Loudness & Intensity Discrimination

Question 1

Describe equal loudness contours.

Answer 1

• Measurement of phons (level in dB SPL of an equally loud 1k Hz sine tone)
• Each curve is equal loudness across the frequency range

Question 2

Describe the effect of BW on loudness/relationship to CBW.

Answer 2

• For energy at moderate levels or greater:
• Sound BW < CBW –> loudness independent of BW
• Sound BW > CBW –> loudness increases

-For low levels, loudness is nearly independent of BW

Question 3

Describe the effect of BW on excitation patterns.

Answer 3

• As BW increases, loudness patterns decrease in height and become broader
• AS BW exceeds CBW, excitation patterns get significantly broader
• Within CBW, excitation patterns will look the same

Question 4

What is Weber’s Law?

Answer 4

• JND (∆S) is a constant proportion (k) of the initial stimulus magnitude (S)
• Weber’s fraction (k) = ∆S/S
• For WBN, relatively flat slope above 20 dB SPL (1 dB slope)
• ∆L=10*log (∆I+I)/I

Question 5

What is the “near miss” to Weber’s Law?

Answer 5

• For tones, there’s a slope to the curves (0.9 dB) due to:
• Nonlinear growth in excitation pattern in response to pure tone stimuli (more recruitment/increased excitation)
• Combination of information from multiple channels across the excitation pattern (improvement –> change in slope)

Question 6

What mechanisms may contribute to intensity discrimination?

Answer 6

1) Role of neural firing rate
- Changes in center of excitation patterns
- Spreading of excitation patterns at low and high frequency edges
- However, not critical for maintaining performance at high levels

2) Role of phase locking
- However, may not be critical because intensity discrimination can occur at high frequencies (>5 kHz)

Question 7

What is loudness fatigue?

Answer 7

-

Question 8

What is loudness adaptation?

Answer 8

• Decrease in firing rate over time in response to a stimulus of constant amplitude
• May also be seen as a decrease in stimulus intensity during the first few minutes of presentation, followed by a period of fairly constant intensity

Question 9

What is a temporary threshold shift (TTS)?

Answer 9

• Threshold increases with noise exposure
• Logarithmically related to duration up to 8-12 hours
• Mostly decreases after time?
• Sometimes called synaptopothy, may just not develop for 10-20 years

Question 10

What does TTS increase with?

Answer 10

• Increasing level (I)*
• Increasing duration (D)*
• Frequency of exposure stimulus (Fe)
• Frequency of test stimulus (Ft)
• Decreasing recovery interval (RI)

Question 11

What is loudness recruitment?

Answer 11

• Change in loudness perception accompanying SNHL, in which low levels are no longer audible but high levels stay the same
• Effect simulated by measuring loudness in masking noise
• Perception of loudness grows quickly
• Why we have compression in HAs: don’t want to amplify everything, just soft/inaudible sounds

Question 12

What are the 2 explanations for loudness recruitment?

Answer 12

1) Compression
- With HL there’s no cochlear amplifier, resulting in linear I/O functions

2) More filters
- No cochlear amplifier results in reduced sharpness of tuning and wider excitation patterns, which go into more auditory filters
- With increased intensity, more neurons are responding

Question 13

How can you calculate equivalent threshold shifts using the equal energy rule?

Answer 13

• Equal energy rule: sounds of same energy create same threshold shift
• OSHA says that exposure to 85 dB for 8 hours is -3 dB increased intensity level = halved time of exposure
• EX: 10 min of exposure to 120 dB is as safe as 20 min of exposure to 117 dB