Sound localization: Where did that noise come from?

March 12, 2018, Ludwig Maximilian University of Munich
Credit: CC0 Public Domain

The ability to estimate distances to sound sources accurately can be crucial for survival. A new study carried out under the direction of Professor Lutz Wiegrebe at the Department of Biology at Ludwig-Maximilians-Universitaet (LMU) in Munich sheds light on a novel mechanism that is employed by humans to estimate their relative distance from sound sources. The investigation reveals that humans can perform this task more efficiently when they are allowed to move. The findings are published in the Proceedings of the National Academy of Sciences (PNAS).

"We humans find it difficult to assess, either visually or acoustically, how far away an object is from us," Wiegrebe says. "Our visual system makes use, among other things, of the phenomenon of parallax. When we move, the apparent position of an object that is closer to us moves more within our visual field than an object located further away. This relative motion provides information about the relative of the two objects. Localization of sounds is particularly challenging when the nature of the sound source is not clearly defined. It is not that difficult for us to estimate our distance from a speeding ambulance when we hear its siren. But when the sound is unknown, we cannot tell whether we are hearing a faint sound close by or a louder sound further away.

Wiegrebe and his team set out to determine how our hearing system copes with this situation. The experiments were carried out in a non-reverberant chamber to ensure that the participants could not assess relative distances from the locations of sounds on the basis of echoes or reverberation. The experimental subjects wore blindfolding goggles and their head motions were monitored. They were seated facing two sound sources that could be positioned at different distances from the subject. One of the sources, chosen at random, emitted high-pitched and the other low-pitched sounds. The subjects' task was to determine which of the sound sources was closer to them. "Participants who moved their upper bodies sideways - so that the sound sources were further to the right and then further to the left - were better able to estimate the distance between the sound sources. This result demonstrates that humans can use auditory motion parallax to estimate relative distances from sound sources," Wiegrebe says. In fact, subjects were able to do so even when the distance difference between the two sound sources was only 16 cm.

The researchers then carried out two further experiments. In one of these, the subjects were passively moved left-and-right on a motion platform, and in the other the loudspeakers were moved. The results showed that the participants performed best when they were allowed to move actively. "This interaction between self-motion and the auditory system is remarkable," says Wiegrebe. Clearly, it facilitates processing of the expected change in the relative positions of the sound sources in the brain. This mechanism is also an advantage in situations in which different sounds impinge on the ears from different directions. "For example, moving around at a party helps us to discriminate between sounds in the hubbub. Movement alters the spatial sound properties in our ears and thus enables us to determine which sources are closer to us."

As the study shows, humans readily make use of auditory motion parallax associated with self-motion to localize sounds. "However, with practice, it is also possible to improve one's perception of auditory parallax." Whether or not other mammals exploit auditory parallax is not yet known.

Explore further: How the brain represents sound elevation

More information: Nataliya Kraynyukova el al., "Stabilized supralinear network can give rise to bistable, oscillatory, and persistent activity," PNAS (2018).

Related Stories

How the brain represents sound elevation

March 5, 2018
Changing the shape of human participants' ears has provided new insight into how the brain represents the location of a sound source. The research, published in JNeurosci, highlights the link between sensory encoding and ...

Egocentric hearing: Study clarifies how we can tell where a sound is coming from

June 15, 2017
A new UCL and University of Nottingham study has found that most neurons in the brain's auditory cortex detect where a sound is coming from relative to the head, but some are tuned to a sound source's actual position in the ...

Echolocation learning process involves close coordination between sensory and motor cortex

January 26, 2017
Humans can be trained to use echolocation to estimate the sizes of enclosed spaces. LMU researchers now show that the learning process involves close coordination between sensory and motor cortex.

Visual cues amplify sound

February 13, 2018
Looking at someone's lips is good for listening in noisy environments because it helps our brains amplify the sounds we're hearing in time with what we're seeing, finds a new UCL-led study.

Scientists identify brain area that determines distance from which sound originates

June 11, 2012
Researchers at the Martinos Center for Biomedical Imaging at Massachusetts General Hospital have identified a portion of the brain responsible for determining how far away a sound originates, a process that does not rely ...

Can we unconsciously 'hear' distance?

October 28, 2015
Because sound travels much more slowly than light, we can often see distant events before we hear them. That is why we can count the seconds between a lightning flash and its thunder to estimate their distance.

Recommended for you

How do we lose memory? A STEP at a time, researchers say

March 23, 2018
In mice, rats, monkeys, and people, aging can take its toll on cognitive function. A new study by researchers at Yale and Université de Montréal reveal there is a common denominator to the decline in all of these species—an ...

Brain's tiniest blood vessels trigger spinal motor neurons to develop

March 23, 2018
A new study has revealed that the human brain's tiniest blood vessels can activate genes known to trigger spinal motor neurons, prompting the neurons to grow during early development. The findings could provide insights into ...

Being hungry shuts off perception of chronic pain

March 22, 2018
Pain can be valuable. Without it, we might let our hand linger on a hot stove, for example. But longer-lasting pain, such as the inflammatory pain that can arise after injury, can be debilitating and costly, preventing us ...

From signal propagation to consciousness: New findings point to a potential connection

March 22, 2018
Researchers at New York University have discovered a novel mechanism through which information can be effectively transmitted across many areas in the brain—a finding that offers a potentially new way of understanding how ...

Using simplicity for complexity—new research sheds light on the perception of motion

March 22, 2018
A team of biologists has deciphered how neurons used in the perception of motion form in the brain of a fly —a finding that illustrates how complex neuronal circuits are constructed from simple developmental rules.

Focus on early stage of illness may be key to treating ALS, study suggests

March 22, 2018
A new kind of genetically engineered mouse and an innovation in how to monitor those mice during research have shed new light on the early development of an inherited form of amyotrophic lateral sclerosis (ALS).


Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.