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 Center Department of Cognitive and Neural Systems Boston University * Technická univerzita, Košice, Slovakia and Dartmouth College

2. 2June 6, 2006ASA 06 Providence 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

3. 3June 6, 2006ASA 06 Providence 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.

4. 4June 6, 2006ASA 06 Providence Methods: Stimuli Target (T) – white noise 300-8000 Hz, 200 ms Masker (M) – white noise 200-12000 Hz, 300 ms 30-ms cos 2 ramps T temporally centered in M 40-Hz sinusoidal amplitude modulation, depth of 0.5 Example: modulated T in (nominally) non-modulated M:

5. 5June 6, 2006ASA 06 Providence Methods: Modulation Conditions Modulation type: no modulation T / M modulated in phase only T modulated only M modulated T / M modulated out of phase Envelope:

6. 6June 6, 2006ASA 06 Providence Methods: Spatial Configurations Virtual auditory space, non-individualized anechoic HRTFs, distance 1m Five spatial configurations: Separated Co-located

7. 7June 6, 2006ASA 06 Providence 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

8. 8June 6, 2006ASA 06 Providence 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). -

9. 9June 6, 2006ASA 06 Providence Perceptual Learning in Exp 1 Perceptual learning observed in all conditions, but with varying size. Effect of modulation on SRM is small in first repeat ( ) but large in last ( ) - 1 st vs. 5 th repeat

10. 10June 6, 2006ASA 06 Providence 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

11. 11June 6, 2006ASA 06 Providence 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.

12. 12June 6, 2006ASA 06 Providence 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. -

13. 13June 6, 2006ASA 06 Providence 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. -

14. 14June 6, 2006ASA 06 Providence 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.

15. 15June 6, 2006ASA 06 Providence 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.