Cortical substrates of perceptual confusion between pitch and timbre

Pitch and timbre are two fundamental perceptual attributes of sound that help us distinguish voices in speech and appreciate music. Brightness, one of the primary dimensions of timbre, is governed by different acoustic parameters compared to pitch, but the two can be confused perceptually when varied simultaneously. Here we combine human behavior and fMRI to provide evidence of a potential neural substrate to explain this important but poorly understood perceptual confusion. We identify orderly mappings of both pitch and brightness within auditory cortex and reveal two independent lines of evidence for cortical confusion between them. First, the preferred pitch of individual voxels decreases systematically as brightness increases, and vice versa, consistent with predictions based on perceptual confusion. Second, pitch and brightness mapping share a common high-low-high gradient across auditory cortex, implying a shared trajectory of cortical activation for changes in each dimension. The results provide a cortical substrate at both local and global scales for an established auditory perceptual phenomenon that is thought to reflect efficient coding of features ubiquitous in natural sound statistics.