Agnosia is the inability to process sensory information. Often there 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. Agnosia only affects a single modality, such as vision or hearing.More recently, a top-down interruption is considered to cause the disturbance of handling perceptual information.

Also known as cerebral akinetopsia, this is associated with the inability to perceive visual motion. One cause of cerebral akinetopsia is lesions outside the striate cortex.

Patients cannot point at external targets located outside their own body, whether other persons' body parts or objects, but they perfectly point at their own body parts.

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.

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.

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.

Also known as somatosensory agnosia, it 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.

Auditory agnosia has been recognized since 1877. 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. There are two types of auditory agnosia: semantic associative and discriminative agnosia. Semantic associative agnosia is associated with lesions to the left hemisphere, whereas discriminative agnosia is associated with lesions to the right hemisphere.

Also known as pure word deafness (PWD). This presents as a form of meaning 'deafness' in which hearing is intact but there is significant difficulty recognising spoken words as semantically meaningful. Autotopagnosia 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.

A difficulty in perceiving colors in which the world may appear drab or in shades of gray. Cerebral achromatopsia is caused by neurological damage.There are two regions of the brain which specialize for color recognition, areas V4 and V8. If there is a unilateral lesion to area V4, a loss of color perception in only half of the visual field may result known as hemiachromatopsia. Similar, but distinct, is color agnosia, which involves having difficulty recognizing colors, while still being able to perceive them as measured by a color matching or categorizing task.

Refers to people who do not perceive any auditory information but whose hearing is intact. Environmental agnosia It is the inability to locate a specific room or building that one is familiar with, as well as the inability to provide directions for how to arrive at a particular location. These individuals experience difficulty with learning routes. This form of agnosia is often associated with lesions to the bilateral or right hemisphere posterior regions. It is also associated with prosopagnosia and Parkinson's disease.[3] 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.

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

Patients cannot point at another person's body parts, but can point at their own body parts.

Usually a patient has a form of associative agnosia or apperceptive agnosia. However, in the case of integrative agnosia a patient falls in between a form of associative and apperceptive 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.

Also referred to as congenital 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.

Inability to recognize text. Patients with pure alexia often have damage to their corpus callosum, as well as damage to the left visual association areas.[3] Pure alexia involves not being able to read printed material, but these individuals still have the ability to write. Individuals with pure alexia usually read words letter by letter. However, individuals with pure alexia show a frequency effect. They are able to read high frequency words better and faster than they can read low frequency words.

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).

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.

The inability to process visual input as a whole. The person instead processes faces, bodies, objects, rooms, places, pictures in a bit-by-bit fashion.[17] When looking at a picture they can describe the parts of the picture but struggle to comprehend the picture as a whole. Simultagnosia occurs in Bálint syndrome but may also occur in brain injury. This condition can also be described by only seeing one object at a time. An example is having two cups in your visual field and only being able to see one at a time.

Impaired ability to recognize or identify objects by touch alone.

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

Also known as topographical agnosia or topographagnosia, 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 recognize objects. Nevertheless, they may still have an excellent capacity to describe the visual layout of the same place. Patients with topographical agnosia have the ability to read maps, but become lost in familiar environments.

This is a loss of the sense of whereness in the relation of oneself to one's environment and in the relation of objects to each other. It may include constructional apraxia, topographical disorientation, optic ataxia, ocular motor apraxia, dressing apraxia, and right-left confusion.

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