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
0
20
40
60
80
100
1 1.2 1.4 1.6 1.8 2 2.2
Aperture Height
Per
cen
t Ju
dg
ed P
assa
ble
Short
Tall
Short-LOUD
Tall-LOUD
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
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
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