Loudness & Intensity Discrimination Flashcards
Describe equal loudness contours.
- Measurement of phons (level in dB SPL of an equally loud 1k Hz sine tone)
- Each curve is equal loudness across the frequency range
Describe the effect of BW on loudness/relationship to CBW.
- 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
Describe the effect of BW on excitation patterns.
- 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
What is Weber’s Law?
- 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
What is the “near miss” to Weber’s Law?
- 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)
What mechanisms may contribute to intensity discrimination?
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)
What is loudness fatigue?
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What is loudness adaptation?
- 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
What is a temporary threshold shift (TTS)?
- 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
What does TTS increase with?
- Increasing level (I)*
- Increasing duration (D)*
- Frequency of exposure stimulus (Fe)
- Frequency of test stimulus (Ft)
- Decreasing recovery interval (RI)
What is loudness recruitment?
- 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
What are the 2 explanations for loudness recruitment?
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
How can you calculate equivalent threshold shifts using the equal energy rule?
- 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