Group Redundancy Measures Reveal Redundancy Reduction in the Auditory Pathway

The way groups of auditory neurons interact to code acoustic information is investigated using an information theoretic approach. Identifying the case of stimulus-conditioned independent neurons, we develop redundancy measures that allow enhanced information estimation for groups of neurons. These measures are then applied to study the collaborative coding efficiency in two processing stations in the auditory pathway: the inferior colliculus (IC) and the primary auditory cortex (A1). Under two different coding paradigms we show differences in both information content and group redundancies between IC and cortical auditory neurons. These results provide for the first time a direct evidence for redundancy reduction along the ascending auditory pathway, as has been hypothesized by Barlow (1959). The redundancy effects under the single-spikes coding paradigm are significant only for groups larger than ten cells, and cannot be revealed with the standard redundancy measures that use only pairs of cells. Our results suggest that redundancy reduction transformations are not limited to low level sensory processing (aimed to reduce redundancy in input statistics) but are applied even at cortical sensory stations.