Auditory agnosia

Auditory agnosia is a form of agnosia that manifests itself primarily in the inability to recognize or differentiate between sounds. It is not a defect of the ear or "hearing", but a neurological inability of the brain to process sound meaning. It is a disruption of the "what" pathway in the brain. Persons with auditory agnosia can physically hear the sounds and describe them using unrelated terms, but are unable to recognize them. They might describe the sound of some environmental sounds, such as a motor starting, as resembling a lion roaring, but would not be able to associate the sound with "car" or "engine", nor would they say that it was a lion creating the noise. Auditory agnosia is caused by damage to the secondary and tertiary auditory cortex of the temporal lobe of the brain.

There are three primary distinctions of auditory agnosia that fall into two categories.

This type of auditory agnosia is caused by lesions to the left hemisphere of the brain, specifically the temporal lobes and Wernicke's area.

Linguistic (or verbal information or Wernicke's) agnosia indicates that the subject can't comprehend words, although they can understand words using sign language and words from reading books, and are themselves capable of speech (and even of deriving meaning from non-linguistic communication e.g. body language) the particular sounds associated to each word are meaningless.

This type of auditory agnosia is caused by lesions to the right hemisphere of the brain.

Classical (or pure) auditory agnosia is an inability to process environmental sounds, such as animal noises, industrial noises, or the like. An airplane roaring overhead would not be understood to be related to the idea of "airplane"—indeed, the person would not even think to look up.

Interpretive or receptive agnosia (amusia) is an inability to understand music. The term "amusia" covers a broad spectrum: from those with a mere deficit of rhythmic ability (mild dysrhythmia), to those with heavy all-encompassing amusia, including the recently coined "distimbria"; sufferers regard music as simply "noise", often compared to drainpipes or drills, or other invasive forms of background noise. Vocal singing can be understood, but is simply seen as "odd tone of voice". The standard is considered to be that amusics with a "normal" intensity of amusia are cortically unable to distinguish pitch changes of less than three semitones (when it includes a pitch-deficit; it is contentious whether without this symptom it can be considered amusia). They may appreciate or enjoy listening to or performing music, but some can not tolerate it or find it irritating.

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