The role of reverberation in release from masking due to spatial separation of sources for speech identification Gerald Kidd, Jr. et al. Acta Acustica united with Acustica., 2005 Tyler K. Perrachione HST April 2009

Real environments are noisy –Energetic masking: occurs at periphery; target signal is blocked by masker –Informational masking: occurs centrally; target signal competes with masker for auditory attention Real environments exist in space –Spatial release from masking: Detection / comprehension is enhanced if target and masker are spatially distinct –Mechanisms of spatial release: “Better ear” arises from head's acoustic shadow Classic binaural cues (ITD, ILD) allow spatially focused attention Background

Methods Subjects : –5 students, 19-25yrs Stimuli: –Target sentences: CRM sentences “Ready Baron go to red five now.” Modulated narrow frequency bands (8) –Maskers: Different-band (6) speech (DBS) Different-band (6) noise (DBN) Same-band (8) noise (SBN) Fig 1. (Arbogast et al., 2002)

Methods Procedure –Identify color + number pair following target callsign (“Baron”) –Masker at 60 dB SPL –Target varied adaptively by 1-up 1-down rule (50% threshold) 0° azimuth (target) 90° azimuth (masker) 0° azimuth (masker)

Room Characteristics BARE (standard IAC soundbooth) PLEX (surfaces covered in plexiglas, increased reflection of sound) FOAM (surfaces covered in polyurethane, increased absorption of sound)

Results – Masking & Reverberation Intersubject variability in masking, especially in DBS Overall, least masking in DBN SBN shows increased reverberation-related masking from 90° masker only DBS shows increased reverberation-related masking at both 0° and 90°

Results – Spatial Release Greatest spatial release from masking in DBS condition – No effect of reverberation on release Least release in DBN – But NB: least masking in DBN anyway DBN and SBN show trend (n.s.) of reverberation by spatial release interaction – More reverberation results in less spatial release

Summary Increased reverberation results in increased masking; in particular when the signal and masker are spatially separated (DBN, SBN) – Reverberation results in loss of interaural timing and level difference – Loss of both “better ear” and binaural analysis Only in DBS condition does reverberation increase masking of target by colocated (0°) masker – More reverberation -> less separability of the two streams Spatial release from informational masking is unaffected by reverberation – “better ear” or binaural analysis cannot account for spatial release under reverberation – Role of precedence effect, allows informational, but not energetic release