PMC

Sharper spatial selectivity during active sound localization is a result of response sharpening. Scatterplots show for each participant the average β value across voxels that exhibited sharper spatial selectivity (i.e., a decrease in ERRF width of 15% or more) during the sound localization condition (y-axis) than sound identification condition (x-axis) at the preferred (filled circles) and non-preferred location (open circles) for the left core region (left) and right CM (right). Circles below the diagonal reference line reflect a decrease in β value in the sound localization condition.

(A) The distortion of interaural time differences (ITDS) in complex (multi-source) listening scenes. Left panel: the spatial lay-out of a complex auditory scene with two sound sources. Middle panel: the sound wave of the listening scene if source 1 is present in isolation (top row), if source 2 is present in isolation (middle row) or if source 1 and 2 are concurrent (bottom row); owing to the sparse character of natural sounds, concurrent sound streams contain time instants in which only one sound source is present (indicated by the gray rectangles). Right panel: a schematic representation of ITDs to be expected if source 1 is present in isolation (top row), if source 2 is present in isolation (middle row), and if source 1 and 2 are concurrent (bottom row). ITDs for concurrent sounds are distorted and fluctuate over time (bottom row) but accurately reflect the position of a single source in time instants when only this sound source is present (gray rectangles). The auditory system is hypothesized to use the ITDs in these time instants for sound localization. (B) Two potential neural codes for spatial separation. The left panel illustrates a neural representation of relative sound location that is independent of the absolute location of the individual sound sources. That is, the pattern of neural activity in the population is determined by the angle of spatial separation between the individual sound sources (α). Importantly, an identical perceptual spatial separation (that is, identical α) will result in the same pattern of neural activity even when the locations of the sound sources differ from those depicted here. By contrast, the right panel shows a neural representation of spatial separation that emerges from the absolute location of individual sound sources. Specifically, the pattern of activity in the neuronal population is determined by the location of the individual sound sources. Thus, an identical angle of spatial separation (α) will result in a different pattern of neural activity when the two sound sources are at locations different from those depicted here.

Horizontal sound localization accuracy with unilateral (gray) and bilateral (black) bone conduction stimulation. A, Symbols denote means, and error bars denote 95% confidence intervals. The gray shaded area reflects random performance. B–E, Symbols denote individual sound localization accuracy data. Symbols above the line of equality reflect subjects with a bilateral sound localization benefit, whereas symbols below the line of equality reflect subjects with a bilateral sound localization disbenefit. CF indicates center frequencies.

Spatial organization by frequency occurring in elements of the auditory system which achieve sound localization from Kandler et al. (2009).