Neophobia

Abstract Using rats in a cross - fostering design, we examined the effects of pre - and post - weaning rearing environments on feeding neophobia, open field activity, runway training, and visual discrimination learning. Fostering had no effect on the offspring behaviors. The animals reared, post - weaning, in an enriched environment consumed more food in a novel situation, were less active in the open field, and learned the first of two discrimination tasks faster than did the animals reared in the standard condition. Inter - correlations among these measures were nonsignificant, suggesting that the effect of environment on learning cannot be reduced to temperamental factors. The deficit in learning resulting from rearing in standard environment does not, however, appear to be irreversible; animals reared in the standard condition reached performance levels on the second discrimination task characteristic of those reared in the enriched environment.

During the 20th century, the question of the degree of the heritability of numerous behavioral patterns and abilities has been an intensely contested issue in psychology. Although the most fervent debates have focused on the collection, analysis, and interpretation of human data, animal research, with its advantage of experimental control, has made significant contributions to our understanding of the origins of individual differences.

Hebb (1947) initiated a line of research examining the behavioral consequences of rearing rats in different post - weaning environments. Since then, researchers have found that rats socially housed in enriched environments containing a variety of manipulable objects have consistently performed better on learning tasks, such as the Hebb - Williams maze, than have those reared in standard conditions in conventional individual laboratory cages. Diamond (1988) and Rosenzweig and Bennett (1976) have provided substantial reviews of the extensive literature on the effects of enrichment on the brain and behavior.

Since the earliest enrichment studies, investigators have sought to determine whether the positive effects of enrichment on learning were direct or were the indirect consequence of more general temperamental traits. It has frequently been alleged that the slower learning rates of animals reared in standard conditions can be accounted for in terms of general activity level. But the findings have been contradictory and the interpretations equivocal. On the one hand, animals reared in standard conditions have been found to exhibit a fear - like response and, in general, lower levels of activity (Hatch, Balazs, Wiberg, & Grice, 1963; Luchins & Forgus, 1955). This lower level of activity has been proposed as an explanation for their poorer maze - learning performance (Myers & Fox, 1963); the less animals explore the maze, the longer it will take them to learn where the food is located. In contrast, other researchers have found animals reared in standard conditions to be more active in general, and have offered a "hyperactivity" interpretation of their diminished maze learning capabilities (Zimbardo & Montgomery, 1957). Explanatory accounts of differential learning have had it both ways: Animals either lack sufficient exploratory behavior or they explore to excess. More recently, Holson, Scallet, Ali, and Turner (1991) argued that this apparent contradiction was, at least in part, the result of an interaction between prior handling and rearing environment. Without prior handling, there were no open field activity differences between those rats reared in standard conditions and those reared in enriched conditions. With prior handling, however, rats reared in standard conditions were substantially more active than their counterparts.

General activity level has not been the only mediating temperamental trait used to explain differences in learning. Holson (1986) found that the open field activity of rats reared in standard conditions was no different from that of their enriched counterparts. Although, as expected, the enriched rats entered the goal box in a maze more frequently than did those reared in standard conditions, the pattern of errors suggested to Holson that the rats reared in standard conditions were actively avoiding the goal box rather than having difficulty finding it. Holson concluded that what were thought to be learning differences were actually differences in the animals' degree of feeding neophobia - their unwillingness to feed in a novel surrounding. Rats reared in standard conditions were more neophobic.

Our study had two purposes. As our primary objective, we orthogonally manipulated cross - fostering and enrichment to examine their independent effects on feeding neophobia, open field activity, runway training, and learning. Rather than using performance on a maze to assess learning, we used two simple visual discrimination tasks. Such tasks have also been found to be sensitive to rearing environment (Greenough, Yuwiler, & Dollinger, 1973; Meier & McGee, 1959). These tasks have the advantage of minimizing the effects of activity and feeding neophobia, and also do not require the complicated scoring and interpretive baggage of a complex maze.

Consistent with our secondary objectives, cross - fostering affords the opportunity to explore genetic and other direct biological effects: the effects of biological and nursing dam.(f.1) The work of Tryon (1940) and Thompson (1954) demonstrated that maze - bright rats could be selectively bred, suggesting that differences in genotype were, at least in part, responsible for individual differences in learning rates. As with the enrichment studies, an alternate interpretation, focused on temperamental factors, was quickly offered. Searle (1949) found that maze - bright rats had a stronger "hunger drive," a lower level of general activity, and a greater running speed. Thus, researchers may have been selecting animals for genotypes associated with these indirect temperamental and psychomotor factors rather than for genotypes associated with more direct cognitive factors. Further complicating matters, Cooper and Zubek (1958) found that although maze learning could be selectively bred, it was also highly influenced by rearing environment.

METHOD

Subjects

Ten timed - pregnant outbred Long - Evans rats were purchased from Charles River Breeding Laboratories. The outbreeding to rats obtained from other breeding laboratories, such as that carried out by Charles River Canada, ensures some measure of genetic variability in the stock. All dams gave birth within a 36 - hour period. Immediately following the birth of the final litter, half of the male pups and half of the female pups from each litter were randomly cross - fostered to other dams, with the constraint that only one male from a given litter could be distributed to any given fostering dam. Litters were culled to 10 pups, 6 plus or minus 1 males. All litters were monitored regularly for the 24 hours following cross - fostering for any signs that a dam might be rejecting her fostered offspring.

Dams and their litters were housed in 45 x 24 x 20 cm polypropylene litter cages with Beta Chip contact bedding. The cages were covered with stainless steel wire lids and lodged in a room kept at 22degree C on a 12:12 hour light - dark cycle. For identification purposes, the lower backs of all pups were marked, using a three - band code applied with nontoxic colored markers. This required handing all animals on a daily basis until postnatal day (PND) 15, when the ears of the male pups could be notched.

On PND 23, all pups were weaned and post - weaning rearing environment assignments were made. Four male pups were randomly selected from each litter, two of each dam's biological offspring and two of each dam's fostered offspring. One of the biological and one of the fostered offspring were assigned to the standard post - weaning condition and one of each was assigned to the enriched rearing condition, with restrictions on randomness ensuring that two pups from each biological litter were assigned to the standard and two to the enriched condition. This meant that four biological offspring of each dam were included in the study: two she had nursed and two that had been fostered out, with one of each assigned to the enriched condition and one of each assigned to the standard condition. Following the assignment of pups, all dams were housed individually in standard cages with food and water provided ad libitum.

Post - Weaning Rearing Conditions

There were two post - weaning conditions: standard and enriched. The 20 pups in the standard condition were individually housed in 18 x 24.5 x 27 cm stainless steel wire - mesh cages. These cages were hung on a single rack such that the animals could smell and hear but not see each other. Feeding and drinking were ad libitum. In an adjacent room of the same size, the 20 pups in the enriched condition were housed in two groups of 10. Each group was housed in a row of three interconnected 55 x 55 x 36 cm stainless steel wire - mesh cages joined by 12 cm long tunnels. Although food and water were available ad libitum, the location of the food and water was changed daily, placed randomly in only one of the three cages. Additionally, ramps, balls, bells, and activity wheels were placed in the cages and replaced or repositioned daily. Enriched pups were also exposed to a variety of visual and auditory stimuli: A radio was placed on alternating 24 hour cycles and the outsides of the cages were decorated with 19 x 24 cm sheets of black and white paper, some solid color, some half white and half black, and some with vertical, horizontal, or diagonal stripes. These sheets of paper were also randomly changed or repositioned daily. Thus, we hoped to maximize the enrichment effect, given that both social rearing and complex environments have been shown to influence behavior (Sirevaag & Greenough, 1988). The 12:12 hour light - dark cycle was maintained for both the standard and the enriched offspring.

During the 45 days the animals were in the post - weaning rearing environments, human contact was minimized. One of the experimenters or a technician entered both rooms daily to visually inspect the animals and to ensure that food (Laboratory Rodent Diet 5001, PMI Feeds Inc.) and water were available and repositioned for the enriched animals. Litter pans connected to the underside of the cages were changed twice a week. Only animals appearing to be ill or injured were directly handled for examination.

Procedure

On PND 68, the 20 enriched pups were transferred to standard housing conditions identical to those of their standard - condition littermates. The following day, all 40 pups were placed on a 23 - hour food deprivation schedule and handled daily for 5 minutes prior to their 1 - hour ad libitum feeding. Throughout all subsequent testing, the pups were maintained on a 23 - hour food deprivation schedule and handled for 1 min prior to each test.

On the seventh day of food deprivation (PND 75), the animals were weighed and tested for feeding neophobia. After each animal was removed from the testing cage, it was returned to its home cage and given its 1 hour of ad libitum feeding (Laboratory Rodent Diet 5001). On the following day (PND 76), the animals' open - field activities were recorded. On PND 83, the animals were weighed again, and feeding neophobia testing was repeated. Again, on the following day (PND 84), open - field activity was recorded. Two days later (PND 86), testing of all animals began on the black - white discrimination task. Each animal began the vertical - horizontal stripes discrimination task the day after its completion of the black - white task. The researchers were blind to the animals' post - weaning condition during all testing sessions.

All testing began at 8:00 a.m. and was conducted in an adjacent room to which animals were transported individually in their home cages. Littermates were tested consecutively and always in the same order until criterion on the final task was reached.

Once all pups completed testing on the second discrimination task, the dams were placed on a 23 - hour food deprivation schedule and handled 5 minutes daily. Dams were then tested on the same set of procedures as their offspring: feeding neophobia, open field activity, runway training, and visual discrimination.

Again, all testing began at 8:00 a.m. and was again conducted in a neighbouring room to which dams were transported individually in their home cages. The dams were tested successively and always in the same order until criterion on the final task was reached.

Behavioral Tests

Feeding Neophobia. To test their willingness to feed in a novel environment, animals were placed for 10 minutes in a white polypropylene cage (30 x 24 x 18 cm) containing a glass petri dish filled with a sweet breakfast cereal. Thus, both the food and the situation were unusual for the animals. The food was weighed before the animals were put into the cage and after they were removed, the difference in weight being the amount of food consumed. During the 10 - minute testing period, the experimenter remained outside the rat's visual field. Note that degree of feeding neophobia could also be recast as strength of the hunger drive.

Open Field Activity. To test their open field activity levels, animals were placed in a plywood box (75 x 75 x 30 cm) and observed for 5 minutes. Outlined on the floor of the box were 25 sections (maze units) of equal size (15 x 15 cm each). The box was located in a darkened room and evenly illuminated by two overhanging 40 - Watt red light bulbs. Animals were placed in the middle of the box and their activities were recorded by an overhanging video camera. During the 5 - minute recording period, the experimenter remained out of view and monitored the animal on a TV screen. The videos were later reviewed and the total number of maze units entered was recorded for each animal. A maze unit was considered entered only if all four feet touched the surface inside the section. Prior to testing each animal, the box was wiped with a mild disinfectant solution (Deosan) to prevent odor cues from affecting the behavior of animals tested later in the session.

Runway Training. In preparation for visual discrimination testing, animals were pretrained in a straight runway (15 x 92 x 30 cm) with a 15 x 25 cm start box and a 15 x 42 cm goal box where food (.15 g of a breakfast cereal) was available at the far end in a small cup. The entire apparatus was painted grey. During the first two days of pretraining, the doors separating the start box from the remainder of the runway were in place but those separating the goal box from the runway were removed. Five seconds after being placed in the start box, the door was opened, allowing the animal to enter the runway. The animal was returned to the start box only after consuming the food available at the far end of the goal box. On the third and final day of pretraining, a grey flap door was hung at the entrance to the goal box. On all three pretraining days, animals were tested for 10 minutes. The number of times the animal entered the goal box and consumed the food (Runs) on each pretraining day were recorded.

Visual Discrimination. Visual discrimination testing was carried out with a modified Grice Maze (Grice, 1938). The goal boxes were 15 x 42 x 30 cm, the start box was 15 x 25 x 30, and the distance from the start box door to the doors of the goal boxes was 30 cm. For the black - white discrimination task, the flap door as well as the walls and floor in the middle goal box were painted white. Those of the two outer goal boxes were painted black. For the horizontal - vertical stripes discrimination task, the flap door as well as the walls and floor in the middle goal box were painted with black and white vertical 2 cm stripes. Those of the two outer goal boxes were painted with 2 cm horizontal stripes. The grey decision chamber, which allowed access to only two of the goal boxes on any given trial, and the start box comprised a movable unit that could be repositioned, allowing the counter balancing of direction and stimuli. White and vertical stripes were the positive targets for the two tasks.

Each trial began with the animal being placed into the start box. After 5 s, the door was opened giving the animal access to the decision chamber, at which time the door to the start box was closed. If the animal entered the correct goal box, it was given 30 s to feed (.15 g of the same cereal used during pretraining) and then returned to the start box for the next trial. If the animal entered the incorrect goal box, it was left there for 30 s and then returned to the start box for the next trial. If after one minute the animal failed to enter either of the goal boxes, it was returned to the start box and the trial restarted.

Each day there were 10 trials of testing, with the correct door on the left for five trials and on the right for the other five trials. The Gellerman (1933) alternation schedule was used to minimize the development of directional habits. Animals were tested on each discrimination task for 12 days or until they performed correctly on nine of ten trials on two consecutive days. On the first day of testing for each of the two discrimination tasks, animals were given two practice trials where only the correct goal box door would open. On the first practice trial, the correct door was to the right; on the second trial, it was to the left.

RESULTS AND DISCUSSION

With respect to the offspring, all dependent measures were analyzed using a randomized - block design, with biological litter and nursing litter serving as blocking variables (litter x fostering x post - weaning rearing condition x testing occasion). Given that the outcomes of the analyses using biological litter and those using nursing litter as the blocking variables were virtually identical, only those analyses using biological litter as the blocking variable will be presented.

No problems were encountered with the cross - fostering procedure; all dams appeared to fully accept their fostered pups as their own. The acceptance of the fostered pups by the dams is further revealed in the behavioral measures summarized in Table 1. There was little difference between those pups nursed by their biological dam and the fostered pups, with the possible exception of weight, F(1,9) = 3.66, MS'Symbol not transcribed'e = 2512.22, p = .07. With respect to feeding neophobia (Intake), open field activity (Activity), Runs, and visual discrimination, there were no significant main effects for fostering or significant interactions between testing occasion and fostering, all Fs

Enriched Versus Standard Rearing Conditions

The first phase in the analysis of the effects of post - weaning rearing environment was the examination of how the offspring compared on the dependent measures: feeding neophobia, open field activity, Runs, and visual discrimination. As shown in Table 2, on both testing occasions, there were distinct differences between the enriched and the standard animals on the feeding neophobia test. The enriched animals ate more than did the standard animals. These results are consistent with Holson's (1986) suspicion that enriched rats are more willing to feed in novel surroundings than are rats reared in standard conditions. Neither differences in body weight nor differences in body weight loss were found to be responsible for the amount of food consumed. The correlations between body weight and amount of food consumed on the two testing occasions were - .12 and .02, respectively. The correlation between drop in body weight and amount of food consumed on the second testing occasion was .05.

In addition to the main effect for post - weaning condition, F(1,9) = 5.22, MS'Symbol not transcribed'e = 2.30, p

As depicted in Table 2, in terms of open field activity, there was a significant interaction between condition and occasion, F(1, 9) = 33.62, MS'Symbol not transcribed'e = 272.44, p .05). The within post - weaning condition correlations, however, were .50 (standard) (p

With respect to number of Runs, there was a main effect for occasion (Table 2), F(2,18) = 51.11, MS'Symbol not transcribed'e = 7.97, p .05, despite the enriched animals having been less active in the open field and having shown less feeding neophobia. The absence of an interaction between condition and occasion, F(1, 9) = 2.73, MS'Symbol not transcribed'e = 3.38, p > .05, again indicates that there were no differential practice effects. The mean between - occasion correlation (r = .73, p

With respect to visual discrimination, there was a significant interaction between post - weaning rearing condition and task, F(1, 9) = 10.11, MS'Symbol not transcribed'e = 1.04, p

The next phase in the analysis was to explore the relations among the four dependent measures. The first step was to create a single more reliable score for feeding neophobia (Feeding), Runs, and open field activity (Activity) by summing across occasions. In this phase, only the scores from the black - white discrimination task (Learning) were used as a measure of rate of learning. As can be seen in Table 3, on the whole, the zero - order correlations among the aggregate variables and Learning were quite small and nonsignificant, both overall and within post - weaning rearing conditions. Most importantly with respect to the primary purpose of our study, none of the other three variables was found to predict Learning. Furthermore, a multiple regression using Learning as the criterion and Feeding, Runs, and Activity as the predictors produced a nonsignificant R'Symbol not transcribed'2 of only .07.

The effect of post - weaning rearing environment on learning appears to be independent of the more general temperamental factors, at least those measured here. This would suggest that not all enriched animals are uniformly affected by - or perhaps not equally exposed to - all facets of the enriched environment. Although performance on the Hebb - Williams maze may be sensitive to an animal's willingness to feed in a novel situation and to the animal's general activity level, the present data indicate that environmental effects on learning are not simply the byproducts of these temperament factors.

Dams

Like their offspring, the dams increased their food consumption from the first occasion (M = 0.76 g, SD = .61) to the second occasion (M = 1.51 g, SD = .99) of feeding neophobia testing, F(1, 9) = 6.32, MS'Symbol not transcribed'e = .55, p .05). This contrasts with the within - condition stability found in the offspring. With respect to the open field testing, the mean activity level of the dams was virtually unchanged across the two occasions, F

As can be seen in Table 4, consistent with the offspring data, the correlations among the three aggregate variables and Learning were weak and nonsignificant. Most importantly, none of the other three predictor variables was found to be significantly related to performance on the black - white discrimination task. Furthermore, as in the case of the offspring, a multiple regression using Learning as the criterion and Feeding, Runs, and Activity as the predictors produced a nonsignificant R'Symbol not transcribed'2 of only .18, F

Finally, to explore the possible effects of biological and nursing dam, we correlated the performances of the dams with the performances of their biological pups that they nursed, with the performances of their biological pups that were fostered out, and with the performances of the pups that they fostered and nursed. Contrary to what might have been anticipated on the basis of the breeding studies reviewed in the introduction, we found little evidence of genetic or other direct biological effects on the four dependent measures. An examination of Table 5 reveals no trace of the positive manifold that would be expected across the first four columns if the dams influenced the behavior of their biological offspring, nor is there a hint of the positive manifold that would be expected across the two right hand columns if the dams affected the behavior of the pups that they nursed.

There are at least two conceivable explanations for these negative results. First, even though the Long - Evans rats used in our study were from an outbred strain, the relevant genes may all have been monomorphic. Second, the proportion of error variance associated with the behavioral measures may have been too great, given the number of animals included in this study. It must be said, however, that the power of our study was sufficient to reveal the substantial impact of the post - weaning rearing environments.

In summary, the performance of animals nursed by a fostering dam did not differ from that of animals nursed by their biological dam. As suspected by Holson (1986), the animals reared in the enriched conditions ate more food in a novel situation than did the animals reared in standard conditions. Consistent with previous research on learning rates, rats reared in enriched post - weaning environments out - performed, at least initially, their counterparts reared in standard post - weaning conditions. Although post - weaning rearing condition produced differences in feeding neophobia, open field activity, runway training, and learning, these effects appear to be relatively independent of each other.

Our findings do not give solace to anyone expecting to find a single temperament factor, and we found no evidenced that the effects of enrichment on learning are simply the byproduct of effects on temperament factors. Additionally, the effect of post - weaning condition on learning does not appear to be irreversible. The relative improvement of the standard animals on the second discrimination task - albeit with the benefit of additional practice - demonstrates the continuing impact of differential experience. With respect to future research, it would be worthwhile to see if increased practice on one type of learning task reduces the learning deficit that would be expected in standard animals on a dissimilar type of learning task. With respect to the heritability of the behavioral measures we examined, we found no evidence of a genetic component. We explored two sources of malleability: nursing dam and post - weaning rearing environment. Although the latter was found to be of consequence, the former was not. In conclusion, the substantial effects post - weaning environments have on various behaviors seem to be independent, but not irreversible.

This research was supported by the Division of Life Sciences, University of Toronto, Scarborough Campus. We thank John Bassili, Janelle LeBoutillier, Paul Murphy, and Liz Head for their assistance. Correspondence should be addressed to Douglas A. Bors, Division of Life Sciences, University of Toronto at Scarborough, Scarborough, Ontario, M1C 1A4 (e - mail: bors@lake.scar.utoronto.ca).

References

Bors, D.A. (1994). Is the nature - nurture debate on the verge of extinction? Canadian Psychology, 35, 231 - 243.

Cooper, R. & Zubek, J. (1958). Effects of enriched and restricted early environments on the learning ability of bright and dull rats. Canadian Journal of Psychology, 12, 159 - 164.

Diamond, M.C. (1988). Enriching heredity: The impact of the environment on the anatomy of the brain. New York: The Free Press.

Gellerman, L.W. (1933). Chance orders of alternating stimuli in visual discrimination experiments. Journal of Genetic Psychology, 42, 207 - 208.

Greenough, W.T., Yuwiler, A., & Dollinger, M. (1973). Effects of posttrial eserine administration on learning in "enriched" - and "impoverished" - reared rats. Behavioral Biology, 8, 261 - 272.

Grice, G.R. (1938). The relation of secondary reinforcement to delayed reward in visual discrimination learning. Journal of Experimental Psychology, 38, 1 - 16.

Hatch, A.M., Balazs, T., Wiberg, G.S., & Grice, H.C. (1963). Long - term isolation stress in rats. Science, 142, 507 - 508.

Hebb, D.O. (1947). The effects of early experience on problem - solving ability at maturity. American Psychology, 2, 306 - 307.

Holson, R.R. (1986). Feeding neophobia: A possible explanation for the differential maze performance of rats reared in enriched or isolated environments. Physiology & Behavior, 38, 191 - 201.

Holson, R.R., Scallet, A.C., Ali, S.F., & Turner, B.B. (1991). "Isolation stress" revisited: Isolation - rearing effects depend on animal care methods. Physiology & Behavior, 49, 1107 - 1118.

Janus, K. (1987). Effects of early separation of young rats from the mother on their open - field behavior. Physiology & Behavior, 40, 711 - 715.

Luchins, A.A., & Forgus, R.H. (1955). The effect of differential post - weaning environments on the rigidity of an animal's behavior. Journal of Genetic Psychology, 86, 51 - 58.

Meier, G.W., & McGee, R.K. (1959). A re - evaluation of the effect of early perceptual experience on discrimination performance during adulthood. Journal of Comparative and Physiological Psychology, 52, 390 - 395.

Morton, N.E. (1974). Analysis of family resemblance. I. Introduction. American Journal of Human Genetics, 26, 318 - 330.

Myers, R.D., & Fox, J. (1963). Differences in maze performance of group - vs. isolation - reared rats. Psychological Reports, 12, 199 - 202.

Rosenzweig, M.R., & Bennett, E.L. (1976). Enriched environments: Facts, factors, and fantasies. In J.L. McGaugh & L. Petrinovich (Eds.), Knowing, thinking, and believing (pp. 179 - 213). New York: Plenum Press.

Scarr, S. (1981). Genetics and the development of intelligence. In S. Scarr (Ed.), Race, social class and individual differences in IQ (pp. 61 - 74). Hillsdale, NJ: Erlbaum.

Searle, L.V. (1949). The organization of hereditary maze brightness and maze dullness. Genetic Psychology Monographs, 39, 279 - 325.

Sirevaag, A.M., & Greenough, W.T. (1988). A multivariate statistical summary of synaptic plasticity measures in rats exposed to complex, social and individual environments. Brain Research, 441, 386 - 392.

Thompson, W.R. (1954). The inheritance and development of intelligence. Proceedings of the Association for Research in Nervous and Mental Diseases, 33, 209 - 231.

Tryon, R.C. (1940). Genetic differences in maze learning in rats. In National Society for the Study of Education, The thirty - ninth yearbook. Bloomington, IL: Public School Publishing.

Zimbardo, P.G., & Montgomery, K.C. (1957). Effects of "free - environment" rearing upon exploratory behavior. Psychological Reports, 3, 589 - 594.

Footnotes:

(f.1) It may be helpful if we begin by making explicit our position on the nature - nurture debate, along with our interpretive framework. Although degree of heritability has regularly been the focus of the nature - nurture debate, we believe that the question of malleability has always been at its core (see Bors, 1994). We also concur with those who maintain that heritability and malleability are independent of each other (Bors, 1994; Morton, 1974; Scarr, 1981). In a given sample or population, the extent to which the range, mean, and standard deviation of a particular behavior or trait can be influenced is independent of the proportion of the variance associated with genotype. Given these as our assumptions, we have no intention of drawing conclusions concerning the relative ontological weights of genes and environment in determining behavior. We simply hope to identify effects and their possible interrelations.

TABLE 1

Descriptive Statistics: Non - Fostered and Fostered Offspring

Non - Fostered Offspring Fostered Offspring

Measure M SD M SD

Weight 1 350.00 30.00 326.00 33.00

Weight 2 323.00 26.00 305.00 29.00

Intake 1 0.61 0.69 0.91 0.94

Intake 2 3.02 1.35 3.58 1.59

Activity 1 102.02 26.78 101.64 16.79

Activity 2 117.84 28.40 118.62 31.94

Runs 1 6.00 3.45 6.00 2.47

Runs 2 10.59 5.11 10.24 3.99

Runs 3 12.11 5.27 12.62 3.07

Black/White 4.74 1.49 4.71 1.45

Stripes 3.84 1.02 3.67 2.15

Note. Weight 1 and Weight 2 are in grams. Intake 1 and Intake 2 are grams consumed during feeding neophobia testing. Activity 1 and Activity 2 are the number of maze units entered in the open field. Runs 1, 2, and 3 are the number of times the animals traversed the length of the straight runway during the pretraining for the discrimination task. Black/White and Stripes are the days to criterion on the two discrimination tasks.

TABLE 2

Descriptive Statistics: Standard and Enriched Offspring

Standard Offspring Enriched Offspring

Measure M SD M SD

Weight 1 341.00 37.00 334.16 29.00

Weight 2 318.00 33.00 309.00 23.00

Intake 1 0.41 0.40 1.16 1.01

Intake 2 2.72 1.29 3.97 1.44

Activity 1 97.86 25.58 104.21 16.82

Activity 2 132.33 32.29 102.10 17.80

Runs 1 4.81 2.11 7.32 3.19

Runs 2 9.76 3.16 11.11 5.65

Runs 3 11.09 3.79 13.78 4.29

Black/White 5.24 1.14 4.11 1.47

Stripes 3.59 0.98 3.84 2.24

Note. Weight 1 and Weight 2 are in grams. Intake 1 and Intake 2 are grams consumed during feeding neophobia testing. Activity 1 and Activity 2 are the number of maze units entered in theopen field. Runs 1, 2, and 3 are the number of times the animals traversed the length of the straight runway during the pretraining for the discrimination task. Black/White and Stripes are the days to criterion on the two discrimination tasks.

TABLE 3

Offspring Performance: Correlations Among the Dependent Variables.

Learning Intake Activity

Intake - .22

Activity .12 - .01

Runway .03 .13 - .12

Standard Condition Offspring Only

Intake - .13

Activity .07 .38

Runway - .23 - .25 .23

Enriched Condition Offspring Only

Intake .01

Activity - .04 - .13

Runway .37 .08 - .36

Note. Learning is the days to criterion on the Black/White discrimination task. Intake is grams consumed during feeding neophobia testing. Activity is the number of maze units entered in the open field. Runway is the number of times the animals traversed the length of the straight runway during the pretraining for the discrimination task.

TABLE 4

Dam Performance: Correlations Among the Dependent Variables

Learning Intake Activity

Intake .15

Activity - .31 - .25

Runway .25 .27 .36

Note. Learning is the days to criterion on the Black/White discrimination task. Intake is grams consumed during feeding neophobia testing. Activity is the number of maze units entered in the open field. Runway is the number of times the animals traversed the length of the straight runway during the pretraining for the discrimination task.

TABLE 5

Correlations Between Dams and Their Biological and Fostered Pups

Biological Pups Biological Pups Fostered Pups

Nursed Fostered Out Nursed

Standard Enriched Standard Enriched Standard Enriched

Learning - .37 .22 - .46 .01 - .27 .03

Intake .44 .46 .01 - .61 - .21 .40

Activity - .21 - .31 - .06 .52 - .05 .05

Runs - .28 - .36 - .30 .16 - .31 .57

Note. Learning is the days to criterion on the Black/White discrimination task. Intake is grams consumed during feeding neophobia testing. Activity is the number of maze units entered in the open field. Runs is the number of times the animals traversed the length of the straight runway during the pretraining for the discrimination task. Standard and Enriched refer to the pups reared in the standard post - weaning environment and those reared in the enriched

Copyright Canadian Psychological Association Jun 1996
Provided by ProQuest Information and Learning Company. All rights Reserved