia also known as motion blindness, is an extremely rare neuropsychological disorder in which a patient cannot perceive motion in their visual field, despite being able to see stationary objects without issue. For patients with akinetopsia, the world becomes devoid of motion. Most of what is known about akinetopsia was learned through the case study of one patient, LM.

These impairments tell us that the brain makes an error in processing the information which the eye takes in.

Visual agnosia-> is the inability to recognize familiar objects, eventhough there is no sensory deficit

Prosopagnosia-> is the inability to recognize faces. This is based on the damage of the fusiform area as this specific brain area is important in perception of faces.

Apperceptive agnosia-> is the impairment in judging even basic aspects of form or shape of objects. E.g. inability to describe a line as vertical, horizontal or tilted.

Apraxia -> is a neurological disorder that impairs the ability to make voluntary movement, especially in manipulation of objects. When the left hemisphere of our brain is damaged, imitation is impaired as it is dominant for the control of action. Hence if imitation-perception based is impaired, this is a problem.

Akinotopsia-> or motion blindness, is the loss of ability to see objects move. Patients with motion blindess have difficulties making judgements about moving things.