Abstract
Functional magnetic resonance imaging (fMRI) findings suggest that a part of the planum temporale (PT) is involved in representing spatial properties of acoustic information. Here, we tested whether this representation of space is frequency-dependent or generalizes across spectral content, as required from high order sensory representations. Using sounds with two different spectral content and two spatial locations in individually tailored virtual acoustic environment, we compared three conditions in a sparse-fMRI experiment: Single Location, in which two sounds were both presented from one location; Fixed Mapping, in which there was one-to-one mapping between two sounds and two locations; and Mixed Mapping, in which the two sounds were equally likely to appear at either one of the two locations. We surmised that only neurons tuned to both location and frequency should be differentially adapted by the Mixed and Fixed mappings. Replicating our previous findings, we found adaptation to spatial location in the PT. Importantly, activation was higher for Mixed Mapping than for Fixed Mapping blocks, even though the two sounds and the two locations appeared equally in both conditions. These results show that spatially tuned neurons in the human PT are not invariant to the spectral content of sounds.
Highlights
How space is represented in human auditory cortex is only rudimentarily known
This cluster was used as an unbiased “functional region of interest (ROI)” to test our main question—whether location—sensitive neurons in the auditory cortex are selective to combinations of sound pitch and location—by contrasting the Mixed against the Fixed Mapping condition
Using an Functional magnetic resonance imaging (fMRI) adaptation approach (Grill-Spector et al, 2006; Krekelberg et al, 2006) the current study directly challenged the possibility that this spatial representation is “high level”, in the sense that it represents the spatial location of the sounds independent of their spectral content
Summary
How space is represented in human auditory cortex is only rudimentarily known. Unlike the spatiotopic mapping of visual and tactile pathways, the primary organization of the auditory system is frequency based (tonotopic; Humphries et al, 2010; Striem-Amit et al, 2011). The PT is commonly regarded as a central stage of the dorsal, “where” pathway of the non-primary auditory cortex (Rivier and Clarke, 1997; Romanski et al, 1999; van der Zwaag et al, 2011) but whether it should be considered a “low level” or “high level” in the hierarchy of processing is unclear. We ask whether spatial tuning in the human PT is sensitive or invariant to the spectral content of sounds
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