If you detect a sound when it starts, does that mean you’ll also notice when it stops? Not necessarily, a recent research study finds. And, as a leader of the investigation pointed out, failing to detect the cessation of a sound can be dangerous
In a study, entitled “Detection of Appearing and Disappearing Objects in Complex Acoustic Scenes” that was published September 27 in the online journal PLOS ONE, five researchers described their findings on listeners’ sensitivity to changes in complex acoustic scenes.
The scientists created artificial “scenes” with multiple pure-tone components, each with a unique frequency and amplitude modulation rate. They asked listeners to detect the onset or disappearance of different sounds within the scenes. The goal of the study, which was conducted at the Ear Institute at University College London, was to understand what makes certain sounds easily detectable while others go unnoticed.
The researchers reported finding “a striking difference between ‘appear’ and ‘disappear’ events.” In other words, the team found that listeners were quick to detect new sounds around them but were much less able to detect when a sound disappears. In busy sound environments, the subjects missed more than half of the changes occurring around them, and the changes that were detected involved much longer reaction times. The effects were observed even in relatively simple soundscapes and didn’t seem to be affected by volume.
IMPLICATIONS OF THE FINDINGS
Maria Chait, PhD, who led the research at the UCL Ear Institute, discussed their significance in an interview with Jen Middleton of the Wellcome Trust, which helped fund the study.
She said, “We might expect to be more sensitive to the appearance of new events. In terms of survival, it is clearly much more important to detect the arrival of a predator than one that has just disappeared.” However, Chait added, “This reasoning doesn’t apply to other situations. Imagine walking in a forest with your friend behind you and suddenly having the sound of their footsteps disappear. Our results demonstrate that there are a large number of potentially urgent events to which we are fundamentally not sensitive. We refer to this phenomenon as ‘disappearance blindness.'”
Not noticing the disappearance of a sound could be dangerous in ordinary contemporary circumstances, such as, for example, failing to observe a sudden silence from a baby’s crib or from a yard where children have been playing.
The study also explored how listeners react in busy soundscapes, where important changes frequently coincide with other events. The researchers observed that even brief interruptions, such as a short beep occurring at the same time as a major change can cause listeners to miss the change.