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.

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.

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.

Visual agnosia is an impairment in recognition of visually presented objects. It is not due to a deficit in vision (acuity, visual field, and scanning), language, memory, or low intellect. While cortical blindness results from lesions to primary visual cortex, visual agnosia is often due to damage to more anterior cortex such as the posterior occipital and/or temporal lobe(s) in the brain. There are two types of visual agnosia: apperceptive agnosia and associative agnosia.

Recognition of visual objects occurs at two primary levels. At an apperceptive level, the features of the visual information from the retina are put together to form a perceptual representation of an object. At an associative level, the meaning of an object is attached to the perceptual representation and the object is identified. If a person is unable to recognize objects because they cannot perceive correct forms of the objects, although their knowledge of the objects is intact (i.e. they do not have anomia), they have apperceptive agnosia. If a person correctly perceives the forms and has knowledge of the objects, but cannot identify the objects, they have associative agnosia.

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.

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).

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.

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

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.

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.

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.

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.

Conduction aphasics will show relatively well-preserved auditory comprehension, which may even be completely functional. Spontaneous speech production will be fluent and generally grammatically and syntactically correct. Intonation and articulation will also be preserved. Speech will often contain paraphasic errors: phonemes and syllables will be dropped or transposed (e.g., "snowball" → "snowall", "television" → "vellitision", "ninety-five percent" → "ninety-twenty percent"). The hallmark deficit of this disorder, however, is in repetition. Patients will show a marked inability to repeat words or sentences when prompted by an examiner. After saying a sentence to a person with conduction aphasia, he or she will be able to paraphrase the sentence accurately but will not be able to repeat it, possibly because their "motor speech error processing is disrupted by inaccurate forward predictions, or because detected errors are not translated into corrective commands due to damage to the auditory-motor interface". When prompted to repeat words, patients will be unable to do so, and produce many paraphasic errors. For example, when prompted with "bagger", a patient may respond with, "gabber". Oral reading can also be poor.

However, patients recognize their paraphasias and errors and will try to correct them, with multiple attempts often necessary for success. This recognition is due to preserved auditory error detection mechanisms. Error sequences frequently fit a pattern of incorrect approximations featuring known morphemes that "a") share one or more similarly located phonemes but "b") differ in at least one aspect that makes the substituted morpheme(s) semantically distinct. This repetitive effort to approximate the appropriate word or phrase is known as "conduite d’approche". For example, when prompted to repeat "Rosenkranz", a German-speaking patient may respond with, "rosenbrau... rosenbrauch... rosengrau... bro... grosenbrau... grossenlau, rosenkranz... kranz... rosenkranz".

Conduction aphasia is a relatively mild language impairment, and most patients return to day-to-day life. Symptoms of conduction aphasia, as with other aphasias, can be transient, lasting only several hours or a few days. As aphasias and other language disorders are frequently due to stroke, their symptoms can change and evolve over time, or simply disappear. This is due to healing in the brain after inflammation or hemorrhage, which leads to decreased local impairment. Furthermore, plastic changes in the brain may lead to the recruitment of new pathways to restore lost function. For example, the right hemisphere speech systems may learn to correct for left-hemisphere damage. However, chronic conduction aphasia is possible, without transformation to other aphasias. These patients show prolonged, profound deficits in repetition, frequent phonemic paraphasias, and "conduite d'approche" during spontaneous speech.

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.

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".

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.

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.

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

Conduction aphasia, also called associative aphasia, is a relatively rare form of aphasia. An acquired language disorder, it is characterized by intact auditory comprehension, fluent (yet paraphasic) speech production, but poor speech repetition. They are fully capable of understanding what they are hearing, but fail to encode phonological information for production. This deficit is load-sensitive as patients show significant difficulty repeating phrases, particularly as the phrases increase in length and complexity and as they stumble over words they are attempting to pronounce. Patients will display frequent errors during spontaneous speech, such as substituting or transposing sounds. They will also be aware of their errors, and will show significant difficulty correcting them. For example: "Clinician: Now, I want you to say some words after me. Say ‘boy’. Patient: Boy. Clinician: Home. Patient: Home. Clinician: Seventy-nine. Patient: Ninety-seven. No … sevinty-sine … siventy-nice…. Clinician: Let’s try another one. Say ‘refrigerator’. Patient: Frigilator … no? how about … frerigilator … no frigaliterlater … aahh! It’s all mixed up!"

Shallice and Warrington (1970) were able to differentiate two variants of

this constellation: the reproduction and the repetition type. These authors suggested an exclusive deficit of auditory-verbal short-term memory in repetition conduction aphasia whereas the other variant was assumed to reflect disrupted phonological encoding mechanism, afflicting confrontation tasks such as repetition, reading and naming in a similar manner.

Left-hemisphere damage involving auditory regions often result in speech deficits. Lesions in this area that damage the sensorimotor dorsal stream suggest that the sensory system aid in motor speech. Studies have suggested that conduction aphasia is a result of damage specifically to the left superior temporal gyrus and/or the left supra marginal gyrus. The classical explanation for conduction aphasia is that of a disconnection between the brain areas responsible for speech comprehension (Wernicke's area) and speech production (Broca's area), due specifically to damage to the arcuate fasciculus, a deep white matter tract. Patients are still able to comprehend speech because the lesion does not disrupt the ventral stream pathway.

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.

Constructional apraxia is characterized by an inability or difficulty to build, assemble, or draw objects. Apraxia is a neurological disorder in which people are unable to perform tasks or movements even though they understand the task, are willing to complete it, and have the physical ability to perform the movements. Constructional apraxia may be caused by lesions in the parietal lobe following stroke or it may serve as an indicator for Alzheimer's disease.

Peripheral agraphias occurs when there is damage to the various motor and visualization skills involved in writing.

- Apraxic agraphia is the impairment in written language production associated with disruption of the motor system. It results in distorted, slow, effortful, incomplete, and/or imprecise letter formation. Though written letters are often so poorly formed that they are almost illegible, the ability to spell aloud is often retained. This form of agraphia is caused specifically by a loss of specialized motor plans for the formation of letters and not by any dysfunction affecting the writing hand. Apraxic agraphia may present with or without ideomotor apraxia. Paralysis, chorea, Parkinson's disease (micrographia), and dystonia (writer's cramp) are motor disorders commonly associated with agraphia.

- Hysterical agraphia is the impairment in written language production caused by a conversion disorder.

- Reiterative agraphia is found in individuals who repeat letters, words, or phrases in written language production an abnormal number of times. Preservation, paragraphia, and echographia are examples of reiterative agraphia.

- Visuospatial agraphia is the impairment in written language production defined by a tendency to neglect one portion (often an entire side) of the writing page, slanting lines upward or downward, and abnormal spacing between letters, syllables, and words. The orientation and correct sequencing of the writing will also be impaired. Visuospatial agraphia is frequently associated with left hemispatial neglect, difficulty in building or assembling objects, and other spatial difficulties.

Central agraphia occurs when there are both impairments in spoken language and impairments to the various motor and visualization skills involved in writing. Individuals who have agraphia with fluent aphasia write a normal quantity of well-formed letters, but lack the ability to write meaningful words. Receptive aphasia is an example of fluent aphasia. Those who have agraphia with nonfluent aphasia can write brief sentences but their writing is difficult to read. Their writing requires great physical effort but lacks proper syntax and often has poor spelling. Expressive aphasia is an example of nonfluent aphasia. Individuals who have Alexia with agraphia have difficulty with both the production and comprehension of written language. This form of agraphia does not impair spoken language.

- Deep agraphia affects an individuals' phonological ability and orthographic memory. Deep agraphia is often the result of a lesion involving the left parietal region (supramarginal gyrus or insula). Individuals can neither remember how words look when spelled correctly, nor sound them out to determine spelling. Individuals typically rely on their damaged orthographic memory to spell; this results in frequent errors, usually semantic in nature. Individuals have more difficulty with abstract concepts and uncommon words. Reading and spoken language are often impaired as well.

- Gerstmann syndrome agraphia is the impairment of written language production associated with the following structural symptoms: difficulty discriminating between one's own fingers, difficulty distinguishing left from right, and difficulty performing calculations. All four of these symptoms result from pathway lesions. Gerstmann's syndrome may additionally be present with alexia and mild aphasia.

- Global agraphia also impairs an individuals' orthographic memory although to a greater extent than deep agraphia. In global apraxia, spelling knowledge is lost to such a degree that the individual can only write very few meaningful words, or cannot write any words at all. Reading and spoken language are also markedly impaired.

- Lexical and structural agraphia are caused by damage to the orthographic memory; these individuals cannot visualize the spelling of a word, though they do retain the ability to sound them out. This impaired spelling memory can imply the loss or degradation of the knowledge or just an inability to efficiently access it. There is a regularity effect associated with lexical agraphia in that individuals are less likely to correctly spell words without regular, predictable spellings. Additionally, spelling ability tends to be less impaired for common words. Individuals also have difficulty with homophones. Language competence in terms of grammar and sentence writing tends to be preserved.

- Phonological agraphia is the opposite of lexical agraphia in that the ability to sound out words is impaired, but the orthographical memory of words may be intact. It is associated with a lexicality effect by a difference in the ability to spell words versus nonwords; individuals with this form of agraphia are depending on their orthographic memory. Additionally, it is often harder for these individuals to access more abstract words without strong semantic representations (i.e., it is more difficult for them to spell prepositions than concrete nouns).

- Pure agraphia is the impairment in written language production without any other language or cognitive disorder.

Agraphia can occur separately or co-occur and can be caused by damage to the angular gyrus