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 –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

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

Facial Vision Why don’t blind people bump into things? –Diderot (mid 18 th 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

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

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

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

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

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