Decreased hearing can result from many causes. It is most commonly secondary to inflammation in the upper respiratory tract affecting the Eustachian tube and can be associated with balance problems interfering with psychophysical testing in these circumstances.
It can also effect psychophysical testing by causing confusion in responding to oral instructions. It would exacerbate the confusion associated with Miranda warnings in close temporal proximity to the reading of “Paragraph 36″. Such confusion eliminates the requisite knowledge to form an informed decision.
{Psychophysicals and Refusal}