Runway performance of normal, sham, and anosmic rats as a function of magnitude of reward and magnitude shift

Abstract

A two-phase experiment was designed to yield information concerning the effects of magnitude of reward and magnitude shifts on the runway performance of normal, sham-operated, and surgically anosmic rats. Three squads of normal. sham, and anosmic subjects were each divided into three subgroups that received small. multiple-pellet large and single-pellet large reward, respectively, during the first phase (51 trials). During Phase II (30 trials), all subjects received the small reward. Reward magnitude effects developed during Phase I but were shown only by the normal and sham sUbjects. Significant depression effects were shown during Phase II by all subjects shifted from large to small reward. However, the form ofthe performance decrements shown during Phase II differed considerably between the normal and sham subjects and the anosmic sUbjects.Recent studies reported by Marrero, Davis, and Seago (1973) and Davis and Seago (1975) have been concerned with delineating the behavioral effects of rendering the rat subject anosmic. In both instances, the straight-runway apparatus was employed for testing purposes. The results of the Marrero et al. (1973) study in which reward magnitude (single-pellet large vs. single-pellet small) was manipulated indicated that magnitude effects were not shown by the anosmic subjects and further that the performance of the large-reward anosmic subjects was somehwat inferior (significantly so in the start measure) to that of the small-reward anosmic subjects.On the other hand, the Davis and Seago (1975) experiment studied the effects of anosmia on behavior in the differential conditioning situation. The results of this study indicated that differential responding failed to develop, thus suggesting, as did the Marrero et a1. (1973) study, that one effect of anosmia is to reduce incentive motivation. It is interesting to note that when the anosmic subjects were concurrently exposed to different reward magnitudes, as in the Davis and Seago (1975) Thus, the present experiment was designed to yield additional, and hopefully more complete, information on the effects of reward magnitude and reward magnitude reduction upon the runway performance of surgically anosmic subjects. During the first phase of the experiment, a factorial design employing three levels of reward magnitude (small, single-pellet large, and multiple-pellet large) and three olfactory states (normal, sham-operated, and surgically anosmic) was used. During the second phase of the study, all subjects received additional trials with the small-reward magnitude. Thus, the second phase constituted an incentive reduction phase for those subjects initially trained on large reward and was included to yield information concerning the effects of a successive, as compared with the simultaneous procedure employed by Davis and Seago (1975), shift in reinforcement. METHOD SubjectsThe subjects were 81 male albino rats purchased from the Sprague-Dawley Company, Madison, Wisconsin. Twenty-seven of the subjects were rendered surgically anosmi...

The partial reinforcement effect as a function of surgical anosmia

“…Moreover, the results of the Davis et al (1975) study indicated that the performance of anosmic subjects abruptly shifted from large to small reward declined gradually. This may be contrasted with the precipitous decrements displayed by normal and sham subjects in the Davis et al (1975) study and in other successive reward-shift studies (e.g., Crespi, 1942;Zeaman , 1949). On the other hand, the Davis and Seago (1975) report indicated that negative contrast effects typically found in differential conditioning studies (e.g., Ludvigson & Gay, 1967) employing normal subjects were not shown by anosmic subjects.…”

“…The results of these studies have suggested that one effect of rendering the rat subject surgically anosmic is to reduce incentive motivation . For example , performance differences between anosmic subjects receiving large and small reward magnitudes, respectively, failed to develop in both the Davis et al (1975) and Marrero et aL (1973) studies, while significant magnitude effects were shown by both normal and sham-operated subjects. Moreover, the results of the Davis et al (1975) study indicated that the performance of anosmic subjects abruptly shifted from large to small reward declined gradually.…”

“…For example , performance differences between anosmic subjects receiving large and small reward magnitudes, respectively, failed to develop in both the Davis et al (1975) and Marrero et aL (1973) studies, while significant magnitude effects were shown by both normal and sham-operated subjects. Moreover, the results of the Davis et al (1975) study indicated that the performance of anosmic subjects abruptly shifted from large to small reward declined gradually. This may be contrasted with the precipitous decrements displayed by normal and sham subjects in the Davis et al (1975) study and in other successive reward-shift studies (e.g., Crespi, 1942;Zeaman , 1949).…”

“…A recent series of studies (Davis, Harper, & Seago, 1975: Davis & Seago, 1975Marrero, Davis, & Seago, 1973) have concerned themselves with investigating the effects of surgical anosmia on behavior in the straight runway. The results of these studies have suggested that one effect of rendering the rat subject surgically anosmic is to reduce incentive motivation .…”

Reward magnitude effects as a function of within-day trial-by-trial analysis

“…In order to administer the relatively large number of training trials that appear to be required to produce the collapse or dissipation of reward magnitude effects, it is not uncommon to fmd that multiple daily trials have been administered (e.g., Davis, Harper, & Seago, 1975;McCain, Boodee, & Lobb, 1977;McCain, Lobb, & Newberry, 1976). Such trial-administration procedures may well produce a "warm-up" effect, with performance on the initial trial(s) being inferior to that shown on later trials.…”