Binaural Hearing

1
Binaural Hearing

• Or now hear this!
• Upcoming Talk Isabelle Peretz
• Musical Non-musical Brains
• Nov. 22 _at_ 12 noon Lunch
• Rm 2068B South Building

2
TLA 6 2 Two Ear Hearing

• Purpose of TEH
• Spatial hearing and understanding
• Activity
• Walk rapidly down a hallway while plugging one
  ear
• Halfway through hallway, switch to plugging the
  other ear
• Switch order of plugging the two ears and repeat
• Write-up
• Does having a plugged ear change how you walk
  down a hall? How did changing the plugged ear
  affect your motion?

3
Hearing Binaurally(Yost chapter 12)

• Binaural two ear hearing
• Combination of information to determine spatial
  position
• Azimuth
• Not distance
• Not vertical position
• Stationary localization
• Different cues available with motion
• Interaural cues for binaural hearing
• Interaural Loudness Difference (ILD)
• Interaural Intensity Difference (IID)
• Interaural Timing Difference (ITD)
• Interaural Phase Difference (IPD)

4
Interaural Timing Differences (ITD)

• Onset of auditory stimulation
• Does not vary across frequency
• Salient with lower frequencies (lt 1500 Hz)
• Maximum delay of lt 1 ms
• Dependent on head-size
• Angle of stimulation
• Critical for short events
• Clicks, bursts
• Less important for enduring events
• Noise, speech

5
Interaural Phase Differences (IPD)

• Relative phase of stimulus across ears
• Critical region is lt 800 Hz
• No IPD at 833, 1666 Hz
• Noticeable differences of phase
• Minimum displacement 0.2 ms
• Enduring sound events
• Noise, speech
• Change in phase triggers change in localization
• Basis of the Precedence Effect

6
Interaural Loudness Differences (ILD)

• Relative intensity across ears
• Critical region
• gt 2 kHz
• Ecological constraints 800 Hz
• Up to 20 dB SPL attenuation (over 8 kHz)
• Sensitive to 1 dB SPL difference
• Total masking 8 10 dB SPL
• Similar to natural head shadow
• Oldest theory of directional hearing (1870s)
• Ambulance direction
• Open window determines positions for high
  frequency siren

7
Duality Theory of Directional Hearing

• Frequency region determines salient cues
• Lower frequencies 40 1500 Hz IPD, ITD
• Higher frequencies 4 20 kHz ILD
• Worst localization performance 1500-4000 Hz
• Harnessing Stationary cues
• Difficult noises
• Diffuse noise, enduring
• Sinewave burst
• Easiest to localize
• Broadband click
• Incorporates multiple cues

8
Minimum Audible Angle (MAA)

• How good is hearing?
• Stationary accuracy separating two sound sources
  (Mills, 1958)
• Play sound, move left/right play again
• Chance performance 50 , threshold 75
• Results
• Azimuth dependence best at center 0,
  logarithmic decline to 75
• Frequency dependent best 40 4000 Hz
• Approx. 3 separation (vision 1)
• Minimum audible movement angle
• Velocity dependent
• Approx. 1 separation

9
Localization with HAs

• Factors affecting localization
• Bilateral vs. Unilateral
• 2 ear vs. 1 ear
• Symmetric hearing loss?
• All sounds located at hearing ear
• If symmetrical bilateral improvement
• Speech in noise release from masking
• BTE vs. ITC/CIC
• BTE microphone outside ear canal
• Directional microphones
• ITE/CIC spectral filtering from pinnae
• Better HA performance with ITC/CIC

10
Localization with Cochlear Implant

• Test unilateral, bilateral cochlear implant users
• ITD, IPD cues
• ILD cues
• HYPOTHESES?
• 3x precision with bilateral implants
• Large individual differences
• Duration using bilateral implants
• Speech ability

11
Head-related Transfer Functions (HRTFs)

• HRTF calculation of the sum of spatial
  parameters
• Distance between the ears
• Pinna filtering
• Spectral shape of resonance harmonics
• Head attenuation
• Nose directionality
• Body absorption
• Hair on the head
• Calculation of HRTF for simulated reality
• Convolve microphone input
• Dummy-head recordings
• Binaural recordings
• Which is best?
• Front-back confusions

12
Binaural Masking

• Vary position of noise energetic masker
• Monaural
• No difference of spatial position and noise
• Similar amount of energetic masking in all
  positions
• Diotic
• No difference of spatial position of noise
• Similar amount of energetic masking
• Dichotic
• Noise to one ear, masker to other
• Release from masking
• Better detection of signal

13
Hearing the Silent World

• Localization
• Study of sound sources
• Sound producing objects relative to listener
• Are sound sources the basis of hearing?
• Visual world
• Light producing objects
• Sun, lamps
• Light reflecting surfaces
• Tables, faces, trees
• Can we detect sound obscuring/reflecting surfaces?

14
Hearing the Silent World

• Sound obstructing surfaces
• Diffuse sound field set behind sound attenuating
  surfaces
• Are listeners sensitive to position of surfaces?
• Test behavioral judgment
• Is the aperture large enough to allow passage?
• Ego-centric judgment facilitates accuracy
• Aperture size affects intensity, spectra
• Randomize intensities, sine wave signals
• Listeners can detect position of sound
  obstructing surfaces

15
Elevation

• Height relative to listener
• How can this be determined?
• Interaural cues?
• Timing difference between the ears
• Mid-Saggital plane
• Loudness difference between the ears
• Absorption by head pinna
• Front-back confusions
• Pinna cues
• Forward, downward facing
• Partially resolve front-back errors

16
Distance

• How far away is a sound source?
• Interaural cues?
• Azimuth does not indicate relative distance
• Pinna cues?
• Slight-downward facing
• More distant cues higher in the perceptual plane

• Salient cues for distance
• Intensity
• Attenuation over distance
• Frequency dependent
• Unreliable indicator
• Reverberation
• Increase in number and lag of echoes
• DEMO

17
Improving Accuracy

• How do listeners judge distance?
• Metrics of perception
• Absolute distance objective scale
• Egocentric distance metric in body relations
• Test
• Judge baby rattle distance egocentric scale
• 1 vs. 2 degrees of freedom
• Arm vs. Arm body lean
• Highly accurate judging 1 or 2 degrees
• Better accuracy than found with absolute distance