Fig 8. Using neural ensemble correlation statistics to categorize sounds in a three-category identification task.

The sound categories delivered included fire, water, and speech, with six exemplars per category. As shown for a representative IC penetration site, spectral (A) and temporal (C) neural correlations (100 observations × 6 exemplars × 3 categories; see Materials and Methods) show distinct structures across sound categories but are similar within a category. Projections of the neural correlations onto the first two principal components show that spectral (B) and temporal (D) correlation form distinct clusters for each of the three sound categories. (E) Single-response trial classification results for this penetration site. In all cases, classifier performance improves with sound duration approaching near 100% for the full sound duration (1 sec). (F) Average performance across IC penetration sites (N = 11; N = 3 and 8 from two animals). The spectro-temporal classifier has the highest performance, with an average performance of 96% correct classification for 1 s duration. Figure data and related code are available from http://dx.doi.org/10.6080/K03X84V3. IC, inferior colliculus; PC, principal component.