Extra topics for exam revision

Question 1

What is psychoacoustics?

Answer 1

The branch of science that explores the relationship between physical sound and the way our auditory system perceives it

Question 2

What is the difference between the absolute threshold and the discrimination threshold?

Answer 2

• Absolute threshold is the softest sound that we can hear
• Discrimination threshold is the smallest detectable difference between pitch, loudness, timbre, etc.

Question 3

What three things affect the probability of a person responding on a stimulus detection task?

Answer 3

• Sensitivity: how good are you at detecting the stimulus?
• Noise: random internal or external noise that may confuse / mask the detection process

-Bias: how enthusiastic (or reluctant) you are to respond

Question 4

Why does it become more difficult to detect signals close to threshold?

Answer 4

Noise and Signal + Noise distributions increasingly overlap, causing the signal to become indistinguishable from spontaneous sensory activity.

Question 5

What happens to the criterion when a subject is more eager to respond?

Answer 5

• Criterion moves to the left of the curve
• Hit rate will increase, but false alarm rate will also increase

Question 6

What happens to the criterion when a subject is too careful?

Answer 6

• Criterion will move to the right of the curve
• Hit rate will decrease, but false alarm rate will also decrease

Question 7

What are three procedures used to measure hearing thresholds?

Answer 7

• Forced choice procedures
• Method of constant stimuli
• Adaptive procedures for measuring threshold

Question 8

What features of PTA make it an adaptive procedure?

Answer 8

• Level at which the next stimulus is presented depends on how patient responded to the previous stimulus
• Presented stimuli converge upon the threshold level
• Maximises efficiency as most stimuli are closed to the threshold, not wasted, doesn’t require prior knowledge of where threshold actually is
• Homes in on the threshold regardless of the starting point
• Stimulus adjusted by large steps initially, then smaller steps closer to the threshold

Question 9

What do Equal Loudness Contours represent?

Answer 9

The level of dB SPL needed to make a pure tone equal to dB HL at different frequencies

Question 10

How does the Phon Scale work?

Answer 10

• Matches loudness to a 1kHz pure tone
• e.g. 20 phon = 20dB SPL at 1kHz

Question 11

Why do we need to present tones for at least 2 seconds?

Answer 11

Loudness increases with duration of presentation and plateaus after 2 seconds

Question 12

What is Temporal Integration Theory?

Answer 12

To detect sounds, the amount of energy above a threshold intensity value (IL) is summed over a short time and compared to a fixed criterion of threshold energy

Question 13

What three mechanisms contribute to the aggregate neural firing rate for the neural coding of loudness?

Answer 13

• Individual nerves increase their firing rate at higher intensities
• Different nerves in the same place have different individual thresholds (High SR vs Low SR fibres)
• Spread of excitation: as the intensity increases, the basilar membrane movement widens along the cochlea, causing more distant nerves to be activated. Excitation spreads faster on the high-frequency side due to the asymmetry of the travelling wave

Question 14

How does the central auditory system encode pitch?

Answer 14

• Place code: place of stimulation on the basilar membrane
• Temporal code: the phase locking of action potentials (best below 1kHz)

Question 15

What are three features of auditory filters?

Answer 15

• Intensity dependent and asymmetric
• Have widening bandwidth from apex (low frequencies) to base (high frequencies)
• Bandwidth is called the Critical Bandwidth

Question 16

When is masking noise most effective?

Answer 16

• When the width of the masking noise band is best matched to the bandwidth of the cochlear filter
• White noise not used as its bandwidth is too wide to effectively mask the cochlear filter bandwidth
• If masking noise band is too narrow, it will improve the detectability of the tone

Question 17

What is the significance of auditory filters for pitch perception?

Answer 17

• Sound discrimination based on pitch / frequency (additional cue)
• Frequency selectivity
• Frequency resolution by separating components of a complex sound
• Ability to effectively mask stimuli

Question 18

What is temporal integration?

Answer 18

• The ability to sum auditory information over time to improve detection
• Important for speech perception

Question 19

How can OHC damage in hearing loss impact loudness and pitch perception?

Answer 19

• Loss of OHCs = loss of fine tuning (frequency selectivity and loudness recruitment)
• Pathological cochleae have broadened auditory filters

Question 20

Binaural cues: what is sound localisation?

Answer 20

The ability to judge the direction and distance of a source sound in the horizontal plane

Question 21

Binaural cues: what is binaural summation?

Answer 21

Binaural hearing improves gain by 3-6dB compared to monoaural hearing

Question 22

Binaural cues: what is binaural squelch?

Answer 22

The improved ability to focus on a desired sound in background noise when listening through both ears

Question 23

Binaural cues: what is spatial release from masking?

Answer 23

Ability to understand speech improves when the target signal and interfering noise are spatially separated

Question 24

What is the Coincidence Detection Model in ITD?

Answer 24

Postsynaptic neurons have points along delay lines that are maximally responsive when signals from the left and right ears arrive there at the same time