The Trusted Advisor blog identified the phenomenon when writer Charles H. Green went for a hearing test. His hearing was fine - but his examiner pointed out that she'd tested a lot of people lately who thought they had a hearing problem, but didn't.

She said:

"What's happening is that these people have lost the ability to pay attention for more than a few seconds. When the conversation requires more attention, they zone out, and lose connection.

"When they zip back, a nano-second later, they realise they've missed something. And they blame their hearing. It's not their hearing, it’s their multi-tasking."