Constructing and disrupting listeners' models of auditory space.
ABSTRACT A major problem for an auditory system exposed to sound in a reverberant environment is to distinguish reflections from true sound sources. Previous research indicates that the process of recognizing reflections is malleable from moment to moment. Three experiments report how ongoing input can prevent or disrupt the fusion of the delayed sound with the direct sound, a necessary component of the precedence effect. The buildup of fusion can be disrupted by presenting stimuli in alternation that simulate different reflecting surfaces. If buildup of fusion is accomplished first and then followed by an aberrant configuration, breakdown of the precedence effect occurs but it depends on the duration of the new sound configuration. The Djelani and Blauert (2001) finding that a brief disruption has no effect on fusion was confirmed; however, it was found that a more lengthy disruption produces breakdown.
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ABSTRACT: This paper reports some of the influences of individual reflections on the timbre of reproduced sound. A single loudspeaker with frequency-independent directivity characteristics, positioned in a listening room of normal size with frequency-independent absorption coefficients of the room surfaces, has been simulated using an electroacoustic setup. The model included the direct sound, 17 individual reflections, and the reverberant field. The threshold of detection and just-noticeable differences for an increase in level were measured for individual reflections using eight subjects for noise and speech. The results have shown that the first-order floor and ceiling reflections are likely to individually contribute to the timbre of reproduced speech. For a noise signal, additional reflections from the left sidewall will contribute individually. The level of the reverberant field has been found to have an effect on the contribution of the individual reflections. An increase in the level of individual reflections are most likely to be audible for the first-order floor and ceiling reflections, and certain reflections from the sidewalls.The Journal of the Acoustical Society of America 04/1995; 97(3):1717-26. · 1.65 Impact Factor
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ABSTRACT: This paper reports on the influence of individual reflections on the auditory spatial aspects of reproduced sound. The sound field produced by a single loudspeaker positioned in a normal listening room has been simulated using an electroacoustical synthesis of the direct sound, 17 individual reflections and the reverberant field. The threshold of detection was measured using the method of adjustment for five reflections using three subjects for noise and speech. The thresholds have been measured for two simulated situations (1) a loudspeaker with a frequency independent directivity characteristics and frequency independent absorption coefficients of the room surfaces and (2) a loudspeaker with directivity similar to a standard two-way system and absorption coefficients according to measurements of real materials. The results have shown that subjects can reliably distinguish between timbre and spatial aspect of the sound field, that the spectral energy above 2 kHz of the individual reflection determines the importance of the reflection for the spatial aspects, and that only the first order floor reflection will contribute to the spatial aspects.The Journal of the Acoustical Society of America 02/1998; 103(1):434-45. · 1.65 Impact Factor
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ABSTRACT: Echo threshold is that critical delay of a logging signal (the echo) at which the echo is "suppressed"--i.e., at which one rather than two events is perceived. It has recently been shown that echo threshold increases in most subjects when they are exposed to a train of redundant information prior to the test stimulus presentation--that is, there is buildup of echo suppression in the presence of the preceding train [Clifton et al., J. Acoust. Soc. Am. 95, 1525-1533 (1994)]. The present investigation measured echo threshold in 25 normal-hearing adult subjects, both for isolated (baseline) test stimuli and for test stimuli preceded by a redundant train of stimuli (buildup conditions). The test stimulus was a 4-microsecond wideband noise burst pair, in which the lead burst was presented from either the left or right side (from near -45 degrees or or near (+)45 degrees in different runs), and the lag burst was presented from the opposite side. Echo delay was varied adaptively, and the subject's task was to indicate on each trial which of two alternative positions (separated by 20 degrees) the lag sources was presented from. Average echo threshold in the baseline condition was 11.2 microseconds (in agreement with previous results) and did not depend on whether the lead burst was on the subject's left or right side. Average echo threshold in the buildup conditions was significantly elevated. Interestingly, there was a significantly greater buildup effect when the lead stimulus came from the subject's right side (average echo threshold: 24.4 microseconds) than when it came from the left side (average: 18.8 microseconds). This result agrees with informal observations made by Clifton and Freyman [Percept. Psychophys. 46, 139-145 (1989)] and suggests that there is more effective suppression of echo information when the lead stimulus originates from the right side (i.e., the side contralateral to the typically dominant hemisphere) that when it originates from the left side. The distribution of the magnitude of buildup effects across subjects (i.e., echo threshold in the presence of the train minus baseline echo threshold) was unimodal and symmetric, both for lag source on left (mean: 14.1 microseconds) and for lag source on right (mean: 6.7 microseconds). These results are discussed in relation to other hearing asymmetries that have been reported.The Journal of the Acoustical Society of America 03/1996; 99(2):1118-23. · 1.65 Impact Factor