Psychoacoustic Tuning Curves

Question 1

What is the difference between a physiologic
tuning curve and a psychophysical tuning curve?

Answer 1

A physiologic tuning curve is measured using electrodes. Because electrodes are used, it is possible to know which part of the basilar membrane is responding. A psychoacoustic tuning curve is measured using masking and behavioral responses. Masking is used to isolate a particular place along the basilar membrane.

Question 2

What is loudness summation and why is it
evidence for auditory filters

Answer 2

Loudness summation is the phenomenon where a two-tone complex with components of equal db SPL is perceived as louder if the two tones are further apart frequency-wise. This also applies with a narrowband noise vs. a broadband noise, where the broadband noise is perceived as louder, even if the two are presented at equal dB SPL. This is evidence for auditory filters because it indicates that the auditory system processes sound differently if the sounds are in multiple filters. If there weren’t overlapping filters, it shouldn’t make a difference if the tones were close together or far apart (in the first example) or if the noise had larger or smaller bandwidth (second example, again, with dB SPL being equal).

Question 3

each place on BM is sensitive to a best frequency, but will it also respond if you present a tone at a lower frequency at a higher level?

Answer 3

YES

Question 4

What does it mean to say that the cochlea is modeled as a bank of overlapping filters?

Answer 4

Each place along the basilar membrane is sensitive to a “best frequency” but will also respond at other frequencies at greater presentation levels

Question 5

How does the auditory filter shape change with
loss of cochlear outer hair cells?

Answer 5

With loss of cochlear outer hair cells, the sharp
tip is lost and the auditory filter as result
becomes broader. The best frequency or
characteristic frequency of the auditory filter
shifts downward.

Question 6

What are 3 perceptual consequences of the
change in auditory filter shape?

Answer 6

Elevated hearing thresholds (hearing loss)
Increased susceptibility to masking
Pitch perception ability decreases

Question 7

Explain loudness summation and how it is related to the critical bandwidth

Answer 7

how perceptual system (as) perceived loudness as you add components to a sound
sounds differently based on two tone complex or wider band signals (images) and if sounds are further apart, covering multiple critical bands (filters) vs when they are closer together, perceives it as louder when it is broader or two tones apart

Question 8

Can tell difference between two different sounds in two different filters

Answer 8

resolved components

Question 9

Can not tell the difference between two different sounds because they are within the same filter

Answer 9

unresolved components

Question 10

Why does a broader auditory filter have
increased susceptibility to masking?

Answer 10

The sharp tip of a sharply-tuned filter can “filter out” masking noise; if the filter becomes less sharply-tuned then the masking noise is in the same filter as the target and therefore the target is more vulnerable to masking. Recall that increasing the bandwidth of the masker only shifts the threshold of the target up to the point where the bandwidth of the masker equals the critical bandwidth of the auditory filter. In other words, noise falling outside of the filter does not affect threshold. If the filter bandwidth is broader, then there is increased susceptibility to masking because there is more noise that falls within the filter than if it were sharply-tuned

Question 11

Explain how cochlear hearing loss affects the shape of the auditory filter. What are the perceptual consequences of this?

Answer 11

loss of nonlinearity
shape: creates broader shape and less sharp tip, shifts best frequency to lower frequency
messes with tonotopic arrangement of cochlear
perceptually: lose fine tuning & HL