CS-directed approach to a cue associated with a non-contingent intravenous injection of cocaine in bHR (n=8, black circles) and bLR (n=8, open circles) rats. Data are illustrated as the mean+SEM averaged across 12-trial blocks. ‘Block 0' represents baseline responding during the final habituation session. (a) The probability to approach the area of the cocaine-paired cue during lever-CS presentation. (b) The number of approaches to the lever-CS area during CS presentation (bHR-CS, bLR-CS) or during the ITIs (bHR-ITI, dark gray; bLR-ITI, light gray). (c) The latency to approach the cocaine-paired cue (in seconds, with 8 being maximum). bHR rats developed CS-directed approach (sign-tracking) to the cocaine-paired cue, and bLR rats did not.