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Hearing the Silent World

Hearing the Silent World. The Bounce of Sound. TLA: Echolocate in Space. Purpose: Can you echolocate? What properties of objects can you detect? Ingredients Assistant? Hard & Soft object Big and small object Similar size, differently shaped objects Pick two or three tasks

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Hearing the Silent World

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  1. Hearing the Silent World The Bounce of Sound

  2. TLA: Echolocate in Space • Purpose: • Can you echolocate? What properties of objects can you detect? • Ingredients • Assistant? • Hard & Soft object • Big and small object • Similar size, differently shaped objects • Pick two or three tasks • Try to echolocate objects and determine properties • Allow 30 seconds acoustic exploration • Make a guess • Assistant marks right/wrong picks next object • Can you echolocate at better than chance? • How did the properties of objects make them sound different

  3. Finishing up with Acoustic Occlusion • Previous results • Short Ss judge more apertures as ‘passable’ than tall Ss • Louder intensities • Increases likelihood of judged passability • Scaling factor • Sine-wave • No spectral information • No effect on judgments • d’ sensitivity • Highest in louder intensities • How did they do it? • Detect change across aperture expanse • Not the cue to intensity • Change in intensity over space

  4. Facial Vision • Why don’t blind people bump into things? • Diderot (mid 18th century); Hayes (1935) • Facial vision • Pressure to allow surface detection • Supa, Cotzin & Dallenbach (1944) • Sound or Pressure • Both may contribute • Survey of blind individuals (1940’s) • 1/3 Facial vision; 1/3 Sound; 1/3 uncertain

  5. Testing FV vs. Echolocation • Walk to wall in front of you • Stop at closest point of detection • Stop as close as possible • Vary skin covering • Plastic wrap on exposed skin • No effect; subjective reports of ambiguity • Face/no face coverage • Some effect; performance degredation • Sound conditions • Vocal noise • No effect; subjective reports of distraction • Shoes • Some effect; performance degradation • Shoes + Facial cover • Highest echolocation difficulty • What Happened??? • Ear muffs problem

  6. How good is human echolocation? • Dan Kish • Congenitally blind human echolocator • First certified (blind) blindness mobility instructor • Team BATS • Blind mountain biking team (Dan Kish) • Sighted leader + Dan • Hears and navigates around novel areas • Counts landmarks to find route

  7. Limits of Human Echolocation • Texture detection • Clothe, wood, glass, metal • Blind differentiate wood and cloth, metal/glass confusion • Hard vs. Soft • Shape detection • Differentiate circle from square from rectangle etc. • Equal area, differing reflectance properties • Object detection • Close object advantage • Disc detection as small as 5 cm** and string • Use of head-movements

  8. Information for Human Echolocation • Close distances (within 2 m) • Ripple noise pitch: interference between emitted and reflected sound • Total intensity: greatest with close sound board • Far distances (greater than 2 m) • Time delay of reflected sound • Intensity ratio: emitted to reflected • For moving listeners • Doppler shift: used by bats, high speed • Auditory Time-to-contact: dilating reflective surface

  9. Echolocation Research • Can sighted listeners echolocate? • Early experiments - yes with some training • Ask listeners to stop before contact with a wall • After 20 trials avoid contact • Can detect the distance of a wall in front of them up to 7 meters away • Better while moving

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