Figure 3. Prediction of stimulus identity from hilar population responses.

a, Analysis method based on computing Euclidean distance from each response (black diamond) to the four centroids (filled circles) that represent average responses to each type of stimuli. b, Plot of mean accuracy in predicting stimulus identity (A-D) based on the nearest average response centroid, compared with accuracies expected by chance. ** P < 0.0001. c, Plot of the average Euclidean distance between pairs of response centroids evoked by adjacent (115 μm separation) and non-adjacent (230 and 345 μm separation) stimulating electrode contacts. d, Plot of accuracy of predicting stimulus identity based on nearest centroid versus stimulus electrode separation. Pairs of stimuli evoked on adjacent electrode contacts were classified as accurately as stimuli evoked by non-adjacent pairs. Accuracy expected by chance was 50% in this pairwise analysis. e, Distribution of inter-centroid distances between pairs of responses that were correctly (black symbols) and incorrectly (red symbols) classified. Number of errors associated with each inter-centroid distance plotted on X axis. Mean ± SEM of distance for correctly (black circle) and incorrectly (red circle) classified response pairs plotted next to each distribution. f, Cumulative distribution of distances associated with classification errors. Half of the classification errors results from comparisons between response centroids separated by less than 7 Hz (arrow on X axis). g, Plots of accuracy classifying response pairs with occasional errors versus inter-centroid distance. h, Plot of accuracy classifying response pairs with occasional errors versus distance/S.D. ratio. Solid lines represent linear regression fits in both g and h. Black symbols represent the mean Euclidean distance (in g) and distance/S.D. ratio (in h) associated with response pairs that were always classified correctly.