We know we can't hear everything in a busy area, or even in a quieter space. It's ultimately our attention that guides what sounds reach our conscious awareness. Think of the kids who can’t hear the nagging parent.

But a new study finds another factor that determines if we can hear a sound: Whether that sound is appearing or vanishing.

Scientists asked participants to detect the onset or disappearance of different pure-tone sounds within soundscapes of ranging complexity. They found that listeners are really great at detecting new sounds but far less able to detect when a sound disappears. In fact they missed at least half of the changes when it involved a disappearing sound. This distinction remained within a range of soundscapes, from very simple to pretty complex.

Researchers call this phenomenon "disappearance blindness."  Interestingly, vision studies have found a similar advantage for objects that appear, as opposed to disappearing objects.

This study finds that ultimately the auditory system is not a “change” detector but rather a novelty detector. The researchers note that maybe detecting the appearance of new sounds, like a predator approaching or stranger in the night, is more important for survival than detecting when that sound has gone away.

—Christie Nicholson

[The above text is a transcript of this podcast.]