I can usually make sense of my kitchen radio, even if someone else is talking or the phone is ringing. This isolation of a single noise among others is known as the 鈥渃ocktail party effect鈥�. However, just crumpling the bag inside a cereal packet renders any other sound unintelligible. Why?
鈥� The term 鈥渃ocktail party effect鈥� was coined by British cognitive scientist Colin Cherry in 1953, although his research was actually prompted by the difficulty air traffic controllers had in keeping track of certain pilots when all their voices were broadcast over a single loudspeaker. Researchers wanted to know how people could tune into a single voice and what prompted their attention to switch to another voice.
While focusing on one source of sound, like someone speaking to you, other conversations form part of the 鈥渦nattended stream鈥�, which is being unconsciously interrogated for any meaningful patterns. If such a pattern is recognised in that stream 鈥� such as your name 鈥� your attention switches.
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You can think of attention as being like computer bandwidth. A person鈥檚 attention (or bandwidth) is increased if they are interested in the conversation (or signal). However, some of this bandwidth is 鈥渘oise鈥�, reducing what is available for the signal. When the noise isn鈥檛 continuous, such as when other conversations are taking place, we can fill in the missing bits of the conversation.
Crumpling a cereal bag is similar to white noise, which is continuous and extends across all frequencies, making it impossible to 鈥渇ill in鈥� the missing snippets on the radio.
The ability to separate sounds from background noise varies according to the rate of speaking and the pitch of the sound, which can depend on the speaker鈥檚 sex. Apparently, the cocktail party effect is enhanced if you can localise the source, which requires both ears, but this ability declines with age.
Mike Follows, Sutton Coldfield, West Midlands, UK
鈥� Recognising a spoken word frequently depends on its initial sound, which is over in a fraction of a second and is usually spoken at a softer and higher pitch than the rest of the word. Try saying any word with the first letter missing to get an idea of how unidentifiable many become without this initial clue.
People like me who have lost much of their higher frequency hearing have no trouble understanding companions in a quiet situation, but are lost in a crowded one. We can hear that our friends are speaking, but we can鈥檛 understand what they are saying because we can no longer hear the beginning of their words above the background noise.
Your questioner obviously hasn鈥檛 lost their higher pitch hearing, so can isolate one voice among many. A telephone ring is different enough from the subtle beginning of words that it causes no problem. But to some extent, the crumpling of a cereal packet mimics these initial word sounds, rendering speech unintelligible. Your questioner is, in fact, having a sneak preview of what life may be like should they ever lose their higher frequency hearing.
Geoffrey Cox, Rotorua, New Zealand
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