7

Are we able to detect the direction or the distance from which a sound comes with just one ear?

I don't know if the inner ear works as a single point sensor or if it has multiple sensitive regions, like an array of sensors, like the retina.

Or we can only do it if we use both ears? In that case, the source would only be partially located on a 3D space.

Would it be useful to make headphones with multiple speakers for each ear? (Not for different frequencies but at different locations).

0

4 Answers 4

6

The eardrum is a single sensor: The sound pressure which vibrates the eardrum propagates as a single signal in the hammer bone which is attached to the inner surface of the eardrum, i.e. there is no several bones which would detect the pressure on different locations of the tympani (which would probably be inefficient anyway).

Direction-dependent mono-aural cues: Horizontal Spatial hearing cues are mainly driven by differences in time and amplitude of the sound wave in the two ears, while vertical spatial hearing is mostly driven by direction-dependant spectral signature of the head and pinae (HRTF).

--> Studies with single-sided deafness individuals show that it is possible to learn to localize sound sources from HRTF cues in the horizontal planes too.

Agterberg MJ, Hol MK, Van Wanrooij MM, Van Opstal AJ, Snik AF. Single-sided deafness and directional hearing: contribution of spectral cues and high-frequency hearing loss in the hearing ear. Front Neurosci. 2014 Jul 4;8:188. doi: 10.3389/fnins.2014.00188. PMID: 25071433; PMCID: PMC4082092:

To investigate whether single-sided deafness listeners rely on monaural pinna-induced spectral-shape cues of their hearing ear for directional hearing, we investigated localization performance for low-pass filtered (LP, <1.5 kHz), high-pass filtered (HP, >3kHz), and broadband (BB, 0.5–20 kHz) noises in the two-dimensional frontal hemifield. We tested whether localization performance of single-sided deafness listeners further deteriorated when the pinna cavities of their hearing ear were filled with a mold that disrupted their spectral-shape cues. [...] Several listeners with single-sided deafness could localize HP and BB sound sources in the horizontal plane [...]. Localization performance of these listeners strongly reduced after diminishing of their spectral pinna-cues.

This literature review about spatial hearing with impaired ear points some laboratory limitations to the above findings:

it will be necessary to show that it extends to more realistic and challenging listening situations than those typically used in the laboratory, and that the benefits include not only a recovery in sound localization accuracy, but also improved speech-in-noise perception.

The Agterberg et al. 2014 paper also reviews the studies with non-human single-sided deafness and how inborn versus later deafness are involved.

2
  • The, would it be useful to make headphones with multiple speakers for each ear? (Not for different frequencies but at different locations).
    – skan
    Sep 23 at 22:55
  • @skan I don't know, but it would need quite large headphone to have speakers all around the pinna; I found this proceedings paper about it.
    – Noil
    Sep 23 at 23:48
3

The Cochlea that translates sound/vibrations into chemo-electrical (nerve) signals is only a single sensor and therefore directionality cannot be obtained by time-delay estimations.

However, the ear is on one side of the head, and therefore the sound intensity varies when the sound arrives from the side of the ear or from the other side of the head. Therefore, the brain could learn to use this intensity difference to assess the sound direction. Changing the direction of the head while hearing the sound could provide sufficient variations in sound intensity to learn this. The presence of the outer ear channelling the sound would support/amplify such intensity variations.

Using the sound intensity to obtain sound direction allows us to assess if sound is coming from behind.

How good such direction estimate will be depends on the training data set of the human neural network (also known as brain).

3

Yes, to some extent. The shape of human ears filters sound differently depending on direction, see https://en.wikipedia.org/wiki/Head-related_transfer_function

1

The shape of the ear helps with broadband sounds. If you have a cat you can see a similar effect by testing its ability to find the height of a sound source. It can accurately find the source when using a broadband source (hiss), but single freqeuncy (whistle) will confuse it.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.