This is a common complaint when people go to a busy restaurant with lots of ambient noise.  Perhaps they go with a group of people to a crowded restaurant.  As the noise in the restaurant escalates, it becomes increasingly more difficult to follow the conversation at the table.  At the same time, noises such as speech babble and dishes are easy to detect.

Detecting the presence of sound is an easy task for the human brain.  It requires very little processing or concentration.  During a hearing test, even those with dementia provide reliable results by pushing the button when a tone is heard.  Repeating a list of words is a much more difficult task for the human brain, as it requires the listener to concentrate and accurately interpret what is being said.  Even in a quiet room this requires active listening.  The ability to repeat the words accurately are affected by the speaker’s rate of speech, their articulation, and the pitch of their voice.  Listener concentration and fatigue also affect the results.

When people say that they can’t hear in a restaurant, what they are usually saying is that they cannot decipher speech in the presence of so much background noise.  Do hearing aids help?  Absolutely.  Hearing aids employ technology that can cancel out steady state noise and amplify speech coming from specific directions (usually in front of the listener).  They also amplify certain frequencies for improved speech clarity.  Remote microphones increase the speech above the noise for improved hearing in noise.  These features of hearing aids help the brain to block out unnecessary noise so that it can attend to speech.