Hearing

Question 1

what is a sound

Answer 1

sound arises from the movement or vibration of an object
the movement squeezes air molecules together and pulls them apart and the pressure wave spreads outward towards the listener

Question 2

how is pitch expressed?

Answer 2

in Hertz - the number of times a period is repeated every second so a sound with a period of 5ms has a frequency of 200Hz

Question 3

what are some attributes of sounds

Answer 3

physical - amplitude, frequency, complexity

psychological - loudness, pitch, timbre

Question 4

how is loudness defined

Answer 4

attribute of auditory sensation in terms of which sounds can be ordered on a scale from quiet to loud

Question 5

how are decibels defined

Answer 5

scale for measuring intensity of one sound compared to another

Question 6

how is pitch defined

Answer 6

attribute of auditory sensation in terms of which sounds can be ordered on a musical scale

Question 7

how is timbre defined

Answer 7

attribute of auditory sensation in terms of which a listener can judge two sounds similarly presented and having the same loudness and pitch are disimilar

Question 8

what is meant by ossicles

Answer 8

found in middle of ear

Question 9

what is meant by stapedial reflex

Answer 9

automatic muscle contraction in middle of ear in response to loud sounds - muscle stiffen in ossicular chain to prevent damages to cochlea (inner ear)

Question 10

whats the cochlea

Answer 10

principal job of cochlea is to act as a frequency analyser to convert energy at different frequencies into neural activity in different fibres of the auditory nerve

Question 11

whats the basilar membrane

Answer 11

vibrates when the stapes move the fluid in the inner ear

Question 12

what’s the intensity (loudness) of a tone coded by?

Answer 12

how quickly the fibres are discharging in the auditory nerve

Question 13

describe the auditory nervous system

Answer 13

1. cochlea acts as a frequency analyser
2. superior olive analyses the location of sound
3. inferior colliculus and medial geniculate analyse pitch
4. primary auditory area in the cerebral cortex analyses higher order features of sounds including their spectral shape

Question 14

what is frequency selectivity

Answer 14

ability to separate out sounds with different frequencies that occur at the same time
- determined by the properties of the basilar membrane

Question 15

how do we know the basilar membrane is so selective?

Answer 15

we demonstrate this using a selective laser interferometry
- this measures the responsiveness of the basilar membrane in terms of speed of its movement and we can see that the basilar membrane is selective because the velocity of the membrane at the tested location depends on the frequency of the tone

Question 16

what does frequency selectivity help with?

Answer 16

good for speech perception
- helps distinguish a vowel from another through distinguishing the formats
- the spectrum of sound starts at the larynx then the vocal chords
- the vowels in speech are characterised by patterns of peaks and valleys in their spectra

Question 17

whats the bottom up effect on hearing

Answer 17

ascending to different connections
- cochlea -> cochlear nucleus -> superior olive -> inferior colliculus -> cortex

CCSIC

Question 18

Describe the ganong effect as a top down effect on hearing

Answer 18

the ganong effect occurs when ambiguous speech is heard - listener categorises the sounds in a way that forms a real word (between g and k)

Question 19

describe phenomene restoration as a top down approach on hearing

Answer 19

trick system into hearing a sound that is not there / long term language can create or retrieve illusions of sounds not present

Question 20

describe the mcgurk effect as a top down effect on hearing

Answer 20

auditory illusion when someone looks like they’re saying BA we hear BA but they might be saying something else / visual information distorts auditory perception

Question 21

Describe the sinewave speech as a top down effect on hearing

Answer 21

speech signal in which the formats of speech have been replaced with pure tones tracking the intensity modulations of those formats over time

Question 22

why do we need to locate the sources of sounds

Answer 22

• location is important for information itself
• location of sound may orient visual attention
• sound location can separate sequences of sounds arising from different locations

Question 23

Describe azimuth and elevation

Answer 23

• azimuth: left to right, 0 azimuth is straight ahead
• elevation: positive above 0 and negative below 0 up and down

Question 24

Describe the minimum audible angle (MAA)

Answer 24

all suspended cylinders are speakers
minimum angle that allows you to carry out experiments to see how far we can hear sound
- when MAA is at 0-1 degree angle, ppts can tell where sounds are at low frequency
- as angle increased, the frequency increases and decreases with peak at 14 degree angle

Question 25

how do we know where sound is coming from

Answer 25

when the source of sound is on the left - Inter aural timing difference (ITD)

when the source of sound is on the left the head shields the right ear from the sound (head shadow) and it generates an inter aural level difference (ILD)

Question 26

how does ITD vary with azimuth

Answer 26

when a sound comes from one side of an adult head (azimuth 90 degrees) the ITD is 0.65 miliseconds (650us)

Question 27

how does ILD vary with azimuth

Answer 27

when a sound comes from one side of an adult head (azimuth 90 degrees) the ILD is about 20dV at 6000Hz dimishing to 0dB at 200hz