They may be in the room but they are looking away, changing the subject, uncomfortable. Often the distractor needs a stronger person to lean on and to structure things. Reassurance comes in many different forms. If you are physically present with the person, eye contact and a non-judgmental reflection of what has been said is often enough. This is tricky.
Denial is a big concern.
We often hear that a family member is in denial, and won't go for testing. Denial is a psychological defense mechanism, an unconscious mechanism that by definition is not privy to the person who is using it. Denial is not conscious. In fact these individuals may be unaware, unmotivated, or distracted. Through education, therapy, constructive confrontation, and a variety of life experiences, people can break through the denial process.