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Sound Localization of Humans

Sound Localization of Humans. By Michael Alexander. Two Approaches to Sound Localization. Passive Sound Localization (human) determining where a sound came from by using acoustic cues imbedded in the sound stimulus Active Sound Localization (dolphin, bat)

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Sound Localization of Humans

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  1. Sound Localization of Humans By Michael Alexander

  2. Two Approaches to Sound Localization • Passive Sound Localization (human) determining where a sound came from by using acoustic cues imbedded in the sound stimulus • Active Sound Localization (dolphin, bat) active emission of a sound signal that echoes off the target, then analyzing returning echoes to determine distance and direction

  3. The Mechanism in Human • 3 separate mechanisms, 2 for horizontal, 1 for vertical • Horizontal • Interaural Time Difference – ITD (for sound <3 KHz) • Interaural Intensity (or Level) Difference – IID or ILD (for sound >3 KHz) • Vertical • Spectral cues

  4. Anatomical Pathway • Signal from Cochlear Nucleus of both ears go to Medial Superior Olive (MSO) and Lateral Superior Olive (LSO) • MSO calculates ITD • LSO calculates IID • Information from both MSO and LSO goes to Inferior Colliculus, which uses these along with spectral cues to compute the direction of sound origin

  5. The Uses of Sound Localization Information From Inferior Colliculus, directional information goes to: • Thalamus then to Cortex for awareness of sound origin • Superior Colliculus reflex movement of head and eye to orient toward sound origin

  6. Interaural Time Difference (<3 KHz) • Based on time delay between sound reaching each ear • Zero delay if come from straight in front or back

  7. ITD Calculation

  8. A Left Ear Leading ITD Scenario

  9. Interaural Intensity Difference (>3 KHz) • Based on the absorption of sound energy by solid medium (head) • Resulting in sound shadow, region of effectively zero energy

  10. The Maps • Each cell in MSO is tuned to particular delay  thus there’s a map of ITD in MSO • This map is relayed to inferior and superior colliculus

  11. The Combination of Maps

  12. The Product • The result is a Computational Map in Inferior Colliculus, where the variables mapped don’t exist in the periphery, instead calculated by neural circuitry

  13. The End

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