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

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

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

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


Introduction

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

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Goals

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.

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Methods stimuli

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:

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Methods modulation conditions

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

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Methods spatial configurations

Methods: Spatial Configurations

  • Virtual auditory space, non-individualized anechoic HRTFs, distance 1m

  • Five spatial configurations:

  • Separated

  • Co-located

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Exp 1 methods general

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

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Results of experiment 1

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).

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Perceptual learning in exp 1

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 ( )

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Exp 1 summary

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

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Exp 2 intro

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.

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Results exp 1 exp 2 last repeat

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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Results exp 1 exp 2 last repeat1

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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Summary

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.

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Summary1

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.

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