Auditory Localization in Rooms: Acoustic Analysis and Behavior Norbert Kopčo1 Barbara Shinn-Cunningham1,2 Boston University Hearing Research Center 1Cognitive and Neural Systems, Boston University 2Biomedical Engineering, Boston University

Localization in a room: Degraded directional hearing Improved distance perception Goal: Analyze how localization cues are influenced by listener position in a room source azimuth and distance around listener Compare predictions to behavior Outline: Effect of Room on Spatial Cues: Spectral Cues, Interaural Level Differences, Interaural Time Differences Human Localization Performance Conclusions and Future work

Methods Measure KEMAR HRTFs 4 room positions, azimuths 0 – 90° (15° steps), dist 15, 40, 100 cm Analyze effect of reverberation on ILD, ITD, spectrum In terms of mean value and variability Human performance mean and std dev in perceived azimuth within 0-90°, 0.15-1m Positions of KEMAR and listeners Positions of sound source Room 5x9 meters, T60 ~700 ms center wall corner back

Reverberation Alters Spectral Cues HRTF analysis Reverberation Alters Spectral Cues Anechoic Reverberant Left Ear Normalized Amplitude Frequency Spectrum (dB) Anechoic Reverberant Right Ear 50 100 150 200 0.1 0.5 1 5 10 Time (ms) Frequency (kHz)

Magnitude Spectrum (dB) Reverberation Effects Depend on Source Direction, Increase with Distance 0˚ azimuth 90˚ azimuth Left Right Left Right 15 cm Anechoic Anechoic Reverberant Reverberant Magnitude Spectrum (dB) 200 cm 0.1 1 10 0.1 1 10 0.1 1 10 0.1 1 10 Frequency (kHz)

ILDs and Reverberation Source Distance Anechoic ILDs smaller: - with distance and with asymmetric reflections ILD variability: - 0 in anechoic - increase with distance - largest in Center

ITDs and Reverberation Source Distance Anechoic 0.15 m 0.40 m 1 m 1.0 0.8 0.6 X-Corr Peak Coeff 0.4 ITD of x-corr peak independent of position or distance Magnitude of x-corr peak decreases with distance and with number of nearby walls Secondary x-corr peak can be larger than primary 0.2 0.0 0.8 0.6 ITD (ms) 0.4 0.2 0.0 30 60 90 30 60 90 30 60 90 Source Azimuth (degs)

Reverberation and ITD Variation Anechoic baseline Variation is random around mean in Center (and Back ) In Corner (and Ear) the early asymmetric reflections are have more pronounced effect 0.8 0.6 ITD (ms) 0.4 0.2 0.0 -0.2 -0.4 -0.6 -0.8 200 600 1000 1400 1800 200 600 1000 1400 1800 Frequency (Hz)

Human performance Two significant trends: 1) In Back and Corner, bias towards median plane (3.5°) - no correlation with acoustics where Corner and Ear similar 2) Variance in azimuth increases from Center to Corner - consistent with variability in ITD and ILD - however, not consistent as a function of distance

Conclusions and discussion All localization cues affected strongly by reverberation in a room position dependent way Localization performance affected modestly Possible explanations: humans are sensitive to changes in cues over time (precedence effect) listeners are able to estimate effect of reverberation and compensate for it Future work: apply models of auditory processing (Colburn, 1977) to predict how cues are extracted from reverberant signals in the brain look at effects of learning (Kopčo et al., 2001) on localization in rooms