Transcript Hearing Science

Auditory Sensitivity,
Masking and Binaural Hearing
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Minimum Audible Pressure (MAP)
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MAP
• Increased intensities needed in low and high
frequencies
• Low Frequencies:
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Middle Ear Impedance characteristics.
• High Frequencies:
• Hair cell populations in high frequencies are
diminished.
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MAP
• Females have about 3 dB better thresholds
than males
• At about age 18 high frequencies begin to
decline due to hair cell atrophy at base of
cochlea.
• At about age 50, a significant decline occurs
at 4000 Hz and above.
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MAP
• Thresholds for discomfort are about 110 dB
SPL across all frequencies.
• Thresholds for pain are about 130 dB SPL.
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Minimum Audible Field (MAF)
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Why the Difference between MAP and MAF
• About a 6 dB difference due to …
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•
•
Calibration differences between transducers
Head/body diffraction effects (low freqs)
Ear canal/concha resonances (high freqs)
• Calibration differences are also responsible
for MAP differences between types of
earphones (e.g., TDH, insert, circumaural).
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Masking
• Generic definition:
•
Interference of one stimulus by another.
• Operational definition:
•
Process by which the threshold of audibility for
one sound is raised by the presence of another
(masking) sound.
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Masking
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Masking
• Generic definition:
•
Interference of one stimulus by another.
• Operational definition:
•
Process by which the threshold of audibility for
one sound is raised by the presence of another
(masking) sound.
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Masking
• Cross Hearing
•
The ability to hear a stimulus in the ear
opposite the test ear, that is, the non-test ear.
• Interaural Attenuation
•
The amount of sound attenuation that occurs as
the signal passes from the test ear to the
contralateral cochlea.
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Example of cross hearing and
interaural attenuation
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Effect of a masking noise.
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Binaural Hearing
• Localization and Lateralization
• Binaural Squelch
• Binaural Summation
• Precedence Effect
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Localization
• Duplex Theory of Localization
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Interaural time differences
Interaural level differences
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Polar plot showing
IATD & IALD
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Neural mechanism used to localize
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Lateralization
• Similar to localization but usually uses
earphones to deliver stimulus.
• Perceptually the sound appears to coming
from inside the head instead of outside the
head (localization).
• Mechanisms
•
•
Interaural level differences
Interaural phase differences
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Binaural Squelch
• Ability to suppress background noise and
attend to a specific auditory signal.
• Also known as auditory figure-ground.
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Binaural Summation
• Improvement in hearing threshold when
compared to monaural hearing.
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•
•
+ 3 dB at threshold
+6 dB at 50 dB
+9 dB at 90 dB
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Precedence Effect
• Ability to localize or identify a signal in a
reverberant (echoic) field.
• Takes first waveform and suppress any
echoes which helps intelligibility.
• Uses first waveform to localize
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Example of Precedence Effect
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Summary
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