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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:• 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 …• 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• 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.• + 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