Understanding Alexia and Agraphia in Communication Disorders

Alexia

acquired reading disorder (impacting oral reading and/or reading comprehension)

Agraphia

acquired writing disorder

Grapheme

smallest unit that signals a difference in meaning in a writing system (e.g., "p", "sh", "ch", "i")

Allograph

variations of a grapheme

Case

upper vs. lower

Print type

cursive vs. print

Pseudoword

not a word in the language, but follows phonological rules (e.g., for English "blaf")

Cognitive architecture

mental operations involved in a brain function

Peripheral alexia

affects earlier processing stages of reading; difficulty visually perceiving written word

Central alexia

affects later processing stages of reading; difficulty attaching sound or meaning to written word

Pure alexia

impairment in the simultaneous, parallel identification and processing of letters in a written word

Neglect alexia

Impairment in correctly identifying initial or final letters in words

Attentional alexia

incorrect productions of letters in a word as a result of interference from other letters in the word

Visual alexia

production of a word that is visually similar to the target word

Surface alexia

a type of central alexia

Phonological alexia

a type of central alexia

Deep alexia

a type of central alexia

Alexia without agraphia

significant reading impairment without significant writing impairment (rare)

Lesion site for Pure alexia

Left occipital cortex and splenium of corpus callosum

Lesion site for Neglect alexia

Visual processing areas (variable)

Lesion site for Attentional alexia

Visual processing areas (variable)

Lesion site for Visual alexia

Visual processing areas (variable)

Surface alexia

Impaired lexical reading with impaired oral reading of irregularly spelled words (e.g., "yacht"), relatively intact reading of regularly spelled words (e.g., "bat") and pseudowords, and regularization errors due to over-reliance on nonlexical reading route.

Phonological alexia

Impaired nonlexical reading characterized by impaired pseudoword reading, lexicalization errors (e.g., blaf -> black), and absence of semantic errors in oral reading.

Deep alexia

Impaired lexical and non-lexical reading with impaired oral reading of pseudowords (e.g., blaf), semantic, visual, and morphological errors in oral reading, and easier reading of concrete, imageable words.

Central alexias

Types of alexia that involve impairments in the central processes of reading.

Lesion site for Surface alexia

Left temporal / temporo-parietal (variable).

Lesion site for Phonological alexia

Left perisylvian, left superior temporal cortex (variable).

Lesion site for Deep alexia

Extensive left hemisphere lesion.

Lexical writing route

Accesses word forms and generates spelling for familiar word forms.

Lexical semantic route

Accesses the semantic system needed for written confrontation naming.

Lexical nonsemantic route

Bypasses the semantic system.

Nonlexical writing route

Does not access word forms and is used to process words not in spelling vocabulary.

Peripheral agraphia

Impairment of peripheral processes that convert graphemes into motor commands for writing.

Central agraphia

Impairment of central linguistic processes that generate spellings for words and pseudowords.

Allographic agraphia

Impairment in generating or selecting correct letter shapes in handwriting, with oral spelling spared.

Apraxic agraphia

Impairment related to the motor planning of writing.

Motor nonapraxic agraphia

Impairment in writing that is not due to apraxia.

Spatial / afferent agraphia

Impairment affecting the spatial aspects of writing.

Mixed writing profiles

Commonly observed in individuals with various types of agraphia.

Lesion site for Allographic agraphia

Left parieto-occipital cortex.

Apraxic agraphia

Poor letter formation not attributed to impaired letter shape knowledge or to sensorimotor, extrapyramidal, or cerebellar dysfunction affecting writing hand.

Oral spelling, typing, and anagram tasks

Preserved in apraxic agraphia.

Motor nonapraxic agraphia

Impairment in regulating movement force, speed, and amplitude in handwriting.

Micrographia

Example of motor nonapraxic agraphia seen in Parkinson's disease.

Spatial / afferent agraphia

Impaired ability to use sensory feedback for control and execution of writing.

Common errors in spatial / afferent agraphia

Duplications or omissions of letters or strokes, difficulty keeping line of writing straight, difficulty maintaining spacing between letters and words.

Surface / lexical agraphia

Impaired lexical writing / spelling with over-reliance on non-lexical route.

Phonological agraphia

Impaired nonlexical writing/spelling with over-reliance on lexical route.

Deep agraphia

Impaired lexical and nonlexical writing / spelling with similar errors as phonological agraphia plus semantic errors.

Semantic agraphia

Impairment of conceptually mediated writing tasks, with relatively spared writing to dictation.

Graphemic output buffer impairment

Impaired short-term storage of graphemic information leading to errors with grapheme order and identity in all spelling tasks.

Narrative writing sample - Broca's aphasia

Task: Written picture description.

Narrative writing sample - Wernicke's aphasia

Task: Written picture description.

Narrative writing sample - conduction aphasia

Task: Written picture description.

Functional reading and writing

Reading and writing impairment impact everyday functioning.

Examples of functional reading and writing

Reading newspapers, magazines, books, environmental signs, prescriptions, recipes, and other instructions.

Terminology: alexia, agraphia, grapheme, allograph, pseudoword

Key terms related to reading and writing impairments.

Dual route model of reading

A model describing the processes involved in reading.

Neuropsychological model of writing

A model describing the processes involved in writing.

Central vs. peripheral agraphia

Classification of agraphia based on underlying cognitive processes.

Relationships between reading, writing, and speaking

Understanding how these skills interact and affect communication.

Communication and participation implications of alexia and agraphia

Impact of reading and writing impairments on daily life and social interactions.