Stream segregation with high spatial acuity

Abstract

Spatial hearing is widely regarded as helpful in recognizing a sound amid other competing sounds. It is a matter of debate, however, whether spatial cues contribute to "stream segregation," which refers to the specific task of assigning multiple interleaved sequences of sounds to their respective sources. The present study employed "rhythmic masking release" as a measure of the spatial acuity of stream segregation. Listeners discriminated between rhythms of noise-burst sequences presented from free-field targets in the presence of interleaved maskers that varied in location. For broadband sounds in the horizontal plane, target-masker separations of !8 permitted rhythm discrimination with d 0 ! 1; in some cases, such thresholds approached listeners' minimum audible angles. Thresholds were the same for low-frequency sounds but were substantially wider for high-frequency sounds, suggesting that interaural delays provided higher spatial acuity in this task than did interaural level differences. In the vertical midline, performance varied dramatically as a function of noise-burst duration with median thresholds ranging from >30 for 10-ms bursts to 7.1 for 40-ms bursts. A marked dissociation between minimum audible angles and masking release thresholds across the various pass-band and burst-duration conditions suggests that location discrimination and spatial stream segregation are mediated by distinct auditory mechanisms.

Room and head coloration can induce obligatory stream segregation

“…Nevertheless, the spectral differences tested in the present study were sufficient to produce obligatory streaming. These results are in agreement with those obtained by Middlebrooks and Onsan (2012) who parametrically measured stream segregation in the free field. They showed that voluntary streaming could be obtained in the median plane where head filtering induce subtle spectral changes which depend on position.…”

Six Degrees of Auditory Spatial Separation

“…Similarly, in the anesthetized cat, Middlebrooks and Breman found an order of magnitude improvement in spatial selectivity using two concurrent but interleaved streams of rhythmic stimuli (Middlebrooks and Bremen 2013). Spatial separation of only 8°was required for individual neurons to become entrained to one of the two streams and human subjects performed well on the same task at this separation (Middlebrooks and Onsan 2012). This spatial separation compares well with the maximum performance we observed here at around 6°f or our nonstreaming, concurrent stimulus task.…”

The what, where and how of auditory-object perception

“…When a rhythmic sequence of identical sound bursts is presented from a single location, it is perceived as one source by human observers. However, such a sequence is perceived as two sources, each with a distinct rhythm, when the sound sequences are presented from two spatially separated locations 49 . Neural correlates of this paradigm are observed in the auditory cortex of anaesthetized cats 50 .…”