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Transcript
Binaural Hearing Or now hear this! Upcoming Talk: Isabelle Peretz Musical & Non-musical Brains Nov. 22 @ 12 noon + Lunch Rm 2068B South Building 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? 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) Interaural Timing Differences (ITD) • Onset of auditory stimulation – Does not vary across frequency • Salient with lower frequencies (< 1500 Hz) – Maximum delay of < 1 ms • Dependent on head-size • Angle of stimulation • Critical for short events – Clicks, bursts • Less important for enduring events – Noise, speech Interaural Phase Differences (IPD) • Relative phase of stimulus across ears – Critical region is < 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 Interaural Loudness Differences (ILD) • Relative intensity across ears – Critical region • > 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 (1870’s) • Ambulance direction – Open window determines positions for high frequency siren 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 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 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 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 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 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 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? 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 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 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 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