Speech perception
Agnosia is "the loss or diminution of the ability to recognize familiar objects or stimuli usually as a result of brain damage". There are several different kinds of agnosia that affect every one of our senses, but the two most common related to speech are speech agnosia and phonagnosia.
Associative visual agnosia
Visual object agnosia (or semantic agnosia) is the most commonly encountered form of agnosia. The clinical "definition" of the disorder is when an affected person is able to copy/draw things that they cannot recognize. Individuals afflicted with the associative type often cannot identify, describe or mimic functions of items, though perception is intact, since images of objects can be copied or drawn. Individuals may retain semantic knowledge of the items, as exemplified during tasks where objects are presented through alternate modalities, through touch or verbal naming or description. Some associative visual object agnostics retain the ability to categorize items by context or general category, though unable to name or describe them. Diffuse hypoxic damage is the most common cause of visual object agnosias.