A 78 year old female has difficulty understanding conversati…

A 78 year old female has difficulty understanding conversations in noisy environments.  She is referred for audiology evaluation.  Audiometry results are as follows:  1)  mild hearing loss at low frequencies, sloping to profound loss at high frequencies; 2) hearing thresholds for air and bone conduction overlap; 3) speech discrimination 83% right in right ear, 85% in left ear. Which of the following is the most likely cause of this patient’s hearing loss?