Neuronal Representation of Auditory Distance Percepts vs. Cues in Human Auditory Cortex

Perceiving the sound source distance is important in many everyday activities. For sources near the listener, two dominant intensity-independent cues are available, the direct-to-reverberant energy ratio (DRR) and the interaural level difference (ILD). Previous studies identified the planum temporale (PT) and posterior superior temporal gyrus (pSTG) as auditory cortical areas important for distance processing. However, it is not clear whether the identified areas represent integrated percepts of distance, per se, or the discrete cues based on which it is created. To address this, we combined behavioral and neuroimaging experiments with advanced computational modeling.

We conducted human behavioral (15 participants with 5 self-reported females) and fMRI experiments (15 participants with 5 self-reported females) in a virtual reverberant environment using broadband noise stimuli. The availability and congruency of the DRR and ILD cues were manipulated to identify cortical areas encoding distance cues vs. distance percepts.

Behavioral results showed that distance percepts were stronger when both cues were available and congruent, confirming that both cues are used when listeners judge distance. A univariate fMRI analysis identified areas in the PT + pSTG as encoding the DRR cue. An ROI-based multi-voxel pattern analysis (MVPA) over the whole PT + pSTG region found a significant difference between Congruent and Incongruent stimuli, likely representing the distance percept.

The PT + pSTG region encodes both the distance cues and percepts. However, while the cue encoding is local, the percepts are encoded in a distributed network.