Cocktail party effect

When they are in a noisy environment, humans have the ability to focus their hearing onto one source. This phenomenon is called cocktail party effect. It is named after the fact that a person attending a noisy cocktail party is able to focus their listening to the conversation they are doing, and disregard the other conversations. 
It has been proposed that one's sensory memory subconsciously parses all stimuli and identifies discrete pieces of information by classifying them by salience. This effect is what allows most people to "tune into" a single voice and "tune out" all others. This phenomenon is often described in terms of "selective attention" or "selective hearing". It may also describe a similar phenomenon that occurs when one may immediately detect words of importance coming from unattended stimuli, for example hearing one's name among a wide range of auditory input.
An inability to segregate stimuli in this way is sometimes referred to as the cocktail party problem or cocktail party deafness.