[2] Persons with auditory agnosia can physically hear the sounds and describe them using unrelated terms, but are unable to recognize them.
Typically, a person with auditory agnosia would be incapable of comprehending spoken language as well as environmental sounds.
A relationship between hearing and the brain was first documented by Ambroise Paré, a 16th century battlefield doctor, who associated parietal lobe damage with acquired deafness (reported in Henschen, 1918[8]).
Wernicke proposed that the impaired perception of language in his patients was due to losing the ability to register sound frequencies that are specific to spoken words (he also suggested that other aphasic symptoms, such as speaking, reading and writing errors occur because these speech specific frequencies are required for feedback).
Wernicke localized the perception of spoken words to the posterior half of the left STG (superior temporal gyrus).
This case-study led Kussmaul to propose of distinction between the word perception deficit and Wernicke's sensory aphasia.
This argument, however, was refuted by Bonvicini[15] (1905), who measured the hearing of an auditory agnosia patient with tuning forks, and confirmed intact pure tone perception.
Similarly, Barrett's aphasic patient,[16] who was incapable of comprehending speech, had intact hearing thresholds when examined with tuning forks and with a Galton whistle.
The most adverse opponent to the model of Wernicke and Lichtheim was Marie[17] (1906), who argued that all aphasic symptoms manifest because of a single lesion to the language reception center, and that other symptoms such as auditory disturbances or paraphasia are expressed because the lesion encompasses also sub-cortical motor or sensory regions.
Geschwind interpreted this asymmetry as anatomical verification for the role of left posterior STG in the perception of language.
Although some researchers argued against the purity of word deafness, some anecdotal cases with exclusive impaired perception of speech were documented.
[44][45] In a review of the auditory agnosia literature, Phillips and Farmer[46] 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.
Pinard et al[43] also suggested that pure word deafness and general auditory agnosia represent different degrees of the same disorder.
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).
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.
[48] The term auditory agnosia was originally coined by Sigmund Freud[13] in 1891, to describe patients with selective impairment of environmental sounds.
[59][60] A possible neuroanatomical structure that relays longer sound duration was suggested by Tanaka et al.[24] By comparing the lesions of two cortically deaf patients with the lesion of a word deafness patient, they proposed the existence of two thalamocortical pathways that inter-connect the MGN with the auditory cortex.
[62] The medical literature reports of 33 patients diagnosed with an exclusive deficit for the discrimination and recognition of musical segments[7] (i.e., amusia).
[65] These findings therefore imply that the loss of music perception in auditory agnosia is because of damage to the medial anterior STG.
Although the conclusion reached by this study could be considered over-reaching, associative auditory agnosia could correspond with the disorder word meaning deafness.
In the first documented case,[76] Bramwell (1897 - translated by Ellis, 1984) reported a patient, who in order to comprehend speech wrote what she heard and then read her own handwriting.
[85][86] Word meaning deafness is also often confused with transcortical sensory aphasia, but such patients differ from the latter by their ability to express themselves appropriately orally or in writing.
A rare insight into the etiology of this disorder was reported in a study of an auditory agnosia patient with damage to the brainstem, instead of cortex.
These brain areas are part of the auditory 'what' pathway, and are known from both human and monkey research to participate in the recognition of sounds.