Final answer:
Wernicke's aphasia is characterized by a receptive language disorder with fluent but meaningless speech, while transcortical sensory aphasia includes fluent speech with comprehension issues but preserved repetition ability, both due to brain damage in language processing areas.
Step-by-step explanation:
The defining feature of Wernicke's aphasia is a receptive language disorder where individuals have difficulties understanding language and may speak in long sentences that lack meaning, use unnecessary words, and have trouble understanding speech. In contrast, transcortical sensory aphasia is similar to Wernicke's in that patients have fluent speech and comprehension issues, but they can repeat words and phrases. Both forms of aphasia are associated with damage to specific regions in the brain that are involved in language comprehension and processing. Wernicke's area, adjacent to the auditory association cortex, is critical for language comprehension, and when damaged, it leads to Wernicke's aphasia. The defining feature of transcortical sensory aphasia, which is less common, is often related to the isolation of the language area from other brain regions responsible for processing sensory input but retains the ability to repeat words and phrases due to intact connections between Wernicke's area and the motor speech area.