Thought & Speech › Aphasia › Receptive Aphasia

Visual Asymbolia

Visual asymbolia is a disorganisation of the brain's visual word processing, such that words cannot be recognised and the motor patterns needed to read them aloud cannot be triggered, even though the person can often still understand words or sentences that are read to them, or that they hear spoken. It is generally associated with a more extensive lesion than the other receptive aphasias, and so is often accompanied by additional neurological findings.

This has traditionally been attributed to lesions involving the angular and supramarginal gyri, and because the underlying lesion tends to be more extensive, it is frequently associated with a cluster of other findings, including difficulty using numbers (acalculia), spatial disorientation, difficulty recognising objects visually, difficulty naming objects, and a specific visual field loss.

Also known as

Cortical visual aphasia

An alternative name for the same condition.

Recognition features

• Difficulty reading words aloud or recognising them visually, though understanding of the same words when heard is often preserved
• Some capacity to copy writing is typically retained, distinguishing this from agnostic alexia
• Difficulty writing spontaneously, even though copying remains possible
• Often accompanied by additional findings such as difficulty with numbers, spatial disorientation, and difficulty naming objects, reflecting the more extensive underlying lesion

Eliciting it at interview

• Test reading aloud, reading comprehension, and listening comprehension separately, since a pattern of preserved listening comprehension despite failed reading is characteristic
• Ask the person to copy a short piece of text as well as to write spontaneously, since copying is typically better preserved than spontaneous writing
• Screen for the associated features specifically — simple calculation, right/left orientation, naming of objects, and visual fields — given how often they co-occur with this condition

Distinguishing features

• Differs from agnostic alexia in that some capacity to copy writing is retained here, whereas it is characteristically lost in agnostic alexia
• Differs from pure word deafness in affecting written rather than spoken language recognition
• The frequent co-occurrence of acalculia, spatial disorientation, and other neurological findings distinguishes this from the more isolated presentations of the other receptive aphasias, reflecting its typically larger underlying lesion

Common misconceptions

• That visual asymbolia is simply a more severe form of agnostic alexia; the two are distinguished by specific, distinct patterns of what is and is not preserved, not merely by degree
• That the accompanying findings (such as difficulty with numbers or spatial orientation) are unrelated coincidences; they commonly reflect the same underlying, more extensive lesion

Related phenomena

Receptive Aphasia · Agnostic Alexia · Gerstmann Syndrome

Practice this

A patient cannot read words aloud or recognise them visually, though he understands the same words perfectly well when they are read to him, and he is still able to copy the written words onto a fresh sheet of paper even though he cannot read what he has copied. What is this? · A patient can see and describe the shapes of the letters on a page perfectly clearly, but cannot make sense of them as written language, and when asked to copy the same words onto another sheet, he is unable to reproduce them at all. Before revealing the answer: is this visual asymbolia? · A patient shows a specific pattern of language comprehension disturbance. Before revealing the answer, decide what distinguishes pure word deafness from visual asymbolia. · A patient cannot read written words despite intact vision. Before revealing the answer, decide what distinguishes visual asymbolia from agnostic alexia. · You suspect a patient has visual asymbolia. Before revealing the answer, decide how you would assess for this. · Explain why visual asymbolia is typically accompanied by additional neurological findings beyond the reading difficulty itself.

Illustration

A 71-year-old woman following an extensive parietal lobe injury cannot read aloud a simple sentence and struggles to recognise the words visually, yet understands the same sentence perfectly well when it is read to her, can copy the words onto a fresh page with reasonable accuracy, and separately has difficulty telling her left hand from her right when asked.

References

• Casey, P. & Kelly, B. (2019). Fish's Clinical Psychopathology, 4th ed. Ch. 4, 'Disorders of Thought and Speech'.