1. Consistent and inconsistent interaural cues don't differ for tone detection but do differ for speech recognition
Frederick Gallun
Kasey Jakien
Rachel Ellinger
National Center for Rehabilitative Auditory Research
VA Portland Health Care System, Portland, Oregon

2. All work funded by VA RR&D and NIH-NIDCD
All work funded by VA RR&D and NIH-NIDCD. However, the opinions expressed do not necessarily reflect the position or policy of the Department of Veterans Affairs or the government of the United States

4. The important point for this talk is that the EC mechanism performs identically whether the signal that leads in time is also more intense or not

5. The results for a tone in noise were found to be symmetrical with respect to intensity for a given phase delay, and well fit by the EC model

6. Based on ideas of scene analysis, we postulated that a tone in a multitone masker might not exhibit the same symmetry across level differences observed for a tone in noise
Frequency
Time

7. Based on ideas of scene analysis, we postulated that a tone in a multitone masker might not exhibit the same symmetry across level differences observed for a tone in noise

11. Spatial Release from Masking with Speech Stimuli
Task: Identify speech in the presence of competing speech
Compare performance when target and maskers are colocated with when the target and maskers are spatially separated

12. Listener
Target
Masker

14. 46 listeners varying in age (19-76 years) with normal hearing or mild-moderate hearing loss recruited into three groups: young or old with normal hearing (YNH, n=14; ONH, n=17) or old with impaired hearing (OHI, n=15)
CRM speech on speech masking tested over headphones with no spatial cues (colocated) or with symmetrical maskers separated by 45 degrees
Virtual stimuli processed to preserve:
ITD or ILD only
ITD and ILD (consistent or inconsistent)
Adaptive tracks used to estimate threshold

15. The amount of hearing loss allowed was limited to ensure audibility, as all target sentences were presented at 40 dB above SRT

16. For speech identification in highly similar speech maskers, there is a benefit of consistent cues and ITD alone is better than ILD alone

17. The effects of age and hearing loss are present in overall performance, but relative benefit of the various cues are the same across all three groups.

18. The individual performance with consistent and inconsistent cues is very reliable across all groups.

19. Conclusions
The Equalization and Cancellation model of binaural release from masking predicts symmetrical release patterns for consistent and inconsistent interaural time and level differences
This is found for detection of tones in noise or in multitoned maskers
Speech targets in similar speech maskers do not exhibit this symmetrical release
A useful test of models of binaural release might be the ablility to predict and explain this difference

20. Research support provided by
National Institutes of Health (NIH/NIDCD) R01 DC
and
Dept. of Veterans Affairs
Rehabilitation Research and Development
National Center for Rehabilitative Auditory Research
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