1 Auditory Sensitivity, Masking and Binaural Hearing

2 Minimum Audible Pressure (MAP)

3 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.

4 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.

5 MAP Thresholds for discomfort are about 110 dB SPL across all frequencies. Thresholds for pain are about 130 dB SPL.

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7 Minimum Audible Field (MAF)

8 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).

9 dB Hearing Level (dB HL) Based directly on MAP Used in hearing testing Important to take calibration differences into account for different transducers.

10 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.

11 Masking

12 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.

13 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.

14 Example of cross hearing and interaural attenuation

15 Effect of a masking noise.

16 Binaural Hearing Localization and Lateralization Binaural Squelch Binaural Summation Precedence Effect

17 Localization Duplex Theory of Localization Interaural time differences Interaural level differences

18 Polar plot showing IATD & IALD

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20 Neural mechanism used to localize

21 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

22 Binaural Squelch Ability to suppress background noise and attend to a specific auditory signal. Also known as auditory figure-ground.

23 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

24 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

25 Example of Precedence Effect

26 Summary