Academic journal article Perception and Psychophysics

The Relation between Auditory Temporal Interval Processing and Sequential Stream Segregation Examined with Stimulus Laterality Differences

Academic journal article Perception and Psychophysics

The Relation between Auditory Temporal Interval Processing and Sequential Stream Segregation Examined with Stimulus Laterality Differences

Article excerpt

In this study, we examine the effects of laterality differences between noise bursts on two objective measures of temporal interval processing (gap detection and temporal asymmetry detection) and one subjective measure of temporal organization (stream segregation). Noise bursts were lateralized by presentation to different ears or dichotic presentation with oppositely signed interaural level (ILD) or time (ITD) differences. Objective thresholds were strongly affected by ear-of-entry differences, were moderately affected by ILD differences, but were unaffected by ITD differences. Subjectively, A and B streams segregated well on the basis of ear-of-entry or ILD differences but segregated poorly on the basis of ITD differences. These results suggest that perceptual segregation may be driven more effectively by differential activation of the two ears (peripheral channeling) than by differences in perceived laterality.

Our sonic environment consists of events from different sources distributed in space and time. Our perceptual system groups acoustic events that presumably emanate from a single source and segregates those from different sources into separate perceptual streams (see Bregman, 1990). Such processes are likely involved in the cocktail party phenomenon, wherein we selectively attend to a sound source of interest within a multisource environment. In this study, we are interested in how spatial location attributes might be used for segregation. To do so, we exploit an aspect of the perceptual organization of temporally interleaved sounds: that temporal judgments are impaired when they must be made between sounds that are perceived to emanate from different distal sources (Bregman & Campbell, 1971 ; Warren, Obusek, Farmer, & Warren, 1969). Thus, degradation in performance on temporal judgments made between two sounds that vary on some dimension (e.g., location or pitch) might be used as an index by which to determine the relevance of that dimension in stream segregation. Thresholds for the detection or discrimination of auditory temporal gaps (a silent interval between two sounds) may provide a simple measure of auditory temporal acuity for this purpose. In a variant of gap detection, termed between-channel gap detection (see Phillips, Taylor, Hall, Carr, & Mossop, 1997), the effects on gap thresholds of varying the properties of the sounds preceding and following the silent period have been explored. The two properties that have the most striking effect on gap detection are spectral differences between the gap markers (Divenyi & Danner, 1977; Fitzgibbons, PoIlatsek, & Thomas, 1974; Formby & Forrest, 1991 ; Formby, Sherlock, & Li, 1998; Grose, Hall, Buss, & Hatch, 2001; Hall, Grose, & Joy, 1996; Kinney, 1961; Neff, Jesteadt, & Brown, 1982; Penner, 1977; Perrott & Williams, 1971; Phillips & Hall, 2000, 2002; Phillips et al., 1997; Taylor, Hall, Boehnke, & Phillips, 1999; Williams & Elfner, 1976; Williams, Elfner, & Howse, 1978) and ear-of-entry differences (Divenyi & Danner, 1977; Penner, 1977; Phillips et al., 1997; Taylor, Hall, Boehnke, & Phillips, 1999). Spectral and ear-of-entry differences between interleaved sounds are also those that have the strongest influence on auditory sequential stream segregation (Bregman, 1990; Hartmann & Johnson, 1991; van Noorden, 1975).

In the gap detection task, when the stimuli bounding the silent period are presented to different ears, gap thresholds are often 5-10 times higher than those obtained when the same gap markers are presented to a single ear, which can be as low as 2 msec (Formby et al., 1998; Penner, 1977; Phillips et al., 1997). Similarly, gap thresholds were 5-10 times longer when the markers bounding the silent period originated from free-field sources opposite each ear (i.e., at ±90° azimuth) than when both of the markers originated from the same source (Boehnke & Phillips, 1999; Phillips, Hall, Harrington, & Taylor, 1998). …

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