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| title | chunk | source | category | tags | date_saved | instance |
|---|---|---|---|---|---|---|
| Auditory agnosia | 3/5 | https://en.wikipedia.org/wiki/Auditory_agnosia | reference | science, encyclopedia | 2026-05-05T07:26:21.081452+00:00 | kb-cron |
=== Cerebral deafness === Cerebral deafness (also known as cortical deafness or central deafness) is a disorder characterized by complete deafness that is the result of damage to the central nervous system. The primary distinction between auditory agnosia and cerebral deafness is the ability to detect pure tones, as measured with pure tone audiometry. Using this test, auditory agnosia patients were often reported capable of detecting pure tones almost as good as healthy individuals, whereas cerebral deafness patients found this task almost impossible or they required very loud presentations of sounds (above 100 dB). In all reported cases, cerebral deafness was associated with bilateral temporal lobe lesions. A study that compared the lesions of two cerebral deafness patients to an auditory agnosia patient concluded that cerebral deafness is the result of complete de-afferentation of the auditory cortices, whereas in auditory agnosia some thalamo-cortical fibers are spared. In most cases the disorder is transient and the symptoms mitigate into auditory agnosia (although chronic cases were reported). Similarly, a monkey study that ablated both auditory cortices of monkeys reported of deafness that lasted 1 week in all cases, and that was gradually mitigated into auditory agnosia in a period of 3–7 weeks.
=== Pure word deafness === Since the early days of aphasia research, the relationship between auditory agnosia and speech perception has been debated. Lichtheim (1885) proposed that auditory agnosia is the result of damage to a brain area dedicated to the perception of spoken words, and consequently renamed this disorder from 'word deafness' to 'pure word deafness'. The description of word deafness as being exclusively for words was adopted by the scientific community despite the patient reported by Lichtheim's who also had more general auditory deficits. Some researchers who surveyed the literature, however, argued against labeling this disorder as pure word deafness on the account that all patients reported impaired at perceiving spoken words were also noted with other auditory deficits or aphasic symptoms. In one review of the literature, Ulrich (1978) presented evidence for separation of word deafness from more general auditory agnosia, and suggested naming this disorder "linguistic auditory agnosia" (this name was later rephrased into "verbal auditory agnosia"). To contrast this disorder with auditory agnosia in which speech repetition is intact (word meaning deafness), the name "word sound deafness" and "phonemic deafness" (Kleist, 1962) were also proposed. Although some researchers argued against the purity of word deafness, some anecdotal cases with exclusive impaired perception of speech were documented. On several occasions, patients were reported to gradually transition from pure word deafness to general auditory agnosia/cerebral deafness or recovery from general auditory agnosia/cerebral deafness to pure word deafness. In a review of the auditory agnosia literature, Phillips and Farmer showed that patients with word deafness are impaired in their ability to discriminate gaps between click sounds as long as 15-50 milliseconds, which is consistent with the duration of phonemes. They also showed that patients with general auditory agnosia are impaired in their ability to discriminate gaps between click sounds as long as 100–300 milliseconds. The authors further showed that word deafness patients liken their auditory experience to hearing foreign language, whereas general auditory agnosia described speech as incomprehensible noise. Based on these findings, and because both word deafness and general auditory agnosia patients were reported to have very similar neuroanatomical damage (bilateral damage to the auditory cortices), the authors concluded that word deafness and general auditory agnosia is the same disorder, but with a different degree of severity. Pinard et al also suggested that pure word deafness and general auditory agnosia represent different degrees of the same disorder. They suggested that environmental sounds are spared in the mild cases because they are easier to perceive than speech parts. They argued that environmental sounds are more distinct than speech sounds because they are more varied in their duration and loudness. They also proposed that environmental sounds are easier to perceive because they are composed of a repetitive pattern (e.g., the bark of a dog or the siren of the ambulance). Auerbach et al considered word deafness and general auditory agnosia as two separate disorders, and labelled general auditory agnosia as pre-phonemic auditory agnosia and word deafness as post-phonemic auditory agnosia. They suggested that pre-phonemic auditory agnosia manifests because of general damage to the auditory cortex of both hemispheres, and that post-phonemic auditory agnosia manifests because of damage to a spoken word recognition center in the left hemisphere. A recent research on an epileptic patient supported this hypothesis. The patient undergone electro-stimulation to the anterior superior temporal gyrus, and demonstrated a transient loss of speech comprehension, while preserving intact perception of environmental sounds and music.