Unit 3 (Binaural hearing)

Question 1

HRTF (Head related transfer function)

Answer 1

Documents how sounds are transformed from a point in space to whats actually received at the ears.

Function describing changes in spectrum between source and outer ear is called HRTF.

(encompasses effects of IID, ITD, Pinna response).

Question 2

Stenger Test

Answer 2

Way to test for psychogenic hearing loss. They used to call it malingering.

The test works on the basis of lateralization. if you have an admitted threshold in one ear that is better than the other, you can put in a stimulus that is high enough in level so that you know that the crossover sound exceeds the persons threshold.

Question 3

Duplex Theory

Answer 3

According to the Duplex theory we can localize sounds within those Three Dimensions using time and intensity differences at the two ears. We can determine the angle of a source and detect small changes in that angle.

In psychoacoustics, the use of the two types of cues for the different frequency ranges is known as the duplex theory.

Question 4

Binaural Hearing (advantages)

Answer 4

When we have two ears functioning with more or less equal hearing acuity, we get…

1. a 3D acoustical soundscape (similar to stereoscopic vision)
2. Sound Localization via IID ITD. We can determine the angle of a source and detect small changes in that angle.
3. We can cope with reverberation as long as the first wave front arrives early.
4. In Noisy environments we have improved signal detection in noise and better speech intelligability.

Question 5

BOTH IID and ITD differences

Answer 5

These differences are recognized by specialized neurons in the brainstem (superior olivary complex)

Question 6

Lateralization

Answer 6

When we work with headphones (lateralization takes place inside the head)

if sensation is the same at the two ears, we will perceive the sound as directly between two ears.

If sound arrives earlier in one ear, we tend to hear it in that ear more and lateralize it to that side.

High frequency levels in one ear we will lateralize to the opposite side.

If the sensation level is 10 dB higher in one ear, the sound will be lateralized (heard in that ear alone)

Question 7

Spatial Orientation

Answer 7

We are able to determine direction of souce (localization) and also distance of source (distance estimation).

Question 8

Localization Cues

Answer 8

1. Binaural

(IID) Interaural Intensity Difference: Due to head shadow - a high frequency localization cue.

(ITD) Interaural Time Difference: Time delay between sounds arriving at the left and right ears. No head shadow - a low frequency localization cue.

2. Monaural

Question 9

Distance Estimation

Answer 9

Depends on the level (in open areas) and on reflections in enclosed spaces - combines with experience. Humans are not great at this.

Question 10

SUMMARY

Answer 10

• Using two ears allows us to create a #D acoustical landscape - similar to stereoscopic (two-eyed) vision.
  *According to the duplex theory, we can localize sounds within those 3Ds using time and Intensity differences at the two ears. We can determine the angle of a source and detect small changes in that angle.
  *We can cope with reverberation if the reflected sounds arrive quickly.
  *In noisy environmenys, the use of two ears allows us to hear better, and makes speech more intelligible..
  *TWO EARS ARE BETTER THAN ONE!