Group Redundancy Measures Reveal Redundancy Reduction in the Auditory Pathway

The way groups of auditory neurons interact to code acoustic information isinvestigated using an information theoretic approach. We develop measures of redundancy among groups of neurons, and apply them to the study of collaborative coding efficiency in two processing stations in the auditory pathway: the inferior colliculus (IC) and the primary auditory cortex (AI). Under two schemes for the coding of the acoustic content, acoustic segments coding and stimulus identity coding, we show differences both in information content and group redundancies between IC and AI neurons. These results provide for the first time a direct evidence for redundancy reduction along the ascending auditory pathway, as has been hypothesized fortheoretical considerations [Barlow 1959,2001]. The redundancy effects under the single-spikes coding scheme are significant onlyfor groups larger than ten cells, and cannot be revealed with the redundancy measures that use only pairs of cells. The results suggest that the auditory system transforms low level representations thatcontain redundancies due to the statistical structure of natural stimuli, into a representation in which cortical neurons extractrare and independent component of complex acoustic signals, that are useful for auditory scene analysis.