Information Transmission in the Auditory Brainstem Figure 9. Responses to synthetic vowel sounds. Panels A and C exhibit period histograms obtained from ANF responses to the /i/ sound. Responses of two high-sync neurons to the same stimulus are shown in panels B and D. r values indicate strength of phase locking to f0 ( = 100 Hz). Panels E and F contrast SACs computed from high-sync neurons’ (thin lines) and ANFs’ (red thick lines) responses to /i/. Spike trains used to compute SACs in panel D are the ones used in panels A and B. Similarly, SACs in E and F were computed from response whose histograms appear in panels C and D. doi:10.1371/journal.pone.0044286.g009 10L (thick continuous lines). Spectra from other neurons with similar CFs are also included in Figs. 10J–10L (thin dashed lines). All the responses—either in the time or frequency domains— exhibit a tendency of the neurons to follow the frequency of F1. Shapes of the peaks in the histograms of Group 3 neurons’ responses appear broader and more ‘‘sinusoidal’’ than peaks in the response histograms of high-sync neurons. THD values in the responses of high-sync neurons were higher than the distortion carried in the responses of other types of VCN neurons. Likewise, r values computed at the frequency of F1 are also the largest for high-sync neurons. Figure 11 contains the results of the temporal and distortion analyses performed on VCN neurons’ responses to /e/. Thin lines in Figs. 11A, 11C and 11E represent SACs computed from the responses of neurons whose period histograms are in Figs. 10A, 10B and 10C, respectively. Normalized SACs constructed from PLOS ONE | www.plosone.org 13 September 2012 | Volume 7 | Issue 9 | e44286