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Effect of roving Effect of roving on spatial release from masking on spatial release from masking
for amplitude-modulated for amplitude-modulated noise stimulinoise stimuli
Norbert Kopčo*, Jaclyn J. Jacobson, and Barbara Shinn-Cunningham
Hearing Research CenterDepartment of Cognitive and Neural Systems
Boston University
*Technická univerzita, Košice, Slovakia and Dartmouth College
2June 6, 2006 ASA 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
3June 6, 2006 ASA 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.
4June 6, 2006 ASA 06 Providence
Methods: Stimuli
Target (T) – white noise 300-8000 Hz, 200 msMasker (M) – white noise 200-12000 Hz, 300 ms30-ms cos2 rampsT temporally centered in M40-Hz sinusoidal amplitude modulation, depth of 0.5
Example: modulated T in (nominally) non-modulated M:
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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:
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Methods: Spatial ConfigurationsVirtual auditory space, non-individualized anechoic HRTFs,
distance 1m
Five spatial configurations:
SeparatedCo-located
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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
8June 6, 2006 ASA 06 Providence
5
10
15
20
-(thr
esho
ld T
MR
) [dB
]
noIPSmNmSNmOOP
Results of Experiment 1
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Spa
tial R
elea
se fr
om M
aski
ng [d
B]
Compared to no modulation ( ), presence of modulation can decrease ( ), increase ( ), or not change ( ) SRM. Effect is small (up to 2 dB).
-
9June 6, 2006 ASA 06 Providence
5
10
15
20
-(thr
esho
ld T
MR
) [dB
]
noIPSmNmSNmOOP
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 ( )
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Spa
tial R
elea
se fr
om M
aski
ng [d
B]
1st vs. 5th repeat
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Exp 1: SummaryPerceptual 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
11June 6, 2006 ASA 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.
12June 6, 2006 ASA 06 Providence
0
5
10
15
20
-(thr
esho
ld T
MR
) [dB
]
noSNmIPSmNmSNmOOP
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.
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13
15
17
19
21
Spa
tial R
elea
se fr
om M
aski
ng [d
B]
13June 6, 2006 ASA 06 Providence
0
5
10
15
20
-(thr
esho
ld T
MR
) [dB
]
noSNmIPSmNmSNmOOP
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.
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19
21
Spa
tial R
elea
se fr
om M
aski
ng [d
B]
14June 6, 2006 ASA 06 Providence
SummaryFor 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.
15June 6, 2006 ASA 06 Providence
SummaryPerceptual 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.