Agnosias are sensory modality specific, usually classified as visual, auditory, or tactile. Associative visual agnosia refers to a subtype of visual agnosia, which was labeled by Lissauer (1890), as an inability to connect the visual percept (mental representation of something being perceived through the senses) with its related semantic information stored in memory, such as, its name, use, and description. This is distinguished from the visual apperceptive form of visual agnosia, "apperceptive visual agnosia", which is an inability to produce a complete percept, and is associated with a failure in higher order perceptual processing where feature integration is impaired, though individual features can be distinguished. In reality, patients often fall between both distinctions, with some degree of perceptual disturbances exhibited in most cases, and in some cases, patients may be labeled as integrative agnostics when they fit the criteria for both forms. Associative visual agnosias are often category-specific, where recognition of particular categories of items are differentially impaired, which can affect selective classes of stimuli, larger generalized groups or multiple intersecting categories. For example, deficits in recognizing stimuli can be as specific as familiar human faces or as diffuse as living things or non-living things.

An agnosia that affects hearing, "auditory sound agnosia", is broken into subdivisions based on level of processing impaired, and a "semantic-associative" form is investigated within the auditory agnosias.

Visual agnosia is a broad category that refers to a deficiency in the ability to recognize visual objects. Visual agnosia can be further subdivided into two different subtypes: apperceptive visual agnosia and associative visual agnosia.

Individuals with apperceptive visual agnosia display the ability to see contours and outlines when shown an object, but they experience difficulty if asked to categorize objects. Apperceptive visual agnosia is associated with damage to one hemisphere, specifically damage to the posterior sections of the right hemisphere.

In contrast, individuals with associative visual agnosia experience difficulty when asked to name objects. Associative agnosia is associated with damage to both the right and left hemispheres at the occipitotemporal border. A specific form of associative visual agnosia is known as prosopagnosia. Prosopagnosia is the inability to recognize faces. For example, these individuals have difficulty recognizing friends, family and coworkers. However, individuals with prosopagnosia can recognize all other types of visual stimuli.

The two main categories of visual agnosia are:

- Apperceptive visual agnosia, impaired object recognition. Individuals with apperceptive visual agnosia cannot form a whole percept of visual information.

- Associative visual agnosia, impaired object identification. Individuals with associative agnosia cannot give a meaning to a formed percept. The percept is created, but it would have no meaning for individuals who have an associative agnosia.

Associative visual agnosia is a form of visual agnosia. It is an impairment in recognition or assigning meaning to a stimulus that is accurately perceived and not associated with a generalized deficit in intelligence, memory, language or attention. The disorder appears to be very uncommon in a "pure" or uncomplicated form and is usually accompanied by other complex neuropsychological problems due to the nature of the etiology. Afflicted individuals can accurately distinguish the object, as demonstrated by the ability to draw a picture of it or categorize accurately, yet they are unable to identify the object, its features or its functions.

Symptoms generally include memory or learning impairments, with the inability to integrate parts coherently.There is a big range to the severity of this disease and often the symptoms that are shown in each patient vary as well. As ambiguous as the general symptoms may be, patients are often treated of their respective symptoms as they appear and how critical the conditions are.

Apperceptive agnosia is a failure in recognition that is due to a failure of perception. In contrast, associative agnosia is a type of agnosia where perception occurs but recognition still does not occur. When referring to apperceptive agnosia, visual and object agnosia are most commonly discussed; This occurs because apperceptive agnosia is most likely to present visual impairments. However, in addition to visual apperceptive agnosia there are also cases of apperceptive agnosia in other sensory areas.

Broadly, visual agnosia is divided into apperceptive and associative visual agnosia.

Apperceptive agnosia is failure of object recognition even when the basic visual functions (acuity, color, motion) and other mental processing, such as language and intelligence, are normal. The brain must correctly integrate features such as edges, light intensity, and color from sensory information to form a complete percept of an object. If a failure occurs during this process, a percept of an object is not fully formed and thus it cannot be recognized. Tasks requiring copying, matching, or drawing simple figures can distinguish the individuals with apperceptive agnosia because they cannot perform such tasks.

Associative agnosia is an inability to identify objects even with apparent perception and knowledge of them. It involves a higher level of processing than apperceptive agnosia. Individuals with associative agnosia can copy or match simple figures, indicating that they can perceive objects correctly. They also display the knowledge of objects when tested with tactile or verbal information. However, when tested visually, they cannot name or describe common objects. This means that there is an impairment in associating the perception of objects with the stored knowledge of them.

Although visual agnosia can be general, there exist many variants that impair recognition of specific types. These variants of visual agnosia include prosopagnosia (inability to recognize faces), pure word blindness (inability to recognize words, often called "agnosic alexia" or "pure alexia"), agnosias for colors (inability to differentiate colors), agnosias for the environment (inability to recognize landmarks or difficult with spatial layout of an environment, i.e. topographagnosia) and simultanagosia (inability to sort out multiple objects in a visual scene).

Auditory verbal agnosia can be referred to as a pure aphasia because it has a high degree of specificity. Despite an inability to comprehend speech, patients with auditory verbal agnosia typically retain the ability to hear and process non-speech auditory information, speak, read and write. This specificity suggests that there is a separation between speech perception, non-speech auditory processing, and central language processing. In support of this theory, there are cases in which speech and non-speech processing impairments have responded differentially to treatment. For example, some therapies have improved writing comprehension in patients over time, while speech remained critically impaired in those same patients.

The term "pure word deafness" is something of a misnomer. By definition, individuals with pure word deafness are not deaf – in the absence of other impairments, these individuals have normal hearing for all sounds, including speech. The term "deafness" originates from the fact that individuals with AVA are unable to "comprehend" speech that they hear. The term "pure word" refers to the fact that comprehension of verbal information is selectively impaired in AVA. For this reason, AVA is distinct from other auditory agnosias in which the recognition of nonspeech sounds is impaired. Classical (or pure) auditory agnosia is an inability to process environmental sounds. Interpretive or receptive agnosia (amusia) is an inability to understand music.

Patients with pure word deafness complain that speech sounds simply do not register, or that they tend not to come up. Other claims include speech sounding as if it were in a foreign language, the words having a tendency to run together, or the feeling that speech was simply not connected to the patient's voice.

Integrative agnosia is a sub-disease of agnosia, meaning the lack of integrating perceptual wholes within

knowledge. Integrative agnosia can be assessed by several experimental tests such as the Efron shape test, which

determines the specificity of the disease being Integrative.

This disease is often caused by brain trauma, producing medial ventral lesions to the extrastriate cortex. Affecting this region of the brain produces learning impairments: the inability to

integrate parts such as spatial distances or producing visual images from short or long-term memory.

Speech agnosia, or auditory verbal agnosia, refers to "an inability to comprehend spoken words despite intact hearing, speech production and reading ability". Patients report that they do indeed hear sounds being produced, but that the sounds are fundamentally unrecognizable/untranslatable.

1. EXAMINER: What did you eat for breakfast?

2. PATIENT: Breakfast, breakfast, it sounds familiar but it doesn't speak to me. (Obler & Gjerlow 1999:45)

Despite an inability to process what the speaker is saying, some patients have been reported to recognize certain characteristic information about the speaker's voice (such as being a man or woman).

Auditory agnosia is a form of agnosia that manifests itself primarily in the inability to recognize or differentiate between sounds. It is not a defect of the ear or "hearing", but a neurological inability of the brain to process sound meaning. It is a disruption of the "what" pathway in the brain. Persons with auditory agnosia can physically hear the sounds and describe them using unrelated terms, but are unable to recognize them. They might describe the sound of some environmental sounds, such as a motor starting, as resembling a lion roaring, but would not be able to associate the sound with "car" or "engine", nor would they say that it "was" a lion creating the noise. Auditory agnosia is caused by damage to the secondary and tertiary auditory cortex of the temporal lobe of the brain.

There are three primary distinctions of auditory agnosia that fall into two categories.

Auditory verbal agnosia (AVA), also known as pure word deafness, is the inability to comprehend speech. Individuals with this disorder lose the ability to understand language, repeat words, and write from dictation. Some patients with AVA describe hearing spoken language as meaningless noise, often as though the person speaking was doing so in a foreign language. However, spontaneous speaking, reading, and writing are preserved. The maintenance of the ability to process non-speech auditory information, including music, also remains relatively more intact than spoken language comprehension. Individuals who exhibit pure word deafness are also still able to recognize non-verbal sounds. The ability to interpret language via lip reading, hand gestures, and context clues is preserved as well. Sometimes, this agnosia is preceded by cortical deafness; however, this is not always the case. Researchers have documented that in most patients exhibiting auditory verbal agnosia, the discrimination of consonants is more difficult than that of vowels, but as with most neurological disorders, there is variation among patients.

Auditory verbal agnosia (AVA) is not the same as Auditory agnosia; patients with (nonverbal) auditory agnosia have a relatively more intact speech comprehension system despite their impaired recognition of nonspeech sounds.

The syndrome rarely presents itself the same way in every patient. Some symptoms that occur may be:

- Constructional apraxia: difficulty in constructing: drawing, copying, designs, copying 3D models

- Topographical disorientation: difficulty finding one's way in the environment

- Optic ataxia: deficit in visually-guided reaching

- Ocular motor apraxia: inability to direct gaze, a breakdown (failure) in starting (initiating) fast eye movements

- Dressing apraxia: difficulty in dressing usually related to inability to orient clothing spatially, and to a disrupted awareness of body parts and the position of the body and its parts in relation to themselves and objects in the environment

- Right-left confusion: difficulty in distinguishing the difference between the directions left and right

Patients with autotopagnosia exhibit an inability to locate parts of their own body, the body of an examiner’s, or the parts of a representation of a human body. Deficiencies can be in localizing parts of a certain area of the body, or the entire body.

Some patients demonstrating the symptoms of autotopagnosia have a decreased ability to locate parts of other multipart object. Patients are considered to suffer from “pure” autotopagnosia, however, if their deficiency is specific to body part localization. Patients suffering from “pure” autotopagnosia often have no problems carrying out tasks involved in everyday life that require body part awareness. Patients have difficulty locating body parts when directly asked, but can carry out activities such as putting on pants without difficulty. Patients can describe the function and appearance of body parts, yet they are still unable to locate them.

Damage to the left parietal lobe can result in what is called Gerstmann syndrome. It can include right-left confusion, a difficulty with writing Agraphia and a difficulty with mathematics Acalculia. In addition, it can also produce language deficiencies Aphasia and an inability to recognize objects normally Agnosia.

Other related disorders include:

- Apraxia: an inability to perform skilled movements despite understanding of the movements and intact sensory and motor systems.

- Finger agnosia: An inability to name the fingers, move a specific finger upon being asked, and/or recognize which finger has been touched when an examiner touches one.

Topographical disorientation, also known as topographical agnosia and topographagnosia, is the inability to orient oneself in one's surroundings as a result of focal brain damage. This disability may result from the inability to make use of selective spatial information (e.g., environmental landmarks) or to orient by means of specific cognitive strategies such as the ability to form a mental representation of the environment, also known as a cognitive map. It may be part of a syndrome known as visuospatial dysgnosia.

Prosopagnosia, also called face blindness, is a cognitive disorder of face perception in which the ability to recognize familiar faces, including one's own face (self-recognition), is impaired, while other aspects of visual processing (e.g., object discrimination) and intellectual functioning (e.g., decision making) remain intact. The term originally referred to a condition following acute brain damage (acquired prosopagnosia), but a congenital or developmental form of the disorder also exists, which may affect up to 2.5% of the United States population. The specific brain area usually associated with prosopagnosia is the fusiform gyrus, which activates specifically in response to faces. The functionality of the fusiform gyrus allows most people to recognize faces in more detail than they do similarly complex inanimate objects. For those with prosopagnosia, the new method for recognizing faces depends on the less-sensitive object recognition system. The right hemisphere fusiform gyrus is more often involved in familiar face recognition than the left. It remains unclear whether the fusiform gyrus is only specific for the recognition of human faces or if it is also involved in highly trained visual stimuli.

There are two types of prosopagnosia: acquired and congenital (developmental). Acquired prosopagnosia results from occipito-temporal lobe damage and is most often found in adults. This is further subdivided into apperceptive and associative prosopagnosia. In congenital prosopagnosia, the individual never adequately develops the ability to recognize faces.

Though there have been several attempts at remediation, no therapies have demonstrated lasting real-world improvements across a group of prosopagnosics. Prosopagnosics often learn to use "piecemeal" or "feature-by-feature" recognition strategies. This may involve secondary clues such as clothing, gait, hair color, skin color, body shape, and voice. Because the face seems to function as an important identifying feature in memory, it can also be difficult for people with this condition to keep track of information about people, and socialize normally with others. Prosopagnosia has also been associated with other disorders that are associated with nearby brain areas: left hemianopsia (loss of vision from left side of space, associated with damage to the right occipital lobe), achromatopsia (a deficit in color perception often associated with unilateral or bilateral lesions in the temporo-occipital junction) and topographical disorientation (a loss of environmental familiarity and difficulties in using landmarks, associated with lesions in the posterior part of the parahippocampal gyrus and anterior part of the lingual gyrus of the right hemisphere). It is from the Greek: "prosopon" = "face" and "agnosia" = "not knowing".

Visuospatial dysgnosia 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. Visuospatial dysgnosia is often linked with topographical disorientation.

Autotopagnosia from the Greek "a" and "gnosis," meaning "without knowledge", "topos" meaning "place", and "auto" meaning "oneself", autotopagnosia virtually translates to the "lack of knowledge about one's own space," and is clinically described as such.

Autotopagnosia is a form of agnosia, characterized by an inability to localize and orient different parts of the body. The psychoneurological disorder has also been referred to as "body-image agnosia" or "somatotopagnosia." "Somatotopagnosia" has been argued to be a better suited term to describe the condition. While autotopagnosia emphasizes the deficiencies in localizing only one's own body parts and orientation, "somatotopagnosia" also considers the inability to orient and recognize the body parts of others or representations of the body (e.g., manikins, diagrams).

Typically, the cause of autotopagnosia is a lesion found in the parietal lobe of the left hemisphere of the brain. However, it as also been noted that patients with generalized brain damage present with similar symptoms of autotopagnosia.

As a concept, autotopagnosia has been criticized as nonspecific; some claim that this is a manifestation of a greater symptomatic complex of anomia, marked by an inability to name things in general—not just parts of the human body.

Topographical disorientation is the inability to orient in the surrounding as a result of focal brain damage.

Topographical Disorientation has been studied for decades using case studies of patients who have selectively lost their ability to find their way within large-scale, locomotor environments. Several dozen case reports of topographical disorientation have been presented over the last century. Studying these people will aid in the understanding of the complex, multi-component behavior of navigation. Topographical disorientation may result from a stroke or part of a progressive illness, hemispatial neglect, dementia, Alzheimer's disease.

"Associative prosopagnosia" has typically been used to describe cases of acquired prosopagnosia with spared perceptual processes but impaired links between early face perception processes and the semantic information we hold about people in our memories. Right anterior temporal regions may also play a critical role in associative prosopagnosia. People with this form of the disorder may be able to see whether photos of people's faces are the same or different and derive the age and sex from a face (suggesting they can make sense of some face information) but may not be able to subsequently identify the person or provide any information about them such as their name, occupation, or when they were last encountered.

Patients with finger agnosia may have difficulty selectively moving fingers, regardless if it is by command or imitation. Others show an inability to name or point to others' fingers, or to show the same finger on the opposite hand. Persons with finger agnosia are able to name and point to a finger when able to use visual guidance, but will have more errors than a person without the disorder. When their own hand is out of sight and they are asked to name a finger that was touched, they are unable to do so and perform at chance.

Social-emotional agnosia is generally diagnosed through the use of two tests, the Faux Pas Test and the Strange Stories Test. Both of these tests are used to show deficits in theory of mind, the recognition of mental states of others. For people with social-emotional agnosia, it is mainly the emotional states that are difficult for them to recognize. Studies have shown that subjects with amygdala damage perform poorly on both the Faux Pas test and the Strange Stories test.

Social-emotional agnosia, also known as emotional agnosia or expressive agnosia, is the inability to perceive facial expressions, body language, and voice intonation. A person with this disorder is unable to non-verbally perceive others' emotions in social situations, limiting normal social interactions. The condition causes a functional blindness to subtle non-verbal social-emotional cues in voice, gesture, and facial expression. People with this form of agnosia have difficulty in determining and identifying the motivational and emotional significance of external social events, and may appear emotionless or agnostic (uncertainty or general indecisiveness about a particular thing). Symptoms of this agnosia can vary depending on the area of the brain affected. Social-emotional agnosia often occurs in individuals with schizophrenia and autism. It is difficult to distinguish from, and has been found to co-occur with, alexithymia.

Phonagnosia (from Ancient Greek φωνή "phone", "voice" and γνῶσις "gnosis", "knowledge") is a type of agnosia, or loss of knowledge, that involves a disturbance in the recognition of familiar voices and the impairment of voice discrimination abilities in which the affected individual does not suffer from comprehension deficits. Phonagnosia is an auditory agnosia, an acquired auditory processing disorder resulting from brain damage, other auditory agnosias include cortical deafness and auditory verbal agnosia also known as pure word deafness.

Since people suffering from phonagnosia do not suffer from aphasia, it is suggested that the structures of linguistic comprehension are functionally separate from those of the perception of the identity of the speaker who produced it.

Phonagnosia is the auditory equivalent of prosopagnosia. Unlike Prosopagnosia, investigations of phonagnosia have not been extensively pursued. Phonagnosia was first described by a study by Van Lancker and Cantor in 1982. The subjects in this study were asked to identify which of four names or faces matched a specific famous voice. The subjects could not complete the task. Since then, there have been a couple studies done on patients with phonagnosia. The clinical and radiologic findings with computerized tomographic scans cat scan in these cases suggest that recognition of familiar voices is impaired by damage to the inferior and parietal regions of the right hemisphere while voice discrimination is impaired by temporal lobe damage of either hemisphere. These studies have also shown evidence for a double dissociation between voice recognition and voice discrimination. Some patients will perform normally on the discrimination tasks but poorly on the recognition tasks; whereas the other patients will perform normally on the recognition tasks but poorly on the discrimination tasks. Patients did not perform poorly on both tasks.

Associative phonagnosia is a form of phonagnosia that develops with dementia or other focal neurodegenerative disorders. Some research has led to questions of other impairments in phonagnosics. Recently, studies have shown that phonagnosics also have trouble in recognizing the sounds of familiar instruments. As it is with voices, they also show deficiency in distinguishing between sounds from different instruments. Although the disability is shown, phonagnosics are much less affected in this area of sound discrimination. In distinguishing voices, it is a complete agnosia, but this is not the case for musical instrument sounds, as they can correctly identify some of them. Controversy arises in that not all phonagnosics exhibit these symptoms, and so not all researchers agree that it should be attributed to the damage suffered that causes phonagnosia. Much debate has arisen over the fact that it seems that separate areas of the brain are utilized to handle information from language and music. This has led some researchers to skeptically consider this impairment as a clear symptom of the disorder. Again, more research is needed to create a clearer conclusion.

An interesting attribute that phonagnosics possess is that they can correctly detect emotions in voices when someone talks to them. They can also correctly match an emotion with a facial expression. Although surprising, this finding is sensible because it is known and well agreed upon that the limbic system, involved in expressing emotions and detecting emotions of others, is a separate system within the brain. The limbic system is made up of several brain structures including the hippocampus, amygdala, anterior thalamic nuclei, septum, limbic cortex and fornix.

Presently, there is no therapy or treatment for phonagnosia. Clearly, more research is needed to accomplish the feat of developing treatment for the disorder. The lack of treatment stems from the lack of knowledge about the disorder. Increased research will reveal vital information needed to formulate effective treatments and therapies.