PSYCHOACOUSTICS: Frequency selectivity, masking, and the critical bands

Question 1

what are the 3 types of masking presentation and which are better?

Answer 1

• Simultaneous (masker and signal applied at exactly the same time)
• Forward (masker is applied before the signal, i.e. forward of the signal)
• Backwards (masker is applied after the signal, signal first, followed by masker)
• More masking occurs in forward and backward masking than simultaneous (Yost 2013)

Question 2

how does the cochlea code for different frequencies of sound?

Answer 2

Frequency detection (selectivity) along the basilar membrane is arranged so that high frequencies are coded for by the hair cells at the stiffer oval window end (base) of the cochlea and the lower frequencies (possessing longer wavelengths) travel to the more flexible/”bouncy” apical end (apex) of the cochlea.

Question 3

How does Place theory explain the tonotopic organization of the cochlea?

Answer 3

• the place theory suggests that different locations along the basilar membrane respond preferentially to diff freq of sound.

-each location along the BM has a preferred freq aka ‘characteristic freq’ or ‘best freq’ to which its most sensitive.

-as sound waves travel through the cochlea, they cause maximum displacement of the BM at diff locations depending on their freq.

Question 4

What are the implications of the physical limitations of the basilar membrane in Place theory?

Answer 4

• two tones with very close frequencies can excite the same location on the membrane.
• This means that they would be processed by the same auditory filter.
• As a result, sounds with similar frequencies may not be discriminated as effectively by the auditory system, leading to potential limitations in frequency discrimination.

Question 5

What is the Temporal theory in auditory processing?

Answer 5

The Temporal theory, aka the Temporal Code, suggests that auditory nerve fibers need to fire at particular phases of a sine wave to faithfully represent the wave’s frequency.

Question 6

What is the firing limitation of auditory nerve fibers according to the Temporal theory?

Answer 6

Due to the refractory period of a nerve fiber, which is approximately 1 millisecond, each auditory nerve can only fire up to 1000 times per second. This implies that a single auditory nerve fiber cannot effectively encode sine waves above 1 kHz.

Question 7

How does the auditory system overcome the temporal firing limitation?

Answer 7

The volley principle addresses the temporal firing limitation by employing multiple auditory nerve fibers to fire in succession. This allows the auditory system to share the load of encoding high-frequency sounds, ensuring that each cycle of the sound wave has fibers available to fire in sequence.

Question 8

What is frequency selectivity in auditory processing?

Answer 8

Frequency selectivity refers to the ability of the auditory system to separate one frequency from another.

Question 9

How does the auditory system achieve frequency selectivity?

Answer 9

To separate two frequencies, they must each fall into different auditory filters.

If they both fall into the same filter, they are no longer perceived as separate tones but instead merge into a single sound.

This can result in phenomena like beating, buzzing, or roughness of sound, depending on how close the frequencies are.

Question 10

How do scientists measure frequency selectivity?

Answer 10

Scientists use masking experiments to determine the limitation on how close two tones must be in order to be perceived as separate. The limitation obtained from these experiments is considered a measure of frequency selectivity or spectral resolution.

Question 11

how do we measure the auditory filter?

Answer 11

by quantifying

• What frequency is it most sensitive to? -> Best frequency
• What other frequencies can it respond to? Under what circumstances? -> Bandwidth and slope

Question 12

Can you explain the process for measuring tone detection thresholds in the presence of masker noise?

Answer 12

1) Present a target tone at the interested frequency

2) Present a masker narrow-band noise centered on the target tone frequency

3) Expand the bandwidth of the masker noise

4) Measure the tone detection threshold in the masker noise

Question 13

what were the findings of the critical band experiment?

Answer 13

At the beginning, the broader the masker bandwidth, the worse the tone-in-noise detection threshold, but!!!

After certain bandwidth, the further increase of the noise bandwidth does not continue to increase the threshold.

Hence, the idea of critical band is born.

Question 14

What is a tuning curve?

Answer 14

A tuning curve is a graphical representation of the response of a sensory receptor or neuron to different frequencies of stimuli. In the context of auditory processing, a tuning curve shows how sensitive a specific location on the basilar membrane (BM) of the cochlea is to different frequencies of sound.

Question 15

How do tuning curves relate to the structure of the cochlea?

Answer 15

Each location on the basilar membrane has its own tuning curve, meaning it responds most strongly to a specific frequency (known as the best frequency) and less strongly to frequencies farther away from that point.

Outer hair cells (OHCs), inner hair cells (IHCs), and auditory nerve fibers (ANFs) are attached to different locations on the basilar membrane.

As a result, they inherit the tuning characteristics of the specific point on the basilar membrane to which they are attached.

Question 16

Why do OHCs, IHCs, and ANFs exhibit similar tuning curves?

Answer 16

Because OHCs, IHCs, and ANFs are associated with specific locations on the basilar membrane, they inherit the best frequencies, bandwidths, and tuning curves of those locations. This is why we observe very similar tuning curves across them.

Question 17

How do we measure neural tuning curves of auditory nerve fibers?

Answer 17

1) Set target tone at low sound level

2) Sweeping tone from low to high frequencies

3) Mark at which frequency the nerve fires above its spontaneous rate.

4) Set the level of target tone a little higher (e.g. 2 dB higher)

5) Repeat step 2 – 4.

6) The nerve responds to the tones that fall within the boundary of the tuning curve

Question 18

What are Psychophysical tuning curves, and how do they differ from neural tuning curves?

Answer 18

Psychophysical tuning curves (PTCs) are similar to neural tuning curves but not identical. While neural tuning curves measure the sensitivity of auditory nerve fibers to different frequencies, PTCs measure the ability of human listeners to detect a target tone in the presence of a masker noise.

Question 19

How is a Psychophysical tuning curve measured?

Answer 19

• Present a target tone fixed at a frequency of interest and presented at 10 dB above absolute threshold.
• Present a masker tone or narrowband noise (with a 50-Hz bandwidth) at a low level, and change the center frequency of the noise from low to high frequency.
• Mark the frequency and level of the masker where the target tone is just detected (at detection threshold), then increase the level by 5 dB.
• Repeat steps 2 to 4.

Question 20

What’s notable about the x-axis label in Psychophysical tuning curves?

Answer 20

In Psychophysical tuning curves, the x-axis label is not stimulus frequency but masker frequency. This indicates that the frequencies of the masker noise are varied while keeping the frequency of the target tone constant.

Question 21

What is Q10 and how is it defined in the context of tuning curves?

How is Q10 calculated?

Answer 21

Q10 is a term used to quantify the frequency selectivity of a tuning curve.

It’s calculated by dividing the frequency of the target tone by the bandwidth at 10 decibels (dB) above the tip of the tuning curve.

Question 22

What does “Frequency of the Target Tone” refer to in tuning curves?

Answer 22

the specific frequency of sound being tested or studied in the tuning curve experiment.

It’s the frequency of the tone that’s presented to the auditory system for assessment.

Question 23

What is meant by “Bandwidth at 10 dB above the Tip of the Curve”?

Answer 23

tip of the curve= point of max sensitivity
- so by +10dB we’re focusing on a region slightly above the threshold where the auditory system begins to respond

Question 24

How is Q10 calculated?

Answer 24

To calculate Q10, you divide the frequency of the target tone by the bandwidth at 10 dB above the tip of the tuning curve.

Question 25

How do we interpret the Q10 value?

Answer 25

This ratio provides a numerical value that reflects the frequency selectivity of the auditory system.

A larger Q10 value suggests better frequency selectivity, indicating the system can more precisely discriminate between different frequencies.

Conversely, a smaller Q10 value suggests lower frequency selectivity, meaning the system is less able to distinguish between nearby frequencies with precision.

Question 26

whats the difference between a narrower and wider bandwidth?

Answer 26

• A narrower bandwidth suggests that the auditory system is highly selective and responds to a limited range of frequencies. This indicates precise frequency discrimination.
• A wider bandwidth indicates lower selectivity, with the auditory system responding to a broader range of frequencies. This suggests less precise frequency discrimination.

Question 27

how do we estimate auditory filters using iso- response curve?

Answer 27

• Experimental Paradigm: Fixed-frequency target tone presented at varying masker levels.
• Objective: Determine the level of masker noise required to mask the target tone just at the threshold of detection.
• Measurement: Participants indicate when they can barely detect the target tone in the presence of varying masker levels.
• Graph: Y-axis represents masker level at signal detection threshold, X-axis represents signal frequency.
• Insight: Provides information about masking properties of the auditory system across different frequencies.

Question 28

what is the Impact of hearing impairment on psychophysical tuning curve

Answer 28

for impaired ears= more flattened, and higher threshold

For normal ears= Sharper, and lower threshold.

Question 29

how do we estimate auditory filters using iso- stimulus curve?

Answer 29

• Experimental Paradigm: Fixed-level masker noise presented at varying signal frequencies.
• Objective: Determine the minimum level of the target tone needed to be detected in the presence of the fixed-level masker noise.
• Measurement: Participants indicate when they can barely detect the target tone in the presence of varying signal frequencies.
• Graph: Y-axis represents signal detection threshold for a fixed masked level, X-axis represents signal frequency.
• Insight: Offers insights into frequency selectivity and shape of auditory filters.

Question 30

What is the Notched noise paradigm?

Answer 30

The Notched noise paradigm utilizes the iso-stimulus paradigm, where the intensity of the background noise (masker level) is fixed while the intensity of the target signal varies. Researchers manipulate the frequency and level of the target signal within a given spectral notch width.

Question 31

What are the findings of the Notched noise paradigm?

Answer 31

• Using thresholds at various tone frequencies and frequency distances from the noise bands, researchers estimate the shape of the auditory filter.
• This filter functions similarly to a bandpass filter, indicating the extent of amplitude attenuation for signals passing through it at each frequency.
• While the representation may appear symmetrical, real auditory filter shapes typically exhibit a steeper slope on the high-frequency side and a shallower slope on the low-frequency side for accuracy.

Question 32

what does a sharper PTC curve indicate?

Answer 32

sharper PTC curve indicates a better frequency selectivity in the auditory system

Question 33

What experimental paradigms have researchers used to study auditory masking?

Answer 33

forward masking and simultaneous masking paradigms.

Question 34

How does forward masking affect Psychophysical Tuning Curves (PTCs)?

Answer 34

Forward masking typically sharpens PTCs. indicates a better frequency selectivity in the auditory system

Question 34

What types of maskers have researchers compared, and how do they affect tuning curves?

Answer 34

Researchers have compared various maskers, including tone, narrowband noise, and spectrally notched noise. Tuning curves generated by tonal maskers appear narrower compared to those by noise maskers.

Question 35

Why are tonal maskers often avoided in auditory research?

Answer 35

Tonal maskers are often avoided due to their potential to create a beating effect, resulting in fluctuations in amplitude when the target and masker tones are similar in frequency. Additionally, tonal maskers can cause the perception of harmonics, combination tones, or difference tones.

Question 36

Why is narrowband noise considered suboptimal for iso-stimulus paradigms?

Answer 36

Narrowband noise is considered suboptimal for iso-stimulus paradigms due to off-frequency listening, which can cause the auditory filter to appear narrower than expected, leading to spectral resolution appearing better than it actually is.

Question 37

What paradigm has been adopted to improve the estimation of auditory filter shape?

Answer 37

Researchers have shifted towards using spectrally notched noise to estimate auditory filter shape, as it avoids off-frequency listening and provides a more accurate representation of auditory filter characteristics.

Question 38

what is off listening?

Answer 38

Off-frequency listening is the use of information in different frequency regions (i.e. from a neighboring auditory filter) to improve performance in masking tasks.

Question 39

why was the use of single side noise to mask the target tone stopped?

Answer 39

Before notched noise was introduced, people used single side noise to mask the target tone, but failed to account for an issue called ‘off-frequency listening’.

Question 40

why is the overlapping of auditory filters along the BM important?

Answer 40

because that means that a person can use either on-frequency or off-frequency listening depending on what they are trying to listen to (or avoid listening to).

Question 41

what is on frequency listening?

Answer 41

On-frequency – the auditory filter which is centred around the target signal (centre frequency) is used

Question 42

what is off frequency listening?

Answer 42

Off-frequency - an alternative auditory filter is used to help reduce the effects of noise and improve the signal to noise ratio e.g. using a filter that is just below the centre frequency of a signal may help to improve signal detection in a noisy environment

Question 43

What is the upward spread of masking in auditory perception?

Answer 43

where lower frequencies can mask a wider range of frequencies than higher frequencies

-It suggests that low-frequency tones can mask higher frequency signals, but the reverse is less likely to occur.

Question 44

How does upward spread of masking affect our perception of speech sounds in noise?

Answer 44

It explains why general background noise interferes more with the detection of high-frequency consonant speech sounds.

Question 45

what are auditory filters?

Answer 45

structures in the auditory system that respond to specific freq

Question 46

how can the bandwidth of auditory filters be measured?

Answer 46

The bandwidth of auditory filters can be measured using methods such as Q3, Q10, Q40, which quantify the bandwidth relative to the filter’s center frequency. + ERB

Question 47

what is the Equivalent Rectangular band (ERB)?

Answer 47

The ERB is a simplified method for quantifying the bandwidth of auditory filters. It assumes a rectangular shape for the filter’s frequency response.

Question 48

How is ERB calculated?

Answer 48

ERB is calculated using the formula ERB(F) = 24.7(4.37f + 1), where F is the center frequency of the auditory filter in kHz.

Question 49

What are the advantages of ERB?

Answer 49

ERB provides a more intuitive and simplified way to quantify frequency selectivity compared to other measures.

Question 50

What are excitation patterns in the auditory system?

Answer 50

-spatial patterns of responses 2 sound
- these patterns refer to the way the BM responds to sound vibrations (displacement patern)

Question 51

How can excitation patterns be visualised?

Answer 51

by plotting the output of each auditory filter involved in response to the masker tone. This allows for a detailed examination of how different frequencies are processed and represented in the auditory system.

Question 52

What insights do excitation patterns provide about auditory processing?

Answer 52

• how the auditory system responds to various sounds and frequencies.
• They help researchers understand the frequency selectivity and response characteristics of the auditory system to different stimuli.

Question 53

What is lateral inhibition and how does it contribute to spectral resolution in the central auditory system?

Answer 53

Lateral inhibition is a mechanism in the central nervous system that enhances spectral resolution by suppressing the activity of neighboring neurons.

This prevents simultaneous excitation of nearby neurons, sharpening the distinction between different frequencies.

Question 54

How does lateral inhibition work?

Answer 54

When a single neuron is stimulated, it responds strongly.

However, lateral inhibition prevents neighboring neurons from becoming equally active, resulting in weaker responses from each neighboring neuron compared to when only one neuron is stimulated

Question 55

Why is it hard to measure lateral inhibition and temporal inhibition psychophysically?

Answer 55

t’s tough to measure lateral inhibition psychophysically because the final behavioral response observed in auditory tasks is influenced by many factors, not just lateral inhibition.

This makes it difficult to isolate and accurately measure the specific effects of lateral inhibition from other auditory processes.

Question 56

How does temporal inhibition work?

Answer 56

When a first-order neuron is excited, it can generate a delayed inhibitory input to decrease the activity of a second-order neuron.

This inhibition affects the later portion of the response from the second-order neuron.

This refinement in the temporal domain helps regulate the neuronal response, enhancing temporal resolution.

Question 57

What did Fletcher’s experiment show?

Answer 57

It demonstrated that when trying to hear a pure tone in the presence of continuous noise, only the parts of the noise near the tone’s frequency affect our ability to hear the tone.

Question 58

How does masker energy affect signal detection according to Fletcher’s experiment?

• the relationship between signal and masker?

Answer 58

The experiment revealed that the ease of hearing the tone depends on how much energy from the noise passes through the filter that’s centered on the tone’s frequency.

Question 59

How does the bandwidth of the auditory filter affect masking effectiveness?

Answer 59

The bandwidth of the filter, which varies with frequency, influences how much masking noise is needed to effectively mask a signal. A broader bandwidth requires more masking noise to fill, while a narrower bandwidth requires less.

Question 59

What determines the effectiveness of masking in auditory perception?

Answer 59

The effectiveness of masking depends on how much of the equivalent rectangular bandwidth (ERB) is filled with masking noise. Ideally, the entire width of the ERB should be filled for optimal masking.

Question 60

why do we use narrowband for masking and not broadband?

Answer 60

• Overhang of masking does not make masking any more effective.
• All that matters is that the ERB is fully filled.

Question 61

How do resolved and unresolved harmonics contribute to the excitation pattern?

Answer 61

Resolved harmonics, which have sufficient spacing to fall into separate auditory filters, produce distinct peaks in the excitation pattern. Each harmonic is processed by a different filter.

In contrast, unresolved harmonics, which are too closely spaced, end up in the same filter, resulting in a single output.

-explains why a larger frequency change is needed to perceive a pitch change at higher frequencies.

Question 61

How does the length of the temporal window affect temporal resolution?

Answer 61

The length of the temporal window determines temporal resolution, with broader windows resulting in poorer resolution.

Question 62

what is amplitude modulation (AM) in the time domain waveform and how does it sound?

Answer 62

• where the amplitude of the wave is varied in proportion to the signal its transmitting while the frequency stays constant

-AM signal will show fluctuations in the height (amplitude) of the waves while the distance between each wave crest (frequency) remains consistent.

-susceptible to noise so AM sounds noisier or grainer compared to FM

Question 63

What is Frequency modulation (FM) in the time domain waveform and how does it sound?

Answer 63

-the frequency of the carrier wave is varied by the amplitude of the audio signal, while the amplitude of the carrier wave stays constant.

• shows consistent amplitude but varying distance between the peaks and troughs of the waves (frequency).
• less susceptible to interference and noise because changes in amplitude do not affect the info carried in the frequency variations so FM quality is clearer