Pausing time as a function of lap and drug condition. (Before contingency switch: Note the initial high ratio decreasing over lap for the wash, DCS, and saline conditions. But the smaller ratio in the CPP condition. After contingency switch: Note the re-initiation of VTE behaviors after the contingency switch, decreasing over lap for the wash, DCS, and saline conditions. Note the clear lack of VTE effects in the CPP condition after the switch in reward contingency. The black line repeated on each condition is the mean VTE for the corresponding wash condition for comparison.