Effects of runway shift and stay rules on rats' serial pattern learning in the T-maze.

Rats received three-trial series on a T-maze consisting of extended visually distinct left-black and right-striped side runways. During the first phase of training, when allowed to select baited runways within these series, they predominantly alternated their choices. During the second phase, rats received forced-choice serial pattern training of series consisting of two rewarded (R) trials and one nonrewarded (N) trial in two fixed orders, RRN and RNR. In Experiment 1, the rats in the runway shift rule group always received the second R trial when forced down a runway opposite that on the preceding trial in the series and the N trial when forced down the same runway. The rats in the runway stay rule group always received the second R trial when forced down the same runway and the N trial when forced down the opposite runway. In Experiment 2, each rat was conditionally trained with both runway outcome rules as determined by the central alley lighting and the type of food in the side alleys. The rats took longer to reduce their running speed on the N trial within each sequence under the runway stay rule than under the runway shift rule. They also took longer to acquire serial pattern responding for the RNR than for the RRN series only under the runway stay rule condition. When subsequently reexposed to series of free-choice trials on the final phase, rats maintained spontaneous alternating choice patterns under the runway shift rule conditions but either seldom alternated their choices (Experiment 1) or greatly reduced choice alternations (Experiment 2) under the runway stay rule condition. We discussed these effects in terms of rats' natural foraging strategies and as a factor that interacts with other within- and between-series variables that affect serial pattern behavior.