Figure 4.

A, Examples of a dPEG response to novel stimuli. Raster shows spike times by trials. Two dashed lines indicate the onset and offset of the stimuli. Baseline activity was measured within the 1 s window before stimulus onset. Notice that the baseline is consistent in both PSTHs. Yet, spikes became sparser after 20–30 repetitions. In this example, PSTHs for the first eight trials (blue) in a block of identical stimuli is shows an increased response compared with the PSTH for the last eight trials in this block (red). B, Spike waveform for the neuron in 3A is consistent across the whole recording session for all phases. C, Examples of spike counts by trials for an A1 neuron and a dPEG neuron in response to three novel sounds in three sequential blocks. Red line shows the linear regression fit. Green horizontal lines show the average spike rate in the first and last 16 trials. D, Histograms of changes in response strength in A1 (N = 81) and dPEG (N = 83). Response change is calculated as the difference between the average spike count of the first 16 trials in the block and of the last 16 trials (C, green lines). The vertical dashed lines indicate zero. The green arrows indicated the mean of each distribution. E, Histograms of regression slopes in A1 (N = 81) and dPEG (N = 83). The vertical dashed lines indicate zero. The green arrows indicate the mean in each distribution. F, Box-and-whisker plot of spike counts in dPEG (N = 73) to three novel stimuli sequentially presented in Phase 1. There was no significant difference between blocks, indicating that habituation to the first stimulus did not affect responses to the second and third stimulus. G, Box-and-whisker plot of regression in dPEG (N = 73) slopes of three novel stimuli sequentially presented in Phase 1. The dashed red line indicated 0. Regression slops in all three blocks were significantly lower than zero (p < 0.001 for all). There was no significant difference between blocks, indicating that each novel stimulus was habituated independently.