In which type of aphasia is spontaneous speech preserved but auditory comprehension is impaired?

Wernicke's aphasia is characterized by fluent but often nonsensical speech, where the individual can produce speech with normal grammar and syntax but has significant deficits in auditory comprehension. This means that while a person with Wernicke's aphasia can speak freely, their understanding of language is profoundly affected, leading to difficulty following conversations or comprehending spoken language.

In contrast, Broca's aphasia typically involves non-fluent speech with good comprehension, where individuals struggle to find words and form sentences but can often understand what is being said to them. Global aphasia presents with extensive language impairment in both expressive and receptive modalities, making it much more severe than Wernicke's. Mixed non-fluent aphasia, like Broca's, involves reduced spontaneous speech and better comprehension compared to Wernicke's.

Thus, Wernicke's aphasia is distinguished by the preservation of spontaneous speech alongside significant impairments in auditory comprehension, making it the correct answer to the question.