Lecture 9 - Auditory Sensation and Perception 2

Question 1

Why do we need to localise sound?

Answer 1

The location itself may be important
It may orient our attention to other things
Helps with source seperation

Question 2

What is meant by Interaural timing difference?

Answer 2

The interaural time difference (or ITD) when concerning humans or animals, is the difference in arrival time of a sound between two ears.

Question 3

What happens to sound around objects smaller than it’s wavelength?

Answer 3

Sound diffracts (bends)

Question 4

What happens to sound around objects larger than it’s wavelength?

Answer 4

sound is blocked

Question 5

What happens to low frequencies around the head?

Answer 5

Low frequencies diffract around the head - some sound reaches the far ear.

Question 6

What happens to high frequencies around the head?

Answer 6

High frequencies do not diffract:
- creates a head shadow
- limited sound at the far ear

Question 7

What is the smallest interaural level difference humans can detect?

Answer 7

1dB - good sensitivity across frequencies

Question 8

What is meant by Interaural Level
Difference (ILD)?

Answer 8

Interaural level difference refers to the fact that a sound coming from the right side of your body is more intense at your right ear than at your left ear, and vice versa for sounds from the left, because of the attenuation of the sound wave as it passes through your head.

Question 9

When are ILD’s useful?

Answer 9

Only useful at high frequencies

Question 10

What are ILDs and ITDs both used for?

Answer 10

To determine the azimuthal location
High sensitive in both domains

Question 11

How can we use ITDs?

Answer 11

We need to match specific peaks in the soundwave across ears.
ITDs are ambiguous or misleading at higher frequencies

Question 12

How is the pinnae useful?

Answer 12

ILDs and ITDs don’t help with elevation.
The pinnae helps amplify some frequencies and reduce others - create spectral cues by changing the incoming frequency spectrum.

Question 13

To determine elevation and front vs back, what do we rely on?

Answer 13

• The shape of pinnae
• The position of our head

Question 14

What is the Jeffress Neural Coincidence Model?

Answer 14

The Jeffress model (Jeffress, 1948) describes a neural mechanism for the brain to detect very small differences in the time of arrival of sound at one ear compared to the other, and thus determine the horizontal (azimuth) origin of the sound.

Question 15

How is the neural coincidence model meaured?

Answer 15

Using ITD tuning curves - firing rate of a neuron across a range of ITDs.

Question 16

What is opponent process analysis?

Answer 16

• Two sets of broadly-tuned neurons.
• Right hemisphere – tuned to the left half of auditory space (plotted in red).
• Left hemisphere – tuned to the right half of auditory space (plotted in blue).
• The system calculates the difference
  between the two sets to work out where a sound is coming from.

Question 17

How are speech sounds made?

Answer 17

Vibrations from the larynx travel upwards through the vocal tract.
The spectrum of the sound is shaped by the articulators, including:
- soft palate
- hard palate
- tongue
- teeth
- lips

Question 18

what does speech perception rely on?

Answer 18

more than just acoustic signal
top down (cognitive) as well as bottom-up (perceptual) factors

Question 19

What is the McGurk effect?

Answer 19

Perceptual illusion:
visually-presented sounds affect perception of the acoustic signal.
* Use of visual information informs the interpretation of articulatory knowledge.

Question 20

What is our perception of speech sounds affected by?

Answer 20

The meaning of the context - basic intelligibility

Question 21

What does linguistic experience help with?

Answer 21

Help us fill in gaps, correct imperfections and anticipate what’s likely to come next