Cognitive neuroscience of visual object recognition
Agnosia is a rare occurrence and can be the result of a stroke, dementia, head injury, brain infection, or hereditary.
Apperceptive agnosia is a deficit in object perception creating an inability to understand the significance of objects.
Similarly, associative visual agnosia is the inability to understand the significance of objects; however, this time the deficit is in semantic memory. Both of these agnosias can affect the pathway to object recognition, like Marr's Theory of Vision. More specifically unlike apperceptive agnosia, associative agnosic patients are more successful at drawing, copying, and matching tasks; however, these patients demonstrate that they can perceive but not recognize.
Integrative agnosia(a subtype of associative agnosia) is the inability to integrate separate parts to form a whole image. With these types of agnosias there is damage to the ventral (what) stream of the visual processing pathway.
Object orientation agnosia is the inability to extract the orientation of an object despite adequate object recognition. With this type of agnosia there is damage to the dorsal (where) stream of the visual processing pathway.
This can affect object recognition in terms of familiarity and even more so in unfamiliar objects and viewpoints.
A difficulty in recognizing faces can be explained by prosopagnosia. Someone with prosopagnosia cannot identify the face but is still able to perceive age, gender, and emotional expression. The brain region that specifies in facial recognition is the fusiform face area. Prosopagnosia can also be divided into apperceptive and associative subtypes. Recognition of individual chairs, cars, animals can also be impaired; therefore, these object share similar perceptual features with the face that are recognized in the fusiform face area.
Self-awareness
Anosognosia was a term coined by Joseph Babinski to describe the clinical condition in which an individual suffered from left hemiplegia following a right cerebral hemisphere stroke yet denied that there were any problems with their left arm or leg. This condition is known as anosognosia for hemiplegia (AHP). This condition has evolved throughout the years and is now used to describe people who lack subjective experience in both neurological and neuropsychological cases. A wide variety of disorders are associated with anosognosia. For example, patients who are blind from cortical lesions might in fact be unaware that they are blind and may state that they do not suffer from any visual disturbances. Individuals with aphasia and other cognitive disorders may also suffer from anosognosia as they are unaware of their deficiencies and when they make certain speech errors, they may not correct themselves due to their unawareness. Individuals who suffer from Alzheimer's disease lack awareness; this deficiency becomes more intense throughout their disease. A key issue with this disorder is that people who do have anosognosia and suffer from certain illnesses may not be aware of them, which ultimately leads them to put themselves in dangerous positions and/or environments. To this day there are still no available treatments for AHP, but it has been documented that temporary remission has been used following vestibular stimulation.