are closely spaced in time. Note that this is not unique to speech; studies using non-speech sounds closely spaced in time (dog bark, phone ring, lightning, etc.) have shown that those with auditory verbal agnosia are unable to discriminate between those sounds in the majority of cases, though a few putative examples of speech-specific impairment have been documented in the literature. Neurological deficits Auditory verbal agnosia is caused by bilateral damage, often in the form of cerebrovascular accidents which form as a result of an embolism, to the posterior superior temporal lobes or disruption of connections between these areas. A unilateral lesion in the left or right superior temporal lobe can also result in pure word deafness, this being much more common in the left hemisphere than the right. It is often associated with lesions to the left posterior superior temporal lobe, but no such unilateral case has yet been documented without damage to the white matter tract connecting superior temporal lobes bilaterally or bilateral damage to the superior temporal lobe. In cases where unilateral damage to the left superior temporal lobe has been documented, patients exhibited problems processing both speech and non-speech sounds (in other words, not typical of auditory verbal agnosia). These facts, in combination with the existence of cases of damage to these white matter tracts without detectable cortical damage, in combination with cases of pure word deafness resulting enlargement of the third ventricle alone suggest that the disorder results from damage to the left-right superior temporal circuit rather than the superior temporal area on one hemisphere or the other. Many of the bilateral cases share one essential feature: after the first (unilateral) lesion, speech perception was typically intact after an initial period of disturbance. Only after the second lesion (in the other hemisphere) were permanent speech perception problems the consistent outcome. The fact that most of these patients only manifested auditory verbal agnosia subsequent to the second lesion supports the hypothesis that both sides of the superior temporal gyrus are necessary. Auditory verbal agnosia is rarely diagnosed in its pure form. Auditory verbal agnosia can present as the result of acute damage or chronic, progressive degeneration over time. Cases have been documented that result from severe acute head trauma resulting in bilateral temporal lobe damage. In contrast, auditory verbal agnosia has also been documented to present progressively over several years. In one such case, the patient