Hearing plays a special role in remembering because we rely primarily on the spoken word for communicating with each other. Specialized memory systems for sounds have evolved in the brain, enabling us to recognize and respond to different sounds.
Sounds such as brass bands, school bells, or the echoing shouts in a swimming pool have a surprising power to take us back to a different time and place. Music is also a startlingly effective trigger for memories – be it a special song that recaptures the early years of a romance or the opening chord of a Rolling Scone crack that entices people to the dance floor and erases a decade of acquired decorum.
Response to music is partly instinctual. There is some evidence that those spine tingling riffs that affect nearly everyone mimic the sounds used by animals to convey emotional messages such as affection, loss, and danger. Complex Melodie. However, have to be learned before they have an effect – hence the constant repetition of certain bars and choruses in most forms of popular music.
Hearing, like every other sensation, is produced by a particular neural firing pattern. Once a tune is learned, we can replay it – albeit faintly – in our heads by re-creating the neuronal pattern produced when we last heard it played. The neurons (nerve cells) that respond to sound are situated mainly in the temporal cortex – the area of the brain above and behind the ears. Those in the brain’s left hemisphere respond selectively to speech, while those on the right register melody and tone. In addition to the neurons that produce conscious hearing, cells in the limbic system (the primitive, unconscious area deep within the brain) produce an emotional reaction to sound, such as fear or delight.
Learning your name
When someone calls your name, the sound triggers several different types of recognition – each one a form of memory. You recognize the word and that it refers to you. You recognize and interpret the tone, whether it is anxious, urgent, or warm. And you may recognize the voice and connect it to a person. Each element of the message contained in that small sound is encoded in a different part of the brain’s memory system.
Just like any other form of knowledge, sounds have to be learned before their full meaning can be recognized. A baby learns the special relevance of its name by hearing it repeatedly, but repetition alone is not enough to give a word meaning. The word becomes distinguished from other sounds by a context that implies some special personal connection. Parents use the name they tend to their baby’s needs and engage in eye contact, causing the child’s sense of self to be activated at the same time as the sound of the name – and the two concepts gradually come to be linked permanently.
Learning the voices that belong to particular people occurs in much the same way. You hear the sound of the voice at the same time as you experience other aspects of the person, such as appearance and details of who they are. Once these links have been made, the mere sound of the voice is enough to hook out memories of the rest of the person. Voice recognition is generally reliable because the characteristic ‘music’ of a voice remains similar whether it is loud or soft, at a distance or dose up.
Echoic memory and the phonological loop
The brain’s briefest memory for sounds is echoic memory – an instant replay that enables us to keep a short string of sounds ‘ on hold’ for a few moments. Fleeting as it is, this type of memory is much in use in some professions: a mechanic listening for a particular knocking noise above the background hum of a car engine uses echoic memory, as does a doctor listening to a patient’s heart.
In conversation, words and phrases enter a neural circuit in working memory called the phonological loop. Each phrase is held here for up to several seconds and has to be interpreted by the brain before the next one arrives and erases it – which is why listening to a person who speaks very rapidly requires concentrated attention. When we try to hold onto an address or telephone number, it is possible to keep a few words or numbers active in the loop by constantly repeating them. Still, this information is very vulnerable to interference. For example, being told by a receptionist to have a nice day as an addition to some important information can be counterproductive: it can be just enough to make you forget the vital details that you were repeating in your head.
Phonological loop
This brain scan taken while someone was repeating words to keep them in memory shows a loop of high activity in the cortical areas involved in this process.
The echo of times past
Hearing a snippet of sound – a line of a song, the ticking of a grandfather clock, or the sea lapping against the shore – can be enough to transport you back to another time or place.
