The cocktail party effect refers to the phenomenon wherein the brain focuses a person's attention on a particular stimulus, usually auditory. This focus excludes a range of other stimuli from conscious awareness, as when a partygoer follows a single conversation in a noisy room. This ability is widely distributed among humans, with most listeners more or less easily able to portion the totality of sound detected by the ears into distinct streams, and subsequently to decide which streams are most pertinent, excluding all or most others.
It has been proposed that a person's sensory memory subconsciously parses all stimuli and identifies discrete portions of these sensations according to their salience. This allows most people to tune effortlessly into a single voice while tuning out all others. The phenomenon is often described as a "selective attention" or "selective hearing". It may also describe a similar phenomenon that occurs when one may immediately detect words of importance originating from unattended stimuli, for instance hearing one's name among a wide range of auditory input.
A person who lacks the ability to segregate stimuli in this way is often said to display the cocktail party problem or cocktail party deafness. This may also be described as auditory processing disorder or King-Kopetzky syndrome.
Neurological basis (and binaural processing) Auditory attention in regards to the cocktail party effect primarily occurs in the left hemisphere of the superior temporal gyrus, a non-primary region of auditory cortex; a fronto-parietal network involving the inferior frontal gyrus, superior parietal sulcus, and intraparietal sulcus also accounts for the acts of attention-shifting, speech processing, and attention control. Both the target stream (the more important information being attended to) and competing/interfering streams are processed in the same pathway within the left hemisphere, but fMRI scans show that target streams are treated with more attention than competing streams.
Furthermore, activity in the superior temporal gyrus (STG) toward the target stream is decreased/interfered with when competing stimuli streams (that typically hold significant value) arise. The "cocktail party effect" – the ability to detect significant stimuli in multi-talker situations – has also been labeled the "cocktail party problem", because the ability to selectively attend simultaneously interferes with the effectiveness of attention at a neurological level.
The cocktail party effect works best as a binaural effect, which requires hearing with both ears. People with only one functioning ear seem much more distracted by interfering noise than people with two typical ears. The benefit of using two ears may be partially related to the localization of sound sources. The auditory system is able to localize at least two sound sources and assign the correct characteristics to these sources simultaneously. As soon as the auditory system has localized a sound source, it can extract the signals of this sound source out of a mixture of interfering sound sources. However, much of this binaural benefit can be attributed to two other processes, better-ear listening and binaural unmasking. Better-ear listening is the process of exploiting the better of the two signal-to-noise ratios available at the ears. Binaural unmasking is a process that involves a combination of information from the two ears in order to extract signals from noise.
Early work
In the early 1950s much of the early attention research can be traced to problems faced by air traffic controllers. At that time, controllers received messages from pilots over loudspeakers in the control tower. Hearing the intermixed voices of many pilots over a single loudspeaker made the controller's task very difficult. The effect was first defined and named "the cocktail party problem" by Colin Cherry in 1953. Cherry conducted attention experiments in which participants listened to two different messages from a single loudspeaker at the same time and tried to separate them; this was later termed a dichotic listening task. His work reveals that the ability to separate sounds from background noise is affected by many variables, such as the sex of the speaker, the direction from which the sound is coming, the pitch, and the rate of speech.