Fig. 6.

Cross-correlograms of single-unit activity in NIf or L1 and multiunit activity in HVc. In each panel, thethin line indicates the measured cross-correlation, and the thick line indicates the shuffled cross-correlation that results from cross-correlating epochs of activity recorded at different times on each channel (see Materials and Methods). For each unit in each bird, the top panel of each pair of panels shows the cross-correlation in the ongoing activity in the 1 sec epochs preceding stimuli. The bottom panel shows the cross-correlation in the activity recorded during playback of BOS. The peaks in the shuffled cross-correlograms computed for BOS playback epochs indicate constant timing relationships between activity on the two channels across multiple presentations of BOS. Negative values of τ indicate that HVc activity leads either the NIf or L1 activity.