No abstract

Five groups of rats were trained and extinguished in an 11 ft runway. Either 0, 10, 20, 30, or 40 trials were given with 1 Noyes pellet followed by the remainder of 40 trials with 10 pellets. The increase in response speed following the incentive shift was positively related to the number of I-pellet trials. Speed during extinction was monotonic with terminal acquisition speed. ProblemSpeed of response in the straight alley duringextinction has been found to be nonmonotonically related to the extent of training when a broad range of acquisition trials is used (lson, 1962; Clifford, 1964). Birch (1961) has attributed this result to the combined effects of goal anticipation and frustration. Theois & Brelsford (1964) account for the finding by hypothesizing that extinction is a positive function ofthe number of responses but a negative function of the strength of goal antiCipation. Under conditions where the total number of trials is held constant increasing strength of goal anticipation is expected to result in nonmonotonicity according to the former flosition and a monotonic negative relation according to the latter. The present experiment was designed to gain information on this point. The design also allows an evaluation of the change in response speed resulting f::om an increase in goal magnitude as a function of the number of preshift trials. Method.Seventy-five male hooded rats, about 90 days old at the beginning of training, were assigned equally to five groups. Three Ss, all from different groups, were eliminated because of illness. A 22-hr. food maintenance schedule was employed throughout the experiment with water always available. Each S was given one trial per day under 22-hr. food deprivation with the order of running randomized across Ss from day to day. Following a run S was returned to his individual home cage where he waited for a minimum of 30 min. before being fed for 1 hr.A straight runway, 4 in wide by 6 in high by 11 ft long, was constructed to be maximally homogeneous. The 1-ft starting section was designed without a door by using two wooden blocks so attached that S had to go under the first and over the second. S's start and running responses were timed by an arrangement of capacitance operated switches wherein S activated the timing device by stepping on copper plates, one of which was hidden under the start section and the other under the runway floor 4 ft down the alley.

AbstraetAfter they were weaned, albino rats were housed individually (Group 1), in pairs (Group 2), and in groups of five (Group 3). After 18 weeks of housing under these circumstances, the tendency toward gregariousness, defined as a function of the number of approaches to the other rat of the same species, was tested. Group 3 showed the strongest tendency toward gregariousness, Group 2 a weaker tendency, and Group 1 the weakest. Introduetlon Some research evidence (Denenberg, 1963;McClelland, 1956) has shown that the body weight and emotional behavior of rats are significantly influenced by their early experience. Other research evidence (Denenberg et al., 1964) has shown that the rat's behavior is affected by the postweaning social interaction with other organisms of the same species. One logical extension of these studies is to investigate the effect of postweaning social interaction of rats upon their tendency to approach another animal. The purpose of this study is to test the hypothesis that the tendency toward gregariousness is a function of rat's early experience in which the strength of such a tendency is positively related to the number of other rats housed together with the subjects in the homecage.

The heart rate (HR) of male hooded rats was recorded in a non home cage for three weeks. Then they were deprived of water (Group ], N = 6) or food (Group 2, N = 6) up to 96 h. HR was recorded at 8 h, 24 h, 48 h, 72 h, and 96 h of deprivation. The HR of Group 1 increased linearly with the duration of water deprivation, while that of Group 2 showed an inverse U-shaped function. These functions suggest that HR is influenced by two concomitant conditions: dehydration and metabolism.

The heart rate (HR) of male hooded rats was recorded in their individual home cages for three weeks. Then they were deprived of water (Group 1, N = 6) or food (Group 2, N = JO) up to 96 h. Immediately after the deprivation period water (for Group 1) and food (for Group 2) were placed in their home cages. Under these conditions, HR was recorded. During the deprivation period, the HR of Group 1 increased linearly with the duration of deprivation, and that of Group 2 showed an inverse U-shaped function. During the postdeprivation period, the HR of both groups sharply increased abou t 10 min after food or water was placed in their cages. These findings suggest that HR is clearly injluenced both by deprivation and by consummatory activities.