Effects of interrun interval shift in the reward serial learning of the rat on the straight runway

Using runway training procedure, three experiments examined effects of inte rrun interval (IRI) shift on serial pattern learning in rats. Series consis ted of varying number of 0.045 g food pellets given in a goal box of a runa way. Groups of rats were trained with 24-10 1--0 or 24-16-10-6-3-1-0 series (Experiment 1), 14-7-3-1-0 series (Experiment 2), and 18-12-6-3-1 0 or 18- 7-7-7-1-0 series (Experiment 3), under either short (15-10 s) or long (5-15 min) IRI. In test phases, IRI was shifted from short to long or vice versa . Anticipation of 0 pellet was not disrupted by shortening of IRI, whereas lengthening of IRI eliminated the 0 pellet anticipation of the five- to sev en-item monotonic series but did not eliminate that for the four-item serie s and the nonmonotonic series. These results suggest that rats learn a seri es with different strategies depending on IRI, pattern length, or structura l complexity of a series.