Effects of the stimulus level on the synchronization neurons. Responses of a representative neuron (A, B) and population data (mean ± SD) (C). A-1 to -4: Raster dot of spike occurrence at the best SPL (-1; in pe-SPL), 20 dB below (-2), 40 dB below (-3) and 45 dB below it (-4) (in the same format as Fig. 1A-1). B: The boundaries between the regions found in A-1 to -3 are plotted at each SPL. C: The population data for the same response variables as in B. The values were normalized to those measured at the best SPL (dotted line). *P < 0.05, **P < 0.01 (Fisher's PLSD test following one-way repeated ANOVA).