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

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

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