It's an issue of 'mental energy' and how you use it. If you are performing at capacity, and try and do two things at once, you'll perform below standard on the second task.

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This can seem like some age-related memory problem like mild cognitive impairment or Alzheimer's, but it's really a sensory problem.

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There are subtle effects of hearing loss on memory and cognitive function in older adults. The effect of expending extra effort comprehending words means there are fewer cognitive resources for higher level comprehension.

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