Free-choice Trials Research Articles

Retroactive interference in rats: independent effects of time and similarity of the intervening event with respect to acquisition.

Events occurring during the retention intervals for a 5-min delayed alternation task were used to investigate the factors that influence retroactive interference. Appetitive reinforcement in an E-maze was employed to train rats on the delayed alternation task consisting of a forced-choice (target event) trial followed by a free-choice (test) trial. Occasional probe trials added a potentially interfering event either at the beginning, middle, or end of the retention period. These events also varied in similarity to the target events, ranging from low similarity to the converse of the target event. Interference increased both with the interval between the target and intervening events and with the similarity between the converse of the target event and the intervening event; however, there was no tendency, significant or otherwise, towards an interaction between stimulus similarity and the interval between the target and intervening events. Control groups demonstrated that the interference was of an associative nature and that the interval between the intervening event and the test trial was little consequence. These results are discussed in terms of two separate types of interference: similarity interference which depends on stimulus similarity of the intervening event to the converse of the target event but not on the temporal location of the intervening event, and processing interference which depends on the temporal location of the intervening event but not on its similarity to the converse of the target event.

Laboratory Efficacy of Some Commercial Zinc Phosphide Baits Used for Control of Meadow and Pine Voles in Orchards1

Abstract Five commercially available zinc phosphide (Zn3P2) preparations were tested in a 3-day, free choice trial for efficacy on meadow voles (Microtus pennsylvanicus) and pine voles (M. pinetorum). A 2% Zn3P2 pellet produced a significantly greater and quicker kill in meadow voles than a 2% Zn3P2 oat-corn bait. Whole oat and cracked corn baits (2% Zn3P2) performed as well on meadow voles as did a 1% Zn3P2 paraffinized pellet. The 2% Zn3P2pellet produced significantly greater mortality in pine voles than did 2% Zn3P2 oat-corn and whole oat baits and a 1 % paraffinized pellet. There was no evidence that grain baits were more effective for meadow voles than pine voles.

Chronic Toxoplasma infections and familiarity-novelty discrimination in the mouse.

Male mice were exposed to a black arm and the stem of a Y-maze; entrance to a white arm was blocked by a transparent door. Toxoplasma-infected mice were significantly less active and tended to produce fewer faecal boluses than uninfected controls. In a subsequent free-choice trial, in which both arms were black, the uninfected mice spent significantly more time in the novel (previously blocked) arm; the infected mice showed no preference for either choice arm. Possible explanations are discussed. In particular, it seems that Toxoplasma-infected mice may be less responsive to novel stimuli. This suggestion has important implications for our understanding of one of the major ways in which Toxoplasma passes from host to host. If Toxoplasma infections impair responsiveness to novel stimuli, then infected mice are more likely to be taken by predators.

Preference for punishment of the instrumental or the consummatory response

In two discriminable runways, rats were punished (shocked) either prior to receiving water reinforcement (punishment of the instrumental response) or after ingesting the water (punishment of the consummatory response). Both forced-choice and free-choice trials were conducted. Results indicate that rats preferred to have the instrumental response punished. It was also observed that the subjects more frequently failed to traverse the runway in which the consummatory response was punished compared to the runway in which the instrumental response was punished. The results were interpreted as being consistent with predictions derived from net incentive theory.

Incentive preference as a function of water deprivation and locus of discriminative stimuli

Water-deprived rats (23.5 and 18 h) acquired simultaneous discrimination tasks with position of the positive stimulus paired with water and 20% sucrose. Free-choice trials with S+ simultaneously present at both positions occurred following discrimination acquisition. Animals acquired tasks in which either goal-door and/or floor-texture cues were relevant. All moderately deprived discrimination groups displayed more errors and slower speeds to S+ at the water than at the sucrose side. Only highly deprived animals that acquired a floor-texture discrimination developed similar, but not as great, speed differences. Such speed differences were due to increased speeds to S+ at the sucrose position. All but the highly deprived floor + door learners displayed reliable free-choice sucrose preferences. Moderately deprived animals tended to display greater sucrose preferences than highly deprived animals. Results were discussed in terms of attention and learning as a function of deprivation level. Experiment 1 in the present study was based on a thesis submitted by the second author in partial fulfillment of the requirements for a master’s degree at the University of Windsor. The present report is based on a paper delivered at the Canadian Psychological Association meeting, Quebec City, Quebec, June 1975. The authors wish to thank Dr. R. C. Beck of Wake Forest University, Winston-Salem, North Carolina, for his valuable suggestions on the manuscript.

Incentive preference under two levels of water deprivation in the rat

Rats under high (23.5 h) or moderate (18 h) water deprivation were required to learn a simultaneous goal door discrimination with S+ position correlated with incentive (water and 20% sucrose). A series of free choice trials with S+ simultaneously present at both incentive positions followed the initial discrimination. Moderately deprived animals made more errors and ran more slowly to S+ when it occurred on the water side than when on the sucrose side during discrimination trials. Highly water-deprived animals displayed less consistent and less differentiated speeds between incentives. Both deprivation groups preferred sucrose to water on free choice tests, but only moderately deprived animals tended to exclusively choose sucrose. The results were interpreted as indicating that the two deprivation levels substantially created different thirst arousal conditions in the animals.

Influence of female's sexual cycle on aggressiveness in male rats.

Two experiments examined the relationship between the female's stage of estrus and agonistic behavior among males. Socially subordinate male albino rats were exposed to an inaccessible female and then given equal numbers of free-choice and forced-choice trials to a more aggressive "target" male or to an empty compartment. The submissive males were more aggressive following exposure to an estrous female than following exposure to a diestrous female. Furthermore, the probability of approaching the more aggressive male increased. This heightened level of aggressiveness was accompanied by a comparable increase in hostile behaviors by the dominant target males of Experiment 1. However, in the second experiment the increase in submissive-male aggressiveness was sufficient to reduce the social distance between the submissive subjects and their moderately aggressive target males.

Spontaneous alternation as a function of number of forced-choice responses in the goldfish (Carassius auratus)

This experiment assessed the role of the number of forced-choice trials on spontaneous alternation in the goldfish. Goldfish were forced to the preferred reinforced arm of a T-maze for 1, 5, 7, 10, or 15 trials. Following these forced-choice trials, the direction of turn on a free-choice trial was recorded. The likelihood of alternation was found to be a function of the number of previous forced-choice trials. The similarity of the functional relationship found in this experiment was related to that found in similar experiments using other species as Ss.

Effect of Achievement Motivation and Social Environment on Risk Taking

Abstract The effects of achievement motivation and competitive environment on the risk taking choices of Ss performing a motor task were investigated. Fifty achieve success Ss and 50 avoid failure Ss (selected by the French Test of Insight and the Test Anxiety Questionnaire) practiced a modified shuffleboard task from which empirical probabilities of success were found for each S. Ss were randomly placed into 1 of 5 competitive treatment levels—alone, presence of others, interpersonal competition, intergroup competition, and interpersonal and intergroup competition. Each S was given 20 free choice trials. Achieve-success Ss perferred intermediate risk choices to a significantly greater extent than avoid failure Ss and supported risk taking theory. Avoid failure Ss also preferred extreme risk choices to a significantly greater extent than low or intermediate risk. No competitive treatment effects were noted.

Forgetting of lateralized engrams studied by interhemispheric conflict in rats

Functionally hemidecorticate rats were trained in a simple T maze with the right hemisphere to go right and 24 hr later with the left hemisphere to go left. In five free-choice trials performed in the same T maze with both hemispheres intact, equilibration of right and left choices was found on Day 3, when 9/10 avoidances + 30 overlearning trials to the right (Day 1) were followed by 3/3 escapes to the left (Day 2). Equilibrated choice behavior on Days 4 and 5 was achieved in other groups by increasing the learning criterion on Day 2 to 5/6 and 9/10 escapes, respectively. Control groups trained only the first or the second habit chose the right or left side, respectively, whereas rats learning the two tasks sequentially with the whole brain showed preference for the last habit. Percentage of left choices on Days 3–5 was significantly increased when rats trained under the equilibrated choice conditions were subjected with intact brain 2 hr before the second hemidecorticate training to a stressful experience (20 min swimming). The assumption is made that the equilibrated choice reflects equal strength of the lateralized antagonistic engrams at the time of retention testing. The forgetting function derived from the experimental data cannot be described by a simple exponential curve but is negatively accelerated in time.

Time labelling of independently acquired lateralized engrams in rats

Functionally hemidecorticated rats were trained with the right hemisphere to go right and 24 hr later with the left hemisphere to go left in a simple T-maze. In 5 free choice (FC) trials performed with intact brain on Day 3 equilibration of the right and left turns (40% FC left) was found when 9 10 avoidance + 30 overtraining trials to the right were followed by 3 3 escapes to the left. Control groups trained only in the first or the second habit chose the left arm in 15% and 73%, respectively, whereas intact rats learning the two tasks sequentially displayed a marked reversal (83% FC left). When rats trained under the above equilibrated choice conditions were subjected with intact brain two hr before the second hemidecorticate training to a strong emotional experience (20 min swimming), the percentage of left choices was significantly increased on Day 3 (70% FC left). Swimming neither interfered with retention of the isolated first engram (20% FC left) nor improved the acquisition of the isolated second engram (65% FC left), but when inserted between two lateralized learning sessions with opposite hemispheres it increased the weight of the second experience to the level found in reversal learning. Similar results were obtained with a water T-maze when using foot shocks (30 min) as reference. A hypothetical model is proposed explaining the absence of relative time labelling of lateralized engrams and the possibility to restore it by the bilaterally recorded reference event, bridging the gap in the hemispheric memory records.

Aversive stimulation and rats’ preference for familiarity

Hooded rats were confined in the stem of a T-maze in which glass doors prevented access to black-white choice arms. On a subsequent free choice trial, when both arms were either black or white, rats shocked prior to choice spent a greater amount of time in the unchanged arm, whereas unshocked controls preferred the changed arm. It was suggested: (1) that the results provide firm support for the hypothesis that aversive stimulation elicits a shift in preference toward familiarity; (2) that the behavior of shocked laboratory rats in this type of situation may be akin to the “neophobia” observed in wild rats.

Effect of Achievement Motivation and Social Environment on Performance of a Motor Task

The effect of achievement motivation and social environment on a motor task was investigated. 50 achieve-success Ss and 50 avoid-failure Ss (selected by the French Test of Insight and the Test Anxiety Questionnaire) practiced a modified shuffleboard task from which empirical probabilities of success for task performance were found for each S. In the performance phase Ss were randomly placed into one of 5 treatments - neutral, presence of others, interpersonal competition, interpersonal cooperation, interpersonal competition and intergroup competition. Ss were made aware of the scoring system and given 20 free-choice trials. Achieve-success Ss performed significantly better than avoid-failure Ss in the practice phase. No differences were found for achievement motivation in the performance phase. Social environment did not affect performance or interact with achievement level of Ss.

ELECTRIC SHOCK AND RATS' PREFERENCE FOR THE FAMILIAR ARM OF A MAZE

Hooded rats were habituated to one arm and the stem of a T‐maze while being able to observe the other arm through a glass door (one arm was black and the other white). In a subsequent free choice trial when both arms were of similar albedo to the habituated arm fewer shocked than unshocked rats chose the novel arm. During an observation period following initial choice it was found that shocked rats spent significantly more time in the habituated arm.

Effects of Percentage of Reinforcement upon Behavioral Contrast in the Rat

A large amount of data has been reported in recent years concerning the interaction of a given condition of reinforcement and previous or contemporary conditions of reinforcement. This interaction has been commonly referred to as “behavioral contrast”. In this paper, it was tested whether the contrast effect was obtained in the discrete trial situation in terms of running behavior and behavior variability.Of two experiments reported here, Exp. I was concerned with simultaneous contrast effect, while Exp. II with successive contrast effect. The apparatus used was one pair of T maze. Except a start box and goal boxes, one maze was painted white (S1) and the other black (S2). A start box and goal boxes were painted gray in both mazes.In Exp. I, Ss were randomly assigned to five groups of 10, each. The groups, defined in terms of the percentage of reinforcement administered in their positive and negative mazes, respectively, were; Group I (100%-100%), Group II (100%- 50%), Group III (100%-0%), Group IV (50%-50%), Group V (50%-0%). After exploration and pretraining, all Ss were given 21 successive free-choice trials per day in two T mazes for 10 days.In Exp. II, Ss were divided into four groups of 10, each. The groups were; Group I (100% control), Group II (100% downshift), Group III (30% control), Group IV (30% upshift). During first 5 days of training, Groups II and IV received identical treatment with Groups I, III, respectively. Subsequently in Group II, percentage of reinforcement of S2 were shifted from 100% to 30% during Days 6 to 15. On the contrary, Group IV received upshift of S2 from 30% to 100%.Three response measures were employed in both experiments, i. e., starting latency, running time and choice direction.The results were as follows : 1) In Exp. I, the result of starting latency indicated a significant evidence for the positive contrast effect. That is, the starting latency in the 100% maze was shortest for Group III, intermediate for Group II and longest for Group I (Fig. 1). Though there was statistically no difference among 3 groups in running time, the similar tendency was found.2) The choice behavior significantly differed among 5 groups. Although Groups I and IV tended to chose the same side with about equal frequency at the end of training, the Ss subjected to the differential conditioning (Groups II, III and V) preferred one side in 100%, maze and avoided that side in, the other maze (Fig. 2). This fact would suggest that some difference in percentage of reinforcement tends to fixate the choice behavior and these tendencies result from behavioral contrast effect.3) Unlike Exp. I, Exp. II showed no evidence of contrast effect. The successive shift of percentage reinforcement of S2 did not result in any change in response time (Fig. 3) and choice behavior. It would be shown from the present experiments that behavioral contrast effect was observed in the simultaneous shift of percentage of reinforcement, but not in the successive shift.

Maze Path Selection in the Turtle (Chrysemys): A Quasi-Comparative Study

5 fresh water turtles (Chrysemys) were run in each of 4 groups in a maze containing 3 different length pathways: long (108″), medium (84″), and short (60″). Subjects in Group I had 16 free choice trials. Subjects in Groups II, III, and IV were given 16 forced choice trials to the long, medium, and short pathways respectively, followed by 16 free choice trials.

Spontaneous alternation and induction

Previous studies have shown an induction phenomenon, i.e. a considerable decrement in the variability of behavior and a facilitation of its running response, in the semi-circular maze when reinforcement was presented after or between nonreinforced trials. The present series of experiments were designed to test whether or not a similar effect would be shown in a T-maze, and to determine what kind of stimulus was used as a cue for choice. For these purposes, percentages of spontaneous alternations and the running time were measured during the conditioning, extinction, and reconditioning periods.Experiment I: Thirty-three hungry rats were divided equally into three groups: Group 0, Group 11, Group 41. After exploration and pretraining, all Ss were given 11 successive free-choice trials per day for 4 days in the T-maze (the conditioning period). All choices were rewarded during this period. On the following day, Group 0, Group 11 and Group 41 received 0, 11 and 41 successive nonreinforced trials respectively (the extinction period), and then all Ss were given 11 reinforced trials (the reconditioning period).The percentage of alternations was significantly higher than chance level during the conditioning period. However, the greater the number of nonreinforced trials during the extinction period, the significantly greater the decrement of alternation in percent and the facilitation of running time during the reconditioning period. From these results, it might be concluded that a similar induction phenomenon was found in the T-maze as was in the semi-circular maze.Experiment II: Eighteen hungry rats were divided equally into two groups (Group Exp. and Group Cont.). After exploration and pretraining, all Ss were given 11 successive free-choice reinforced trials per day for 4 days in a cross-maze with a black arm and a white arm (the conditioning period). On a half of any two consecutive trials, they started from the same starting boxes, and on the other half trials, they started from the opposite starting boxes. Immediately after 41 nonreinforced trials, Group Exp. was given 11 reinforced trials. The Group Cont. did not receive any nonreinforced trial. From the data on their spontaneous alternations, it would be concluded that Ss alternated their choices on the exteroceptive cues during the conditioning period. The Group Exp. showed the dramatic decrement of alternation in percent during the reconditioning period. Their choices were also based on the exteroceptive cues. The running responses of the Group Exp. during this period were significantly faster than the ones of the Group Cont..

Effects of forced reward-nonreward ratios on children's performance in a discrimination task

A study was run to determine if correct responses and response speeds on free choice trials would vary with changes in the ratio of rewarded to nonrewarded ( R N ) forced trials in a two-stimulus discrimination learning task. The Ss were 112 3- to 5-year-old children. The task involved learning to select the correct 1 of 2 differently colored cars and rolling it down a runway. Four blocks of 6 forced trials were interspersed among 4 blocks of 4 free choice trials. Sixteen Ss were randomly assigned to each of the following forced trial block R N groups: 0 6 , 1 5 , 2 4 , 3 3 , 4 2 , 5 1 , 6 0 . Substantiating previous findings, correct responses were an inverse linear function of the size of R N . While R N groups did not differ significantly in their response speeds on free choice trials, Ss did respond faster on forced than on free choice trials, particularly among the intermediate R N groups (i.e., 2 4 , 3 3 , 4 2 ).

Infantile Handling, Method of Goal Box Removal, Stimulus Complexity, and T-Maze Performance

A comparison was made between the running-speed scores and choice behavior of Ss which had been handled from Days 1–21 and their nonhandled litter mates. When they were 60 days old, Ss were food deprived and were tested in a T-maze. They were given four free choice trials each day over a 14-day period, and were rewarded regardless of their choice of goal boxes. One subgroup was removed by hand whenever Ss entered the striped goal box and were removed by a transport box if they entered the gray goal box. Another subgroup received the opposite treatment. Results indicate that handled rats showed faster running speeds than the nonhandled Ss and that both groups showed a systematic increase in running speed with successive test days. The choice behavior data indicates that both handled and non-handled Ss showed no systematic preference for the method of goal box removal nor for the stimulus complexity of the goal box.

Pre-exposure and stimulus choice: Effects of odor trail

Rats pre-exposed in one arm of a T-maze enter the other arm on a subsequent free choice trial. It is possible that the odor-trail avoidance tendency reported by Douglas accounts for this phenomenon. The present experiment, however, found no effect on the phenomenon from presence or absence of the rat’s own odor trail.