Fig 2. Representative 30-min segments of cumulative records of Rats O-1, O-2, O-3, and O-4 from a terminal criterion baseline training session on the three-ply multiple VI VI EXT schedule.

For Rat O-1 the record contains data collected 3 days prior to testing (session 220) For Rat O-2 the record contains data collected on session 136, 2 days prior to testing. For Rats O-3 and O-4, the record contains data collected on the last day of terminal baseline training (session 232 and 194, respectively). Tone (T) or odor (O) components are indicated by corresponding letters above the record. When the pen is depressed neither stimulus was present, and responding was on extinction. The slash marks by the response pen denote the delivery of a reinforcer.