Effect of roving on spatial release from masking for amplitude-modulated noise stimuli

1. Effect of roving on spatial release from masking for amplitude-modulated noise stimuli Norbert Kopčo*, Jaclyn J. Jacobson, and Barbara Shinn-Cunningham Hearing Research CenterDepartment of Cognitive and Neural SystemsBoston University *Technická univerzita, Košice, Slovakia and Dartmouth College

2. Introduction • Spatial Release from Masking (SRM): Detectability of a masked Target sound improves when Target (T) and Masker (M) are spatially separated • Study the interaction between spatial processing (SRM) and temporal modulation processing when detecting masked stimuli ASA 06 Providence

3. Goals • Question 1: How does presence of modulation in T or M influence SRM? • E.g., is SRM larger when T only modulated or when M only modulated? • Question 2: What cues/factors determine performance? • E.g.: space, temporal modulation, grouping. • Performed 2 experiments, differing in Masker level uncertainty. ASA 06 Providence

4. Methods: Stimuli • Target (T) – white noise 300-8000 Hz, 200 ms • Masker (M) – white noise 200-12000 Hz, 300 ms • 30-ms cos2 ramps • T temporally centered in M • 40-Hz sinusoidal amplitude modulation, depth of 0.5 • Example: modulated T in (nominally) non-modulated M: ASA 06 Providence

5. Methods: Modulation Conditions • Envelope: • Modulation type: • no modulation • T / M modulated in phase • only T modulated • only M modulated • T / M modulated out of phase ASA 06 Providence

6. Methods: Spatial Configurations • Virtual auditory space, non-individualized anechoic HRTFs, distance 1m • Five spatial configurations: • Separated • Co-located ASA 06 Providence

7. Exp 1 Methods: general • - 7 normal hearing listeners • - Threshold TMR in 25 different conditions (5 spatial x 5 modulation) • - 5 repeats per subject per condition (+ 1 practice) • - 3I-2AFC procedure, adapting T level; M level fixed • Analysis:- collapse data across co-located and separated configurations- plot across-subject mean threshold TMR and within-subject standard error of mean ASA 06 Providence

8. Results of Experiment 1 • - • Compared to no modulation ( ), presence of modulation can decrease ( ), increase ( ), or not change ( ) SRM. Effect is small (up to 2 dB). ASA 06 Providence

9. Perceptual Learning in Exp 1 1st vs. 5th repeat • - • Perceptual learning observed in all conditions, but with varying size. Effect of modulation on SRM is small in first repeat ( ) but large in last ( ) ASA 06 Providence

10. Exp 1: Summary • Perceptual learning observed over course of experiment, causing growing differences in the effect of modulation on SRM. • At the end, compared to no-modulation:- SRM grows with T modulation (2 dB)- SRM decreases with M modulation or T/M modulation out-of-phase (2 dB)- small effect of co-modulation • Candidate cues:- modulation (detected in periphery or in IC)- space (SOC)- space / modulation as grouping cues- increase in level ASA 06 Providence

11. Exp 2: Intro • Goal: Which cues determine which thresholds • Introduce Masker level uncertainty - Eliminate across-interval overall level change cue:M level roved by ±5 dB between intervals within a 3I-2AFC trial (T level roved as well to keep TMR constant) • Otherwise Exp 2 identical to Exp 1 (7 new subjs). • Results: Observed perceptual learning similar to Exp 1. Next, show only results of last repeat. ASA 06 Providence

12. Results: Exp 1 & Exp 2 – last repeat • - • Left: Rove has huge effect when no modulation or space cue available, small effect when modulation cue only available, no effect when space cue avail. ASA 06 Providence

13. Results: Exp 1 & Exp 2 – last repeat • - • Right: Results w/ no modulation ( ) cue are rove-level dependent. Results w/ modulation ( ) are independent of rove, except for a constant shift. ASA 06 Providence

14. Summary • For broadband noise T masked by broadband noise M: • When T and M are co-located:- T-modulated threshold is worse than M-mod threshold, which is worse than the T/M-mod-out-of-phase threshold- non-mod thresholds are M-level dependent • When T and M are separated:- trends are similar, but differences smaller- non-mod thresholds are worse than mod-thresholds • Perceptual asymmetry: • SRM when detecting absence/reduction in modulation is smaller (by 4 dB) than SRM when detecting presence/increase in modulation. • Possible mechanism: • Non-linear combination of space and modulation cues. ASA 06 Providence

15. Summary • Perceptual learning was observed, and it was stronger for some combinations of spatial/modulation conditions than for others • Different strategies/cues are used for detection of presence vs. absence of modulation. • Effects might be larger after more learning. • Masker level uncertainty - influenced detection when overall stimulus level was the only detection cue, and, to a lesser extent, when modulation cue was available. - did not influence detection when space cue was available. • Very few of these effects can be explained by considering only mechanisms of peripheral/brainstem auditory processing. ASA 06 Providence