Hurdle-jump responding in the rat as a function of amount and kind of conspecific odor

Abstract

The primary purposes of the present experiment were: (1) to determine whether the hurdle-jump reaction provided a sensitive index of aversion to conspecific odor of nonreward; (2) to gather data on the variables that affect both scent excretion and the reaction to the odor by other rats; (3) to provide a further test for the existence of an odor of reward and a neutral odor. The latter condition involved subjects never receiving reward in the alley. The 230 subjects were of two types. Odorant subjects (Gp. O) received either 112 runway acquisition trials on a continuous reward schedule and 32 extinction trials (Gp. O-C), or 112 acquisition trials on a 50% schedule of reward and nonreward and 32 extinction trials (Groups O-P(T) and O-P), or received 144 trials with no reward in the alley (Gp. O-nt). Escape subjects (Gp. E) jumped a hurdle to escape from odors associated with the above treatments. Several types of escape subjects were employed during odorant acquisition. Groups E-NP(T), E-RP, E-RC, E-nt, and E-cl escaped from odor excreted on nonrewarded trials by Gp. O-P(T), odor excreted on rewarded trials by O-P(T), odor excreted by O-C, odor excreted by O-nt, and from a clean box (Gp. E-cl), respectively. Three additional escape groups were employed during acquisition to test the notion that subjects adapt to the odor of nonreward. Subjects escaped from either odor excreted on early acquisition trials (E-NP(E)), the middle trials (E-NP(M)), or at the end of acquisition (E-NP(L)). Groups E-NP(T) and E-cl continued escaping during odorant extinction. In addition, Groups E-NP(X), E-NC(X), and E-nt(X) escaped from odor excreted by Groups O-P, O-C, and O-nt, respectively., The principal "odor of nonreward" findings were that: (1) transient aversion, possibly due to fear of the apparatus, was seen on early acquisition trials for Groups E-NP(T), E-NP(L), and E-nt; (2) significant aversion to odor of nonreward was not seen until Trial Block 6, or until the associated odorants had received 12 exposures to reward: (3) subjects increased production of odor of nonreward as a function of experience with reward, but after repeated exposure to the scent, escape subjects adapted: and (4) superior escape responding for Gp. E-NC(X) relative to that for E-NP(X) indicated differential odor excretion during extinction as a function of different acquisition schedules. The present data provided some support for the existence of a neutral odor and an odor of reward. In addition to the aversion demonstrated on early trials by E-nt, E-nt(X) demonstrated significant attraction on extinction Trials Blocks 4 and 8. The significant attraction shown by Gp. E-RP was the chief evidence for the existence of an odor of reward. The results were discussed in terms of the implications held for Amsel's frustration theory, future runway investigations of animal learning, and future research on pheromone communication in rodents.