[Short intertrial interval as a phrasing cue in the reinforcement-pattern learning in rats]. 
The effect of short intertrial interval as a phrasing cue on the reinforcement-pattern learning was investigated in a rat experiment using a runway.  In the acquisition session, 20 rats were trained for NNR sequence in which two nonreinforced trials were followed by a reinforced one with equal ITI of 30 min.  In the sequence-addition session, a new sequence with consisting of three nonreinforced trials with 30-min ITI was added 30 min and 30 s after the original sequence of trials for Group L-ITI and for Group S-INT, respectively.  Rats of Group S-INT responded on trials 4-6 with the similar pattern of running speed as they showed on Trials 1-3 from the second day.  In Group L-ITI, the running speed on Trial 4 did not decrease.  This suggests that Group S-INT rats learn to use the ITI of 30 s as a phrasing cue not on the first day but from the second day on.  The phrasing effect of short ITI (30 s) was discussed in comparison with that of longer ITI (30 min).