Discriminative odor cues in the runway; further validation and a method for control

Twenty-four albino rats were tested in a 5' straight alley on a double alternation pattern of reward and non- reward--a pattern which previous work has shown to be impossible for the rat to perform on the basis of internal cues or memory. During acquisition, the Ss were rotated through their eight daily trials with the order of running reversed each day. The pattern of reward and non-reward was that of RRNNRRNN, where R and N designate rewarded and non-rewarded trials, with all Ss receiving the same goal event on any given trial. By using an exhaust fan which was mounted beneath the goal box, a continuous stream of air could be drawn through the entire length of the alley to evacuate any odors which might serve as discriminative cues regarding the presence or absence of reward in the goal box. Two groups, 'fan' and 'odor', were designated on the basis of the availability of odors as defined by whether the exhaust fan was operated for that group. A total of sixteen days of acquisition were given, consisting of eight trials per day. The 'odor' group exhibited appropriate patterning (fast on rewarded trials, slow on nonrewarded trials), whereas the 'fan' group showed no such patterning during the sixteen day acquisition period. Two days of transfer training were given. During transfer, the 'odor' and 'fan' groups were subdivided into four groups with acquisition and transfer conditions as follows: 0-0, 0-F, F-0, and F-F. Since the operation of the fan was the only change which occurred in the method during transfer, the stimulus properties of the fan as they affected the subject's behavior could be investigated. Three days of extinction were given. Days 1 and 2 of extinction were given with the fan operating for all Ss. On day 3, the 'odor condition' was introduced for all Ss. Evidence obtained by a comparison of the data from the conditions of acquisition, transfer, and extinction indicates that, although the initial response to odor is an unconditioned one, if a particular goal event is consistently paired with the presence or absence of odor, the presence or absence of that odor will begin to function as a conditioned SD for subsequent Ss. In addition, it was shown that the presence of such odor results in lessened resistance to extinction and a general decrement in running speeds on both rewarded and nonrewarded trials for the 'odor' Ss as compared to those Ss for which the use of the exhaust fan precluded odor- mediated discriminations. Finally, it was determined that the use of an exhaust fan is acceptable as a convenient and effective means of control for this possible source of contamination.