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Echo suppression and discrimination suppression aspects of the precedence effect
1Vanderbilt University Medical Center, Nashville, Tennessee, USA.
Perception & Psychophysics
|November 14, 1997
Summary
The precedence effect, where a leading sound masks a trailing echo, involves two distinct processes: echo suppression and discrimination suppression. These processes show independent development, especially under conditions of repeated sound exposure.
Area of Science:
- Auditory perception
- Psychoacoustics
- Auditory neuroscience
Background:
- The precedence effect describes how a listener perceives a single auditory event when a direct sound is followed closely by an echo.
- This effect typically leads to echo suppression (inability to hear the echo as separate) and discrimination suppression (inability to discern the echo's location).
Purpose of the Study:
- To investigate whether echo suppression and discrimination suppression are independent phenomena within the precedence effect.
- To examine how these suppression types are affected by stimulus conditions, specifically single versus repeated sound presentations and source spatial separation.
Main Methods:
- Two experiments were conducted using noise bursts presented from two loudspeakers to simulate lead and lag sounds.
- Echo suppression threshold was measured by the minimum delay for detecting two sounds; discrimination suppression threshold was measured by the minimum delay for localizing the echo.
- Experiment 1 manipulated stimulus repetition (single pair vs. train of pairs) to assess 'buildup of suppression'.
- Experiment 2 varied the spatial separation between lead and lag sound sources.
Main Results:
- In Experiment 1, both suppression thresholds were similar for single sound pairs (approx. 5.4 msec).
- However, after repeated sound presentations (buildup condition), echo suppression threshold significantly increased (26.4 msec) compared to discrimination suppression threshold (10.4 msec), indicating distinct development.
- Experiment 2 found no consistent effect of spatial separation on either suppression threshold.
Conclusions:
- The differential buildup of echo suppression and discrimination suppression suggests they are at least partially independent processes.
- These findings imply different underlying neural mechanisms may govern the perception of echo presence versus echo location.
- Further research under buildup conditions is needed to fully understand the role of spatial cues.