Phonological dyslexia is a reading disability that is a form of alexia (acquired dyslexia), resulting from brain injury, stroke, or progressive illness and that affects previously acquired reading abilities. The major distinguishing symptom of acquired phonological dyslexia is that a selective impairment of the ability to read pronounceable non-words occurs although the ability to read familiar words is not affected. It has also been found that the ability to read non-words can be improved if the non-words belong to a family of pseudohomophones.

Deep dyslexia is usually classified as an "acquired reading disorder", as opposed to a "developmental dyslexia", in previously literate adults as a consequence of a brain injury. However, recently, developmental deep dyslexia has also been reported in children with Williams syndrome.

Deep dyslexia is considered to be a "central dyslexia" as compared to a "peripheral dyslexia". Peripheral dyslexics have difficulty matching the visual characteristics of letters that comprise a word to a stored memory of this word from prior encounters. Central dyslexics are unable to properly match the visual word to the word's meaning. They may also be incapable of speaking, or phonating, the sequence of written letters that they see into the word these letters represent. Deep dyslexia differs from other forms of central dyslexia (phonological dyslexia and surface dyslexia) in that deep dyslexics have many more symptoms and these symptoms are generally more severe. According to the "continuum" hypothesis, deep dyslexia is a more severe form of phonological dyslexia.

Deep dyslexia is a form of dyslexia that disrupts reading processes. Deep dyslexia may occur as a result of a head injury, stroke, disease, or operation. This injury results in the occurrence of semantic errors during reading and the impairment of nonword reading.

The term dyslexia comes from the Greek words 'dys' meaning 'impaired', and 'lexis' meaning 'word' and is used to describe disorders of language concerning reading and spelling.

Numerous models and hypotheses have been proposed in attempt to explain the broad range of symptoms experienced by deep dyslexics, but a definite consensus has yet to be reached. The proposed models and hypotheses have helped in treatment of some suffering patients, but only with certain specific symptoms. Additionally, the recovery seen is not experienced equally in all patients.

Pure alexia results from cerebral lesions in circumscribed brain regions and therefore belongs to the group of acquired reading disorders, alexia, as opposed to developmental dyslexia found in children who have difficulties in learning to read.

Pure alexia, also known as agnosic alexia or alexia without agraphia or pure word blindness, is one form of alexia which makes up "the peripheral dyslexia" group. Individuals who have pure alexia suffer from severe reading problems while other language-related skills such as naming, oral repetition, auditory comprehension or writing are typically intact.

Pure alexia is also known as: "alexia without agraphia", "letter-by-letter dyslexia", "spelling dyslexia", or "word-form dyslexia". Another name for it is "Dejerine syndrome", after Joseph Jules Dejerine, who described it in 1892; however, when using this name, it should not be confused with medial medullary syndrome which shares the same eponym.

Surface dyslexia is a type of dyslexia, or reading disorder. According to Marshall & Newcombe's (1973) and McCarthy & Warrington's study (1990), patients with this kind of disorder cannot recognize a word as a whole due to the damage of the left parietal or temporal lobe. Individuals with surface dyslexia are unable to recognize a word as a whole word and retrieve its pronunciation from memory. Rather, individuals with surface dyslexia rely on pronunciation rules. Thus, patients with this particular type of reading disorder read non-words fluently, like "yatchet", but struggle with words that defy pronunciation rules (i.e. exception words). For example, a patient with surface dyslexia can correctly read regular words like "mint", but will err when presented a word that disobeys typical pronunciation rules, like "pint". Often, semantic knowledge is preserved in individuals with surface dyslexia.

Dysgraphia is nearly always accompanied by other learning differences such as dyslexia or attention deficit disorder, and this can impact the type of dysgraphia a person might have. There are three principal subtypes of dysgraphia that are recognized. There is little information available about different types of dysgraphia and there are likely more subtypes than the ones listed below. Some children may have a combination of two or more of these, and individual symptoms may vary in presentation from what is described here. Most common presentation is a motor dysgraphia/agraphia resulting from damage to some part of the motor cortex in the parietal lobes.

The word hyperlexia is derived from the Greek terms "hyper" ("over") and "léxis" ("diction", "word").

There are some common problems not related to dysgraphia but often associated with dysgraphia, the most common of which is stress. Often children (and adults) with dysgraphia will become extremely frustrated with the task of writing (and spelling); younger children may cry, pout, or refuse to complete written assignments. This frustration can cause the child (or adult) a great deal of stress and can lead to stress-related illnesses. This can be a result of any symptom of dysgraphia.

Semantic dyslexia is, as the name suggests, a subtype of the group of cognitive disorders known as alexia (acquired dyslexia). Those who suffer from semantic dyslexia are unable to properly attach words to their meanings in reading and/or speech. When confronted with the word "diamond", they may understand it as "sapphire", "shiny" or "diamonds"; when asking for a bus ticket, they may ask for some paper or simply "a thing".

Semantic dementia (SD) is a degenerative disease characterized by atrophy of anterior temporal regions (the primary auditory cortex; process auditory information) and progressive loss of semantic memory. SD patients often present with surface dyslexia, a relatively selective impairment in reading low-frequency words with exceptional or atypical spelling-to-sound correspondences.

Hyperlexia is a syndrome characterized by a child's precocious ability to read. It was initially identified by Norman E. Silberberg and Margaret C. Silberberg (1967), who defined it as the precocious ability to read words without prior training in learning to read, typically before the age of 5. They indicated that children with hyperlexia have a significantly higher word-decoding ability than their reading comprehension levels. Children with hyperlexia also present with an intense fascination for written material at a very early age.

Hyperlexic children are characterized by having average or above-average IQs, and word-reading ability well above what would be expected given their age. First named and scientifically described in 1967 (Silverberg and Silverberg), it can be viewed as a superability in which word recognition ability goes far above expected levels of skill. Some hyperlexics, however, have trouble understanding speech. Some experts believe that most, or perhaps all children with hyperlexia, lie on the autism spectrum. However, one expert, Darold Treffert, proposes that hyperlexia has subtypes, only some of which overlap with autism. Between 5 and 20 percent of autistic children have been estimated to be hyperlexic.

Hyperlexic children are often fascinated by letters or numbers. They are extremely good at decoding language and thus often become very early readers. Some hyperlexic children learn to spell long words (such as "elephant") before they are two years old and learn to read whole sentences before they turn three.

An fMRI study of a single child showed that hyperlexia may be the neurological opposite of dyslexia.

There are two general classifications of amusia: congenital amusia and acquired amusia.

Language-based learning disabilities or LBLD are "heterogeneous" neurological differences that can affect skills such as listening, reasoning, speaking, reading, writing, and maths calculations. It is also associated with movement, coordination, and direct attention. LBLD is not usually identified until the child reaches school age. Most people with this disability find it hard to communicate, to express ideas efficiently and what they say may be ambiguous and hard to understand

It is a neurological difference. It is often hereditary, and is frequently associated to specific language problems.

There are two types of learning disabilities: non-verbal, which includes disabilities from psychomotor difficulties to dyscalculia, and verbal, language based.

Peripheral dyslexias have been described as affecting the visual analysis of letters as a result of brain injury. Hemianopsia, a visual field loss on the left/right side of the vertical midline, is associated with this condition.

A reading disability is a condition in which a sufferer displays difficulty reading resulting primarily from neurological factors. Developmental Dyslexia, Alexia (acquired dyslexia), and Hyperlexia (word-reading ability well above normal for age and IQ).

Central dyslexias include surface dyslexia, semantic dyslexia, phonological dyslexia, and deep dyslexia. ICD-10 reclassified the previous distinction between dyslexia (315.02 in ICD-9) and alexia (315.01 in ICD-9) into a single classification as R48.0. The terms are applied to developmental dyslexia and inherited dyslexia along with developmental aphasia and inherited alexia, which are considered synonymous.

National Institute of Neurological Disorders and Stroke defines reading disability or dyslexia as follows: "Dyslexia is a brain-based type of learning disability that specifically impairs a person's ability to read. These individuals typically read at levels significantly lower than expected despite having normal intelligence. Although the disorder varies from person to person, common characteristics among people with dyslexia are difficulty with spelling, phonological processing (the manipulation of sounds), and/or rapid visual-verbal responding. In adults, dyslexia usually occurs after a brain injury or in the context of dementia. It can also be inherited in some families, and recent studies have identified a number of genes that may predispose an individual to developing dyslexia."

The NINDS definition is not in keeping with the bulk of scientific studies that conclude that there is no evidence to suggest that dyslexia and intelligence are related. The Rose Review 2009 Definition is more in keeping with modern research and debunked discrepancy model of dyslexia diagnosis:

- Dyslexia is a learning difficulty that primarily affects the skills involved in accurate and fluent word reading and spelling.

- Characteristic features of dyslexia are difficulties in phonological awareness, verbal memory and verbal processing speed.

- Dyslexia occurs across the range of intellectual abilities.

- It is best thought of as a continuum, not a distinct category, and there are no clear cut-off points.

- Co-occurring difficulties may be seen in aspects of language, motor co-ordination, mental calculation, concentration and personal organisation, but these are not, by themselves, markers of dyslexia.

- A good indication of the severity and persistence of dyslexic difficulties can be gained by examining how the individual responds or has responded to well founded intervention.

Auditory processing disorder (APD), also known as central auditory processing disorder (CAPD), is an umbrella term for a variety of disorders that affect the way the brain processes auditory information. Individuals with APD usually have normal structure and function of the outer, middle and inner ear (peripheral hearing). However, they cannot process the information they hear in the same way as others do, which leads to difficulties in recognizing and interpreting sounds, especially the sounds composing speech. It is thought that these difficulties arise from dysfunction in the central nervous system.

The American Academy of Audiology notes that APD is diagnosed by difficulties in one or more auditory processes known to reflect the function of the central auditory nervous system.

APD can affect both children and adults, although the actual prevalence is currently unknown. It has been suggested that males are twice as likely to be affected by the disorder as females, but there are no good epidemiological studies.

The National Institute on Deafness and Other Communication Disorders state that children with Auditory Processing Disorder often:

- have trouble paying attention to and remembering information presented orally, and may cope better with visually acquired information

- have problems carrying out multi-step directions given orally; need to hear only one direction at a time

- have poor listening skills

- need more time to process information

- have low academic performance

- have behavior problems

- have language difficulties (e.g., they confuse syllable sequences and have problems developing vocabulary and understanding language)

- have difficulty with reading, comprehension, spelling, and vocabulary

APD can manifest as problems determining the direction of sounds, difficulty perceiving differences between speech sounds and the sequencing of these sounds into meaningful words, confusing similar sounds such as "hat" with "bat", "there" with "where", etc. Fewer words may be perceived than were actually said, as there can be problems detecting the gaps between words, creating the sense that someone is speaking unfamiliar or nonsense words. In addition, it is common for APD to cause speech errors involving the distortion and substitution of consonant sounds. Those suffering from APD may have problems relating what has been said with its meaning, despite obvious recognition that a word has been said, as well as repetition of the word. Background noise, such as the sound of a radio, television or a noisy bar can make it difficult to impossible to understand speech, since spoken words may sound distorted either into irrelevant words or words that don't exist, depending on the severity of the auditory processing disorder. Using a telephone can be problematic for someone with auditory processing disorder, in comparison with someone with normal auditory processing, due to low quality audio, poor signal, intermittent sounds and the chopping of words. Many who have auditory processing disorder subconsciously develop visual coping strategies, such as lip reading, reading body language, and eye contact, to compensate for their auditory deficit, and these coping strategies are not available when using a telephone.

As noted above, the status of APD as a distinct disorder has been queried, especially by speech-language pathologists and psychologists, who note the overlap between clinical profiles of children diagnosed with APD and those with other forms of specific learning disability. Many audiologists, however, would dispute that APD is just an alternative label for dyslexia, SLI, or ADHD, noting that although it often co-occurs with these conditions, it can be found in isolation.

Individuals who suffer from phonological dyslexia have the opposite problem to surface dyslexics. These individuals are able to read using the whole word method. However, they struggle when it comes to sounding words out. Phonological dyslexics are able to read familiar words, but have difficulties when it comes to unfamiliar words or non-words that are pronounceable. Several studies have found that many phonological dyslexics have a good reading ability if the individual has developed a large vocabulary prior to suffering from brain damage. These individuals seem to stop developing their vocabulary post-brain damage, which affects their reading capacity.

Phonological dyslexia is a reading disorder in which the patient has impaired reading of nonwords. The symptoms of phonological dyslexia are very similar to those of deep dyslexia. The major difference between these two dyslexias is that phonological dyslexics do not make semantic errors associated with deep dyslexia. Beauvois and Dérouesné (1979) studied the first case of phonological dyslexia and came up with this term. The problem people with phonological dyslexia have is that they are able to read words using the whole word method; however, they are not able to sound words out. This means that they are able to read familiar words, but have difficulties reading new words.

Initially it was believed that the factor causing phonological dyslexia was lexicality; however, other factors such as imageability and concreteness also play a critical role in reading. A study done by Crisp and Lambon Ralph concluded that imageability has a significant effect on phonological dyslexia. The study found that eleven out of the twelve patients had more accuracy when reading words with high imageability. In that study, the patient who was the exception was the least severely damaged, contributing to a view of phonological dyslexia and deep dyslexia as points on a continuum rather than discrete disorders.

Amusia is a musical disorder that appears mainly as a defect in processing pitch but also encompasses musical memory and recognition. Two main classifications of amusia exist: acquired amusia, which occurs as a result of brain damage, and congenital amusia, which results from a music-processing anomaly present since birth.

Studies have shown that congenital amusia is a deficit in fine-grained pitch discrimination and that 4% of the population suffers from this disorder. Acquired amusia, on the other hand, may take several forms. Patients with brain damage may experience the loss of ability to produce musical sounds while sparing speech, much like aphasics lose speech selectively but can sometimes still sing. Other forms of amusia may affect specific sub-processes of music processing. Current research has demonstrated dissociations between rhythm, melody, and emotional processing of music, and amusia may include impairment of any combination of these skill sets.

The defining characteristic of SD is decreased performance on tasks that require semantic memory. This includes difficulty with naming pictures and objects, single word comprehension, categorizing, and knowing uses and features of objects. SD patients also have difficulty with spontaneous speech creation, using words such as "this" or "things" where more specific and meaningful words can be used. Syntax is spared, and SD patients have the ability to discern syntactic violations and comprehend sentences with minimal lexical demands. SD patients have selectively worse concrete word knowledge and association, but retain knowledge and understanding of abstract words. SD patients are able to retain knowledge of numbers and music, but have more difficulty with concrete concepts with visual associations. Impairments of processing of phonemic structure and prosodic predictability have also been observed.

Semantic dementia (SD), also known as semantic variant primary progressive aphasia (svPPA), is a progressive neurodegenerative disorder characterized by loss of semantic memory in both the verbal and non-verbal domains. However, the most common presenting symptoms are in the verbal domain (with loss of word meaning). SD is one of the three canonical clinical syndromes associated with frontotemporal lobar degeneration (FTLD), with the other two being frontotemporal dementia and progressive nonfluent aphasia. SD is a clinically defined syndrome, but is associated with predominantly temporal lobe atrophy (left greater than right) and hence is sometimes called temporal variant FTLD (tvFTLD). SD is one of the three variants of Primary Progressive Aphasia (PPA), which results from neurodegenerative disorders such as FTLD or Alzheimer's disease. It is important to note the distinctions between Alzheimer’s Disease and Semantic dementia with regard to types of memory affected. In general, Alzheimer’s Disease is referred to as disorder affecting mainly episodic memory, defined as the memory related to specific, personal events distinct for each individual. Semantic dementia generally affects semantic memory, which refers to long-term memory that deals with common knowledge and facts.3

It was first described by Arnold Pick in 1904 and in modern times was characterized by Professor Elizabeth Warrington in 1975, but it was not given the name semantic dementia until 1989. The clinical and neuropsychological features, and their association with temporal lobe atrophy were described by Professor John Hodges and colleagues in 1992.

LBLD consists of dyscalculia which comprises the reading of numbers sequentially, learning the time table, and telling time;

dyslexia; and difficulties associated with written language such as trouble learning new vocabulary, letters and alphabets. Auditory processing disorders can cause trouble understanding questions and following directions, understanding and remembering the details of a story's plot or a classroom lecture, learning words to songs and rhymes, telling left from right, and having a hard time with reading and writing .

Difficulties associated with reading and spoken language involve trouble understanding questions and following directions, understanding and retaining the details of a story's plot or a classroom lecture, nonword repetition, learning words to songs and rhymes, and identifying the sounds that correspond to letters, which makes learning to read difficult

Difficulties associated with motor skills include difficulty telling left from right which is part of motor incoordination, visual perceptual problems, and memory problem

Research on subtypes of dyscalculia has begun without consensus; preliminary research has focused on comorbid learning disorders as subtyping candidates. The most common comorbidity in individuals with dyscalculia is dyslexia. Most studies done with comorbid samples versus dyscalculic-only samples have shown different mechanisms at work and additive effects of comorbidity, indicating that such subtyping may not be helpful in diagnosing dyscalculia. But there is variability in results at present.

Due to high comorbidity with other disabilities such as dyslexia and ADHD, some researchers have suggested the possibility of subtypes of mathematical disabilities with different underlying profiles and causes. Whether a particular subtype is specifically termed "dyscalculia" as opposed to a more general mathematical learning disability is somewhat under debate in the scientific literature.

- Semantic memory: This subtype often coexists with reading disabilities such as dyslexia and is characterized by poor representation and retrieval from long-term memory. These processes share a common neural pathway in the left angular gyrus, which has been shown to be selective in arithmetic fact retrieval strategies and symbolic magnitude judgments. This region also shows low functional connectivity with language-related areas during phonological processing in adults with dyslexia. Thus, disruption to the left angular gyrus can cause both reading impairments and difficulties in calculation. This has been observed in individuals with Gerstmann syndrome, of which dyscalculia is one of constellation of symptoms.

- Procedural concepts: Research by Geary has shown that in addition to increased problems with fact retrieval, children with math disabilities may rely on immature computational strategies. Specifically, children with mathematical disabilities showed poor command of counting strategies unrelated to their ability to retrieve numeric facts. This research notes that it is difficult to discern whether poor conceptual knowledge is indicative of a qualitative deficit in number processing or simply a delay in typical mathematical development.

- Working memory: Studies have found that children with dyscalculia showed impaired performance on working memory tasks compared to neurotypical children. Furthermore, research has shown that children with dyscalculia have weaker activation of the intraparietal sulcus during visuospatial working memory tasks. Brain activity in this region during such tasks has been linked to overall arithmetic performance, indicating that numerical and working memory functions may converge in the intraparietal sulcus. However, working memory problems are confounded with domain-general learning difficulties, thus these deficits may not be specific to dyscalculia but rather may reflect a greater learning deficit. Dysfunction in prefrontal regions may also lead to deficits in working memory and other executive function, accounting for comorbidity with ADHD.

Studies have also shown indications of causes due to congenital or hereditary disorders, but evidence of this is not yet concrete.