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Discrimination learning in adult guinea pigs, Cavia porcellus

This is a research project I did for an animal behavior class in college, kind of my capstone project.
I used my guinea pigs in the experiment and they were not harmed in any way.

Abstract
Introduction
Method
Results
Discussion
References

 

Abstract

  The purpose of this experiment was to see if adult guinea pigs could learn to discriminate between left and right and between two different shapes. This study differs from others in that it uses a preferred food as a positive reinforcer while keeping the guinea pigs on a free feeding schedule compared to keeping the subjects on an 85% weight feeding schedule and using food as the positive reinforcer. It was predicted that the guinea pigs would learn the difference between left and right and the two different shapes. The results showed that they can learn to discriminate between left and right. However, they did not learn to discriminate between the two shapes. Possible reasons why this occurred may be the size of the criteria, the order in which the discrimination tasks were learned, and the fact that the same subjects were used in both tasks.

 

Introduction

    Guinea pigs, Cavia porcellus, are originally from the Andean Mountains in South America. They have been domesticated since at least the 1500s when Spanish explorers were first introduced to them by the native people (Lane-Petter & Porter, 1963). Since then, guinea pigs have been used primarily as laboratory animals. They were first used in biological studies, but have since undergone psychological experiments as well, the majority being studies of their social interactions or learning capabilities. They have also served as pets and as show animals.

       Poling and Poling (1978) did a two-part study on discrimination learning in guinea pigs to see if they responded similarly to other species. First, they taught the guinea pigs to press a lever with their nose. They were kept at an 85% free-feeding weight schedule. The guinea pigs were taught to respond to a lever in return for a reward. For pressing the left lever, they would receive a food pellet. Nothing happened when they touched the right lever. This led to an increased amount of left lever pressing. For the second part of the experiment, the guinea pigs’ behavior underwent extinction. If the left lever was presented and they touched it, no reward was given. The same happened for the right lever. Food was only given if the left lever was presented, but not touched. This resulted in less touches of the left lever. Their results found that guinea pigs do respond in a way similar to other animals, such as pigeons and ducks. They also wanted to show that guinea pigs do learn well while being deprived of food.

    A study keeping the guinea pigs at an 80% free-feeding weight taught them to press a lighted button with their nose (Petersen, Prosen, Moody, & Stebbing, 1977). They pressed the lit right button when they heard a tone and received a pellet. If they pressed the button when there was no tone, then the lights in the testing box were shut off for 15s. The 11 guinea pigs were tested for up to 150 min. at a time and earned between 200-300 food pellets.

    In another experiment, adult guinea pigs were taught to press a lever after being deprived of food for 23 hours (Angermeier, McLean, Minvielle, & Grue, 1987). For each lever touch they received one pellet. They were tested for one hour a day or until earning 50 pellets. Fifteen of the sixteen guinea pigs learned this task. They found that guinea pigs are similar to other animals in the amount of rewards needed to learn and in the number of animals that successfully learn the task.

    Water deprivation was also used to stimulate guinea pigs to learn (Collier, Levitsky, & Weinberg, 1968). Twenty-three guinea pigs were taught to bar press for water. They were fed ad lib., but were given no water except when bar pressing. Once deprived of water, the guinea pigs ate less and quickly lost weight. The experiment consisted of three cycles of water deprivation and recovery. Nine guinea pigs died throughout the course of the experiment.

    As shown, the predominant way to treat guinea pigs in learning experiments has been to keep them on an 85% free-feeding weight schedule (Poling & Poling, 1978). Others have tried water deprivation, but have had little or no success (Collier, Levitsky, & Weinberg, 1968). They found that guinea pigs do not adapt well to water deprivation and die within a few days. Researchers have had difficulties finding a suitable way to test guinea pigs (Jonson, Lyle, Edwards, & Penny, 1975). They have taken the style used for testing rats and directly applied it to guinea pigs without taking into full consideration the differences that might occur between the two types of animals.

    Berryman (1974) has had success keeping the guinea pigs on a free feeding schedule and using a preferred food as a positive reinforcer. She used a mixture of dried milk and cereal for babies with water. The guinea pigs were given a minute amount. They were able to consume a lot of this mixture without becoming satiated as did guinea pigs given other reinforcers (Gundy, 1959). Gundy (1959) used carrot juice as the reward. He had 0.25cc available to the guinea pigs for 4s. However, the guinea pigs could take only 30–60 reinforcers per hour compared to the 300 using Berryman’s mixture (Berryman, 1974). For efficiency, Jonson et al. (1975) recommend using liquid reinforcers over solid food as guinea pigs are rather slow eaters.

    The purpose of this study is to teach adult guinea pigs to discriminate on two criteria, left and right, and between two different shapes, a circle and a triangle, in return for a preferred food reward. An adult is defined as being 6 months or older. The hypothesis is that they will be able to learn the difference between left and right and between the two shapes.

    The implication of this study is to show that guinea pigs can learn to discriminate between two criteria for a preferred food reward on a free feeding schedule. This would show that guinea pigs no longer need to be deprived of food or water by being kept on a percent weight feeding schedule or water deprivation schedule.

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Method

Subjects

Three adult guinea pigs, Cavia porcellus, that are pets of the researcher were tested in this experiment. They are all approximately 1 year old and weigh between 1000-1400 g. There are two males and one female. Each of them is housed separately. They were kept on a free feeding schedule throughout the experiment, being fed L’Avian guinea pig food. They also had water ad lib. They were tested at room temperature, 21 degrees C.

Materials

Each guinea pig was tested in a wooden box (29 x 44 x 29 cm) that had a slit (5 x 1.5 cm) in one side that was 5 cm above the bottom of the box. The items used for the guinea pigs to distinguish between left and right were two rectangle pieces of cardboard (3 x 4 cm). The two different shapes were a circle and a triangle cut out of cardboard, also of similar proportions. These were hung with rope over the side of the box so as to be nose level (7 cm above the ground). As a positive reinforcer for touching the correct side/shape, they were hand-fed a tiny piece of sweet potato through the slit in the side of the box.

Procedure

The guinea pigs were tested separately, one after the other. They were tested at a time when the experimenter noticed that they were eating, ranging from 2:00 p.m. to 1:00 a.m. This would ensure that the guinea pigs were hungry and would work for a preferred food. Two pieces of cardboard were hung over the side of the box, either two identical rectangles or a circle and a triangle. For the first part of the experiment, the guinea pigs were shown the two rectangles. They had to touch the left one with their nose in order to receive a reward, the sweet potato. If they touched the right one, nothing happened. The testing took place for twenty minutes each day. The daily testing went on until the guinea pigs touched the correct item 90% of the time.

For the second part of the experiment the guinea pigs were placed in the box as before, but were given two different shapes to distinguish between, a circle and a triangle. When they touched the circle with their nose, they received the reward. They received nothing for nosing the triangle. Part two had the same expected level of 90% correct responses.

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Results

For part one, the criterion of 90% correct was met on day 4, but testing was continued for two more days to ensure stability of results. The mean percent of correct responses ranged from 60.0% on day 1 to 96.4% on day 6 (see Figures 1 and 2).

The 90% criterion was not met for the shape discrimination task. No significant learning occurred in being able to differentiate between the circle and the triangle (see Figures 3 and 4). The mean percent of correct responses was higher at day 1 than at day 6.

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Discussion

The hypothesis of this experiment was that adult guinea pigs would be able to learn to discriminate between left and right and between two different shapes in return for a preferred food reward. The data show that the guinea pigs did learn the difference between left and right, but not between the two shapes.

The original length of each testing session was to be thirty minutes. However, that turned out to be too long of a time, as the guinea pigs had to urinate by then and were distracted. The time was then lowered to twenty minutes. This worked, but it also seemed to be too long. After about 15 minutes, the subjects would turn away from the testing side and explore the rest of the box, including the right criterion. They did not seem to be nosing it in order to get a treat because they did not come to the feeding hole after touching it. This brings up a problem related to the testing material, cardboard. The cardboard seemed to be a preferred food in itself. However, once they learned that they could get a preferred food, chewing on the cardboard declined. In contrast to the suggestion of Jonson et al. (1975) of using liquid reinforcers because guinea pigs eat slow, the small pieces of sweet potato worked better than attempting to reward them with juice through a syringe.

In part one of the experiment, subject 2 had less correct responses than the other subjects on day 3, possibly due to the time at which he was tested. He had been eating when he was started testing, but it was in the middle of the afternoon, which is not a main feeding time, so he may not have been very hungry.

The results of part two of the experiment may have been confounded by the order in which the discrimination tasks were learned. The guinea pigs learned to differentiate between left and right very quickly, so when they began the second part of the experiment, they kept touching the left shape because that had previously meant a reward. If the shape discrimination had been taught first, they may have been able to learn it, as they would not have previous information to distract them. Another, and better, way to get rid of this confound would be to use a different set of subjects for each task. The size of the criterion may also have been a problem. With their eyes located on the side of the head, instead of in the front, it may have been difficult for them to tell the difference between the two shapes so close up. Bigger shapes may have helped ease this problem.

This experiment shows that adult guinea pigs can learn a discrimination task when rewarded with a preferred food. However, the difficulty level of the shape discrimination task may have been too much. The fact that the same subjects were used in both tasks, may also have been a confounding variable. What the data does show, is that guinea pigs do not need to be deprived of food or water in order to be successfully motivated to learn.

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References

Angermeier, W. F., McLean, J., Minvielle, D., & Grue, C. (1987). Food-rewarded operant learning in the guinea pig. Bulletin of the Psychonomic Society, 25, 292 - 295.

Berryman, J. (1976). Operant conditioning in non-deprived guinea pigs. Journal of the Experimental Analysis of Behavior, 25, 400.

Collier, A., Levitsky, D., and Weinberg, C. (1968). Body weight loss as measure of motivation in thirsty guinea pigs. Psychonomic Science, 10, 27-28.

Gundy, R. F. (1959). Some techniques in operant conditioning of the guinea pig. Journal of Experimental Analysis of Behavior, 2, 86.

Jonson, K. M., Lyle, J. G., Edwards, M. J., and Penny, R. H. C. (1975). Problems in behavioral research with the guinea pig. Animal Behaviour, 23, 632-639.

Lane-Petter, W., and Porter, G. (1963). Guinea-pigs. In W. Lane-Petter (Ed.), Animals for Research: Principles of Breeding and Management (pp. 287 – 324). London: Academic Press.

Petersen, M. R., Prosen, C. A., Moody, D. B., and Stebbing, W. C. (1977). Operant conditioning in the guinea pig. Journal of Experimental Analysis of Behavior, 27, 529-532.

Poling, A., Poling, T. (1978). Automaintenance in guinea pigs: Effects of feeding regimen and omission training. Journal of Experimental Analysis of Behavior, 30, 37 - 46.

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Figure Captions

Figure 1. Individual correct responses for discriminating between left and right.

Figure 2. Mean correct responses for discriminating between left and right.

Figure 3. Individual correct responses for discriminating between two different shapes.

Figure 4. Mean correct responses for discriminating between two different shapes.

Figures to be added soon.

 

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