Abstract encoding of auditory objects in cortical activity patterns

Abstract

The human brain is thought to process auditory objects along a hierarchical temporal "what" stream that progressively abstracts object information from the low-level structure (e.g., loudness) as processing proceeds along the middle-to-anterior direction. Empirical demonstrations of abstract object encoding, independent of low-level structure, have relied on speech stimuli, and non-speech studies of object-category encoding (e.g., human vocalizations) often lack a systematic assessment of low-level information (e.g., vocalizations are highly harmonic). It is currently unknown whether abstract encoding constitutes a general functional principle that operates for auditory objects other than speech. We combined multivariate analyses of functional imaging data with an accurate analysis of the low-level acoustical information to examine the abstract encoding of non-speech categories. We observed abstract encoding of the living and human-action sound categories in the fine-grained spatial distribution of activity in the middle-to-posterior temporal cortex (e.g., planum temporale). Abstract encoding of auditory objects appears to extend to non-speech biological sounds and to operate in regions other than the anterior temporal lobe. Neural processes for the abstract encoding of auditory objects might have facilitated the emergence of speech categories in our ancestors.

Keywords: categorization; condition-rich design; fMRI; multivariate information-based mapping; temporal cortex.