Listening for change is
something we do for both pleasure and survival. Unless we are in a very
rarefied atmosphere, the soundscape is usually complicated. Even when we are sitting
in the sun out in the country, we have multiple components to the sound scene
we are listening to at any given moment. We hear the rustling of leaves in the
trees and birds singing or quarreling in their branches, but the moving around
of little rodents in the nearby bushes adds to the complexity.
With music on the menu, we
listen to the rise and fall of volume and changes in complexity as instruments
and voices move in and out of the composition of the soundscape. Sometimes it’s
pleasing and sometimes it’s not.
Picking up rapidly on
soundscape changes is a survival instinct that we are still fairly good with.
Not so good as our dog perhaps, or that deer out in the woods.
Sudden changes in volume
are important, of course, but something with large teeth creeping up on you
won’t be adding much to volume. Rather it will be bringing in new sounds as it
tries to approach stealthily. You turn your head, it stops moving and that
sound is gone. You wait a little, shrug and continue and then you hear the
sound appear again. The cat and mouse game continues until – well, that
depends.
In this week’s PLoS ONE,
Constantino et al have their paper in
which they describe a series of experiments to see how easily people can spot
changes to a sound scene as a new sound come is or an old one disappears. The
scenes are non-musical and consist of groups of frequencies played together in
groups of 4, 8 or 14. Experiments were carried out to eliminate problems such as
changes in loudness as one sound appeared or disappeared from the mix.
The results were quite
clear that sounds disappearing weren’t noticed as successfully as sounds
appearing in the mix. The bigger the mix, the less the loss of one component
was noticed, but even in the largest mix, the appearance of an additional sound
was spotted rapidly and successfully.
Clearly our survival mechanism
is dominant and our auditory senses work similarly to our visual ones where we
pick up on a change as a head pops up. Just like the other animals out there,
our first reaction is to get ready to run or take the safety off our gun.
