ICA Madrid 9/7/ Simulating distance cues in virtual reverberant environments Norbert Kopčo 1, Scott Santarelli, Virginia Best, and Barbara Shinn-Cunningham Hearing Research Center Boston University and 1 Technical University of Košice Slovakia

ICA Madrid 9/7/ For sources near the listener (e.g., distance < 1m): - Interaural level differences change as a function of distance (Brungart & Rabinowitz, 1999; Shinn-Cunningham et al., 2000). Introduction - ILDs can be used as absolute distance cue ( and they are used as such in real anechoic space; Brungart, 1999). - In reverberant space, D/Rs are large, and received sounds are not strongly influenced by reverberation (Shinn- Cunningham et al., 2006). Main goal: Illustrate that binaural simulation of nearby sources in reverberation effective in providing distance information without distorting other aspects of the stimuli.

ICA Madrid 9/7/ Exp. 1. Compare nearby-source distance perception in real anechoic and reverberant environments. Overview Present results of three experiments that study distance perception for nearby sources in real and simulated environments. Consider cues used by listeners. Suggest implications for auditory displays. Exp. 3. Study frequency-dependence of performance in simulated reverberation. Exp. 2. Measure performance in virtual environment, look at importance of ILD and reverberation cues.

ICA Madrid 9/7/ Goal: Compare nearby-source distance perception in real anechoic and reverberant environments. Hypothesis: Performance will be similar because reverberation energy is low for nearby sources. Exp. 1: Real Environments

ICA Madrid 9/7/ Stimuli: - broadband pink-noise bursts, - presented at various azimuths, 0.12 to 1 m from listener roving the presentation level, - in a small classroom (T 60 ~0.6 sec). Response: - pointing to perceived target location using a wand with electromagn.sensor. Exp. 1: Real Environments - Methods Analysis: - Bin data by target lateral angle. - Compute correlation coefficient r between actual and perceived stimulus distance (on a log scale) in each lateral bin. - Compare to results of a similar experiment performed in anechoic chamber (Brungart, 1999).

ICA Madrid 9/7/ When simulating distance, choose virtual reverberant space (even for nearby sources) because it provides better accuracy. Exp. 1: Real Environments - Results Anechoic (Brungart, 1999): - good for lateral sources, - bad for medial. Reverberant: - similar to anechoic for lateral sources, - very good for medial.

ICA Madrid 9/7/ Goals: Compare real and virtual environments. Analyze contribution of ILD and reverberation cues. Hypothesis: Performance similar (or slightly worse in virtual environment because of limitations of simulation). ILD used equally in anechoic and reverberant environments. Exp. 2: Virtual Environments

ICA Madrid 9/7/ Similar to Exp. 1, except: - virtual environment, - only two directions: medial and lateral, - binaural and (ipsi) monaural presentation modes, - blocks of 45 trials, keeping direction and presentation mode constant, - blocks randomly interleaved, - responding by a mouse click on a computer screen. Exp. 2: Virtual Environments - Methods

ICA Madrid 9/7/ Exp. 2: Virtual Environments - Results Anechoic: - performance below chance. Reverberant: - small drop in correlation re. real environment (Exp. 1) (by.1 to.2 for lat and for med) - independent of mon/binaural presentation mode Exp. 1

ICA Madrid 9/7/ Exp.2: Virtual Environments - Discussion Why ILD not used: - Not clear, but a follow-up confirmed that ILD was perceptible. When simulating distance, choose virtual reverberant space – simulation is more robust. Why anechoic simulation poor: - technical limitations, - varying simulated environment. D/R changes sufficient to explain difference between lat/med.

ICA Madrid 9/7/ Exp. 3: Spectral Content Goals: In anechoic environment, distance perception deteriorates for high-frequency lateral sources (Brungart, 1999). Measure frequency dependence in reverberation. Hypothesis: In reverberation, dependence on spectral content will be different (compared to anechoic environment), because of the dominant reverberation cues. Methods: Similar to Exp. 2, except: Stimuli are 200-Hz wide noise bursts centered at.4, 3, and 5.7 kHz.

ICA Madrid 9/7/ At low frequencies: Both lat and med performance very good (med better than broadband data from Exp. 2). Exp. 3: Spectral content - Results At higher frequencies: - Lateral: drops slightly. - Medial: drops strongly.

ICA Madrid 9/7/ When simulating distance, choose virtual reverberant space – performance is less frequency dependent. Improvement in medial performance over Exp. 2: - possible effect of adaptation to environment (inconsistent in Exp. 2) - similar effects shown in learning studies (School- master et al., 2004) Exp. 3: Spectral content - Discussion Difference in spectral effect re. anechoic: - not consistent with ILD or reverberation-related cue.

ICA Madrid 9/7/ Technology used to simulate auditory distance should use reverberant simulation because it is -more accurate (even in real environment), -less sensitive to simulation quality and stimulus spectrum. Good news: The simulation -does not need to be binaural, -might not need to require nearby sources if reverb-related distortions don’t matter (as ILDs do not contribute), -might require to be consistent. Bad news: Even simulation that includes reverberation does not provide usable cues for frontal high-frequency stimuli  relative cues (e.g., overall level) may be required. Conclusions Research supported by US AFOSR, US National Institutes of Health, US National Academy of Sciences and Slovak Science Grant Agency