Mental Acuity: Mental acuity is sharpness of the mind. Things considered in determining a person's mental acuity are memory, focus, concentration, and understanding. An elderly person with Alzheimer's has decreasing mental acuity. He is less likely to remember exactly how or when something happened than he was in his youth. He may also be slow to understand how to do something that seems simple, like operate a television remote control. Many scientists believe there are things you can do to improve mental acuity, such as mental puzzles or other things that actively engage your mind. The popular pasttime of watching TV is passive and would not increase mental acuity, and may actually decrease it.