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Effects of social groupings upon emotional behaviour
EFFECTS OF SOCIAL GROUPINGS UPON EMOTIONAL BEHAVIOUR BY
VICTOR H . DENENBERG, JOHN R . C . MORTONt Purdue University.
Rats which receive handling or shock experience in infancy are significantly less emotional in adulthood than controls which are not disturbed during the infantile period (Denenberg & Smith, 1963 ; Hunt & Otis, 1963 ; Levin, 1957, 1958 ; Lindholm, 1962). Denenberg & Morton (1962) conducted two studies to determine whether suitable forms of "therapy" could be found which would overcome the effects of lack of extrinsic stimulation in infancy . In one study they found that rats which had received the same treatment in infancy and were then reared in free-environment boxes after weaning (N= 16 per box), were significantly less emotional than equivalent groups reared in standard laboratory cages . However, when handled and non-handled controls were placed into the same free environment (N=8 handled and 8 controls per box) so that they could interact with each other, subsequent open-field testing revealed that the mean difference between these two groups was significantly greater than the mean differences obtained between equivalent groups which were also reared in free environments but which could not interact with one another . In other words, social interactons between handled and non-handled animals served to accentuate differences in emotionality . In that study the ratio of handled to non-handled animals was 1 :1 . In all likelihood, this was not the optimal ratio to use if it was desired to try to reduce the emotional upset of non-handled controls . For example, on the human level Jersild (1954) has suggested that placing one emotionally upset child in with a group of well adjusted children would benefit the disturbed child . The purpose of the first experiment reported here was to vary systematically the ratio of handled and non-handled Ss which lived together in free environments to determine whether the various social groupings would differentially affect S's emotionality . That experiment only partially duplicated the results
AND
GARY C . HALTMEYER
of Denenberg & Morton (1962, Experiment 2) . Therefore a second experiment was carried out in an attempt to replicate the original Denenberg & Morton findings . Method Experiment 1 Infantile experience. The procedures followed were the same as described by Denenberg & Morton (1962) . Briefly, Purdue-Wistar rats were born in 9 inches x 9 inches x 15 inches wire mesh cages containing an external food hopper and water bottle . Litters were randomly reduced to 8 pups at birth, and complete litters were randomly assigned to the control or handling condition . Control Ss were never disturbed until weaning. Starting the day after birth, the handled Ss were removed from the cage, leaving the mother in the cage, placed for 3 minutes in a 1-gallon can containing shavings, and then returned to their home cage . This was repeated once a day through Day 24 . On Day 25 all Ss were weaned, weighed, sexed, and earpunched . Free-environment experience . The four freeenvironment boxes have been described previously (Denenberg & Morton, 1962) . They were 4 feet square and contained a number of playthings . At weaning 16 Ss were randomly selected from the litters available and placed into the free-environment boxes in the following ratios of handled (H) and control (C) Ss : 16H :OC ;12H :4C ;8H :8C ;4H :12C ;and 0 H : 16 C . The animals remained in the free environments continually until 50 days of age when they were removed and placed with likesexed litter-mates in standard laboratory cages . They remained undisturbed until 70 days of age when they were given 4 days of open-field testing, During the course of the experiment 11 Ss died . Open field testing. The open field consisted of a 45-inch square plywood base with walls 18 inches high . The complete unit was painted flat black except for thin white lines which divided the floor into 9-inch squares . The field was approximately evenly lighted throughout by overhead fluorescent lights . Previously (Denenberg & Morton, 1962) S had been introduced into the open field via a 1-gallon can which was attached to the side of the unit . In this study
*This research was supported, in part, by grants from the National Science Foundation and from the Purdue Research Foundation . tPresent address : Department of Psychology, Western Illinois University, Macomb, Illinois . 205
206
ANIMAL BEHAVIOUR, XII,
the can and entrance hole were eliminated and S was placed directly into one of the corner squares and observed for 3 minutes . The total number of squares entered and number of boluses were recorded . Experiment 2 The Denenberg & Morton studies and the experiment described above were carried out in the same laboratory with the same experimenter testing the Ss . Experiment 2 was carried out in a newer laboratory with a different experimenter . The maternity cages were of stainless steel and measured 7 inches x 10 inches x 15 inches . They also had an external food hopper and water bottle . The Ss were sexed at birth and litters were reduced to 4 males and 4 females . Four litters were handled daily as described above while 4 others were not disturbed . At 24 days Ss were weaned and placed into the same freeenvironment boxes as described above in the following ratios : 16 H :0 C ; 8 H :8 C ; and 0 H 16 C . At 50 days Ss were placed in laboratory cages where they remained undisturbed until open-field testing started at 76 days of age . The same field was used as in Experiment 1 . Ss were tested for 6 consecutive days . One female died during the course of the experiment . Results Experiment 1 The activity and defaecation means for all groups are summarized in Table I . Analysis of variance of the activity data found that Ss handled in infancy were more active than nonhandled controls (F=21 . 79, df=1/197, p< •0 1) and that females were more active than males (F=37 . 50, df=1/197, p< •0 1) . There were no significant differences among the various ratios of social groupings nor did these ratios interact with either the handling or sex variable . To see whether the social interaction between handled and non-handled S modified open-field behaviour, the activity of the groups which were "mixed" together (i .e . the 12 :4, 8 :8, and 4 :12 groups) was compared to the activity of the unmixed groups . The mixed groups had lower activity scores than the two 16 . 0 groups and the difference approached significance (F=3 . 52, df=1/197, p<-10) . The only significant differences on the bolus measure was the sex variable (F=20 . 38, df= 1/197, p< •0 1).
2 -3
Experiment 2 These data are summarized in Table 11 . The means and error variances are not directly comparable since Ss were tested for 4 days in Experiment 1 and 6 days in the second experiment . Analysis of the activity scores showed that Ss handled in infancy were more active than controls (F=25 .01, df=1/55, p< •0 1), females were more active than males (F=12 . 35, df=1/55, p< . 01), and that the handled and non-handled Ss which were mixed together in the free environments were more active than the nonmixed groups (F=5 . 39, df=1/55, p< •0 5) . None of the interactions was significant . On the bolus measure Ss mixed together in the free environment defaecated less than the nonmixed groups (F=15 . 73, df=1/55, p< . 01) . The sex difference approached significance at the •1 0 level (F=3 . 06) . Discussion The purpose of the first experiment was to investigate the effects of varying the ratio of unemotional (handled) and emotional (nonhandled) Ss in the complex free environment . It was expected that changing the ratio would act to change the social interactions and, thus, the emotionality of the handled and unhandled Ss . No evidence supporting this hypothesis was found . In the original Denenberg & Morton study (1962, Experiment 2) post-weaning social interactions in the free environment between Ss which had been handled or not disturbed in infancy resulted in an increase in the open-field activity of handled Ss and a decrease in the activity of controls . In the first experiment reported here social interactions between handled and control Ss resulted in a decrease in activity for both groups ; in the second experiment essentially the same procedures resulted in an increase in activity for both groups which were mixed together in the free environment . If no significant differences had been obtained in the current experiments, it would be reasonable to attribute the original Denenberg & Morton finding to sampling error . However, a significant effect was obtained in Experiment 2 in the current series, and the difference approached significance in Experiment 1 . Even though the differences were in opposite directions, these findings, coupled with those reported by Denenberg & Morton, do not appear consonant with a sampling error hypothesis. It is quite unlikely that the elimination of the
DENENBERG et al. : EFFECTS OF SOCIAL GROUPINGS UPON EMOTIONAL BEHAVIOUR
207
Table I . Open Field Performance in Experiment I Classified by Infantile Stimulation, Free Environment Groupings and Sex . Ratio of
Sex
Handled Ss
H :C 16 :0
12 :4
8 :8
4 :12
N Male
16
Squares
Boluses
155 . 62
12 . 06
N
Squares
Boluses
(-
Female
16
245 . 50
7 . 50
Total
32
401 . 12
19 . 56
Male
26
160 . 54
12 . 08
9
83 . 11
8 . 78
Female
21
222 . 57
9 . 33
6
163 . 83
6 . 68
Total
47
383 . 11
21 . 41
15
246 .94
15 .46
Male
7
141 . 14
11 . 86
7
135 . 43
9 . 14
Female
8
226 . 38
3 . 89
7
151 . 14
2 . 86
Total
15
367 . 52
15 . 75
14
286 . 57
12 .00
Male
7
140 . 29
12 . 86
22
71 . 36
8 . 50
Female
8
199 . 62
4 . 13
21
134 . 57
5 . 86
15
339 . 91
16 .99
43
205 . 93
14 . 36
Male
16
94 . 25
12 . 31
Female
16
216 . 81
8 . 00
Total
32
311 . 06
20 . 31
Total 0 :16
Non-handled Ss
I i
Error MS (sq uares) ~ 6301 6 8 Error MS (bo uses) =
53-59
Table II . Open Field Performance in Experiment 2 Classified by Infantile Stimulation, Free Environment Groupings and Sex . Ratio of
Sex
I
H :C 16 :0
8 :8
Handled Ss N
Squares
Boluses
Male
8
260 . 12
22 . 25
Female
8
385 . 62
16 . 63
Total
16
645 . 74
38 . 88
Male
8
311 . 50
10 . 88
Female
8
491 . 38
16
802 . 88
i Total 0 :16
Non-handled Ss N
Squares
Boluses
8
169 .75
12 . 00
11 . 00
8
285 . 75
4 . 75
21 . 88
16
455 . 50
16 . 75
Male
8
102 . 63
21 . 25
Female
7
180 . 29
17 . 00
15
282 . 92
38 . 25
Total Error MS (sq,uares) 19810 . 47 Error MS (boluses) = 92 •, 64
208
ANIMAL BEHAVIOUR, XII, 2- 3
entrance can as the method of introducing S into the open field had any significant influence, since emotionality differences have been shown under conditions as widely divergent as openfield boxes (Denenberg & Morton, 1962, 1964 ; Denenberg & Smith, 1963), drinking behaviour following 18 to 24 hours of water deprivation (Levine, 1957, 1958 ; Lindholm, 1962), and timidity tests in which S has to leave its cage and go into a strange alleyway (Hunt & Otis, 1963) . A more reasonable conclusion appears to be that one or more unknown variables are influencing the behaviour of the animals in the free environment in such a manner that their subsequent open-field behaviour is affected . Systematic observations were not taken of the play behaviour of the Ss in the free environment . Such observations may yield useful hypothesis concerning the factors involved . Social interaction between males and females does not appear to be a critical factor here. Recently Denenberg & Morton (1964) reared males and females separately in free-environment boxes or else mixed the sexes . Subsequently, open-field behaviour yielded no evidence that the presence or absence of social interaction between the sexes affected emotionality . These Ss were also compared with equivalent groups which had been reared in laboratory cages from weaning onward . The free-environment reared Ss were found to be significantly less emotional, thus confirming the original Denenberg & Morton finding (1962, Experiment 1) . Summary In Experiment 1 (N=213) rat pups were handled (H) in infancy or were non-disturbed controls (C) . At weaning Ss were placed into free-environment boxes in the following ratios (N=16 per box) : 16 H :0 C, 12 H :4 C, 8 H :8 C, 4 11 :12 C, 0 H :16 C . Ss were placed into standard laboratory cages at 50 days and given the
open-field emotionality test from 70-73 days of age . In Experiment 2 (N=63) handled and control Ss were reared in the free environment between weaning and 50 days in one of the following groupings : 16 H :0 C, 8 H :8 C ; or 0 H :16 C . Open-field testing was carried out from 76-81 days of age . In Experiment 1 Ss which were mixed together in the free environment (i .e . the 12 :4, 8 :8, and 4 :12 groupings) were less active than Ss not grouped together (p < .10) . There were no significant differences among the different social ratios. In Experiment 2 Ss mixed together were more active than the unmixed groups (p<-05) . Neither set of data is consistent with the original findings of Denenberg & Morton (1962, Experiment 2) . In both experiments handled Ss were more active than controls (p < •0 1) . REFERENCES Denenberg, V . H ., & Morton, J . R . C. (1962) . Effects of environmental complexity and social groupings upon modification of emotional behavior . J. comp. physiol. Psychol., 55, 242-246. Denenberg, V . H . & Morton, J . R . C . (1964). Infantile stimulation, prepubertal sexual-social interaction, and emotionality. Anim . Behav ., 12, 11-13 . Denenberg, V . H . & Smith, S . A . (1963) . Effects of infantile stimulation and age upon behavior . J. comp . physiol . Psychol., 56, 307-312. Hunt, H . F . & Otis, L . S . (1963) . Early "experience" and its effects on later behavioral processes in rats : I . Initial experiments . Trans . N. Y. Acad. Sci., 25, 858-870. Jersild, A . T . (1954) . Child psychology. New York : Prentice-Hall . Levine, S . (1957) . Infantile experience and consummatory behavior in adulthood . J. comp . physiol. Psychol., 50, 609-612 . Levine, S . (1958) . Noxious stimulation in infant and adult rats and consummatory behavior . J . comp, physiol. Psychol., 51, 230-233 . Lindholm, B . W . (1962) . Critical periods and the effects of early shock on later emotional behavior in the white rat . J. comp . physiol. Psychol., 55, 597-599 . (Accepted for publication 14th March, 1964 ; Ms. number : 423) .
VICTOR H . DENENBERG, JOHN R . C . MORTONt Purdue University.
Rats which receive handling or shock experience in infancy are significantly less emotional in adulthood than controls which are not disturbed during the infantile period (Denenberg & Smith, 1963 ; Hunt & Otis, 1963 ; Levin, 1957, 1958 ; Lindholm, 1962). Denenberg & Morton (1962) conducted two studies to determine whether suitable forms of "therapy" could be found which would overcome the effects of lack of extrinsic stimulation in infancy . In one study they found that rats which had received the same treatment in infancy and were then reared in free-environment boxes after weaning (N= 16 per box), were significantly less emotional than equivalent groups reared in standard laboratory cages . However, when handled and non-handled controls were placed into the same free environment (N=8 handled and 8 controls per box) so that they could interact with each other, subsequent open-field testing revealed that the mean difference between these two groups was significantly greater than the mean differences obtained between equivalent groups which were also reared in free environments but which could not interact with one another . In other words, social interactons between handled and non-handled animals served to accentuate differences in emotionality . In that study the ratio of handled to non-handled animals was 1 :1 . In all likelihood, this was not the optimal ratio to use if it was desired to try to reduce the emotional upset of non-handled controls . For example, on the human level Jersild (1954) has suggested that placing one emotionally upset child in with a group of well adjusted children would benefit the disturbed child . The purpose of the first experiment reported here was to vary systematically the ratio of handled and non-handled Ss which lived together in free environments to determine whether the various social groupings would differentially affect S's emotionality . That experiment only partially duplicated the results
AND
GARY C . HALTMEYER
of Denenberg & Morton (1962, Experiment 2) . Therefore a second experiment was carried out in an attempt to replicate the original Denenberg & Morton findings . Method Experiment 1 Infantile experience. The procedures followed were the same as described by Denenberg & Morton (1962) . Briefly, Purdue-Wistar rats were born in 9 inches x 9 inches x 15 inches wire mesh cages containing an external food hopper and water bottle . Litters were randomly reduced to 8 pups at birth, and complete litters were randomly assigned to the control or handling condition . Control Ss were never disturbed until weaning. Starting the day after birth, the handled Ss were removed from the cage, leaving the mother in the cage, placed for 3 minutes in a 1-gallon can containing shavings, and then returned to their home cage . This was repeated once a day through Day 24 . On Day 25 all Ss were weaned, weighed, sexed, and earpunched . Free-environment experience . The four freeenvironment boxes have been described previously (Denenberg & Morton, 1962) . They were 4 feet square and contained a number of playthings . At weaning 16 Ss were randomly selected from the litters available and placed into the free-environment boxes in the following ratios of handled (H) and control (C) Ss : 16H :OC ;12H :4C ;8H :8C ;4H :12C ;and 0 H : 16 C . The animals remained in the free environments continually until 50 days of age when they were removed and placed with likesexed litter-mates in standard laboratory cages . They remained undisturbed until 70 days of age when they were given 4 days of open-field testing, During the course of the experiment 11 Ss died . Open field testing. The open field consisted of a 45-inch square plywood base with walls 18 inches high . The complete unit was painted flat black except for thin white lines which divided the floor into 9-inch squares . The field was approximately evenly lighted throughout by overhead fluorescent lights . Previously (Denenberg & Morton, 1962) S had been introduced into the open field via a 1-gallon can which was attached to the side of the unit . In this study
*This research was supported, in part, by grants from the National Science Foundation and from the Purdue Research Foundation . tPresent address : Department of Psychology, Western Illinois University, Macomb, Illinois . 205
206
ANIMAL BEHAVIOUR, XII,
the can and entrance hole were eliminated and S was placed directly into one of the corner squares and observed for 3 minutes . The total number of squares entered and number of boluses were recorded . Experiment 2 The Denenberg & Morton studies and the experiment described above were carried out in the same laboratory with the same experimenter testing the Ss . Experiment 2 was carried out in a newer laboratory with a different experimenter . The maternity cages were of stainless steel and measured 7 inches x 10 inches x 15 inches . They also had an external food hopper and water bottle . The Ss were sexed at birth and litters were reduced to 4 males and 4 females . Four litters were handled daily as described above while 4 others were not disturbed . At 24 days Ss were weaned and placed into the same freeenvironment boxes as described above in the following ratios : 16 H :0 C ; 8 H :8 C ; and 0 H 16 C . At 50 days Ss were placed in laboratory cages where they remained undisturbed until open-field testing started at 76 days of age . The same field was used as in Experiment 1 . Ss were tested for 6 consecutive days . One female died during the course of the experiment . Results Experiment 1 The activity and defaecation means for all groups are summarized in Table I . Analysis of variance of the activity data found that Ss handled in infancy were more active than nonhandled controls (F=21 . 79, df=1/197, p< •0 1) and that females were more active than males (F=37 . 50, df=1/197, p< •0 1) . There were no significant differences among the various ratios of social groupings nor did these ratios interact with either the handling or sex variable . To see whether the social interaction between handled and non-handled S modified open-field behaviour, the activity of the groups which were "mixed" together (i .e . the 12 :4, 8 :8, and 4 :12 groups) was compared to the activity of the unmixed groups . The mixed groups had lower activity scores than the two 16 . 0 groups and the difference approached significance (F=3 . 52, df=1/197, p<-10) . The only significant differences on the bolus measure was the sex variable (F=20 . 38, df= 1/197, p< •0 1).
2 -3
Experiment 2 These data are summarized in Table 11 . The means and error variances are not directly comparable since Ss were tested for 4 days in Experiment 1 and 6 days in the second experiment . Analysis of the activity scores showed that Ss handled in infancy were more active than controls (F=25 .01, df=1/55, p< •0 1), females were more active than males (F=12 . 35, df=1/55, p< . 01), and that the handled and non-handled Ss which were mixed together in the free environments were more active than the nonmixed groups (F=5 . 39, df=1/55, p< •0 5) . None of the interactions was significant . On the bolus measure Ss mixed together in the free environment defaecated less than the nonmixed groups (F=15 . 73, df=1/55, p< . 01) . The sex difference approached significance at the •1 0 level (F=3 . 06) . Discussion The purpose of the first experiment was to investigate the effects of varying the ratio of unemotional (handled) and emotional (nonhandled) Ss in the complex free environment . It was expected that changing the ratio would act to change the social interactions and, thus, the emotionality of the handled and unhandled Ss . No evidence supporting this hypothesis was found . In the original Denenberg & Morton study (1962, Experiment 2) post-weaning social interactions in the free environment between Ss which had been handled or not disturbed in infancy resulted in an increase in the open-field activity of handled Ss and a decrease in the activity of controls . In the first experiment reported here social interactions between handled and control Ss resulted in a decrease in activity for both groups ; in the second experiment essentially the same procedures resulted in an increase in activity for both groups which were mixed together in the free environment . If no significant differences had been obtained in the current experiments, it would be reasonable to attribute the original Denenberg & Morton finding to sampling error . However, a significant effect was obtained in Experiment 2 in the current series, and the difference approached significance in Experiment 1 . Even though the differences were in opposite directions, these findings, coupled with those reported by Denenberg & Morton, do not appear consonant with a sampling error hypothesis. It is quite unlikely that the elimination of the
DENENBERG et al. : EFFECTS OF SOCIAL GROUPINGS UPON EMOTIONAL BEHAVIOUR
207
Table I . Open Field Performance in Experiment I Classified by Infantile Stimulation, Free Environment Groupings and Sex . Ratio of
Sex
Handled Ss
H :C 16 :0
12 :4
8 :8
4 :12
N Male
16
Squares
Boluses
155 . 62
12 . 06
N
Squares
Boluses
(-
Female
16
245 . 50
7 . 50
Total
32
401 . 12
19 . 56
Male
26
160 . 54
12 . 08
9
83 . 11
8 . 78
Female
21
222 . 57
9 . 33
6
163 . 83
6 . 68
Total
47
383 . 11
21 . 41
15
246 .94
15 .46
Male
7
141 . 14
11 . 86
7
135 . 43
9 . 14
Female
8
226 . 38
3 . 89
7
151 . 14
2 . 86
Total
15
367 . 52
15 . 75
14
286 . 57
12 .00
Male
7
140 . 29
12 . 86
22
71 . 36
8 . 50
Female
8
199 . 62
4 . 13
21
134 . 57
5 . 86
15
339 . 91
16 .99
43
205 . 93
14 . 36
Male
16
94 . 25
12 . 31
Female
16
216 . 81
8 . 00
Total
32
311 . 06
20 . 31
Total 0 :16
Non-handled Ss
I i
Error MS (sq uares) ~ 6301 6 8 Error MS (bo uses) =
53-59
Table II . Open Field Performance in Experiment 2 Classified by Infantile Stimulation, Free Environment Groupings and Sex . Ratio of
Sex
I
H :C 16 :0
8 :8
Handled Ss N
Squares
Boluses
Male
8
260 . 12
22 . 25
Female
8
385 . 62
16 . 63
Total
16
645 . 74
38 . 88
Male
8
311 . 50
10 . 88
Female
8
491 . 38
16
802 . 88
i Total 0 :16
Non-handled Ss N
Squares
Boluses
8
169 .75
12 . 00
11 . 00
8
285 . 75
4 . 75
21 . 88
16
455 . 50
16 . 75
Male
8
102 . 63
21 . 25
Female
7
180 . 29
17 . 00
15
282 . 92
38 . 25
Total Error MS (sq,uares) 19810 . 47 Error MS (boluses) = 92 •, 64
208
ANIMAL BEHAVIOUR, XII, 2- 3
entrance can as the method of introducing S into the open field had any significant influence, since emotionality differences have been shown under conditions as widely divergent as openfield boxes (Denenberg & Morton, 1962, 1964 ; Denenberg & Smith, 1963), drinking behaviour following 18 to 24 hours of water deprivation (Levine, 1957, 1958 ; Lindholm, 1962), and timidity tests in which S has to leave its cage and go into a strange alleyway (Hunt & Otis, 1963) . A more reasonable conclusion appears to be that one or more unknown variables are influencing the behaviour of the animals in the free environment in such a manner that their subsequent open-field behaviour is affected . Systematic observations were not taken of the play behaviour of the Ss in the free environment . Such observations may yield useful hypothesis concerning the factors involved . Social interaction between males and females does not appear to be a critical factor here. Recently Denenberg & Morton (1964) reared males and females separately in free-environment boxes or else mixed the sexes . Subsequently, open-field behaviour yielded no evidence that the presence or absence of social interaction between the sexes affected emotionality . These Ss were also compared with equivalent groups which had been reared in laboratory cages from weaning onward . The free-environment reared Ss were found to be significantly less emotional, thus confirming the original Denenberg & Morton finding (1962, Experiment 1) . Summary In Experiment 1 (N=213) rat pups were handled (H) in infancy or were non-disturbed controls (C) . At weaning Ss were placed into free-environment boxes in the following ratios (N=16 per box) : 16 H :0 C, 12 H :4 C, 8 H :8 C, 4 11 :12 C, 0 H :16 C . Ss were placed into standard laboratory cages at 50 days and given the
open-field emotionality test from 70-73 days of age . In Experiment 2 (N=63) handled and control Ss were reared in the free environment between weaning and 50 days in one of the following groupings : 16 H :0 C, 8 H :8 C ; or 0 H :16 C . Open-field testing was carried out from 76-81 days of age . In Experiment 1 Ss which were mixed together in the free environment (i .e . the 12 :4, 8 :8, and 4 :12 groupings) were less active than Ss not grouped together (p < .10) . There were no significant differences among the different social ratios. In Experiment 2 Ss mixed together were more active than the unmixed groups (p<-05) . Neither set of data is consistent with the original findings of Denenberg & Morton (1962, Experiment 2) . In both experiments handled Ss were more active than controls (p < •0 1) . REFERENCES Denenberg, V . H ., & Morton, J . R . C. (1962) . Effects of environmental complexity and social groupings upon modification of emotional behavior . J. comp. physiol. Psychol., 55, 242-246. Denenberg, V . H . & Morton, J . R . C . (1964). Infantile stimulation, prepubertal sexual-social interaction, and emotionality. Anim . Behav ., 12, 11-13 . Denenberg, V . H . & Smith, S . A . (1963) . Effects of infantile stimulation and age upon behavior . J. comp . physiol . Psychol., 56, 307-312. Hunt, H . F . & Otis, L . S . (1963) . Early "experience" and its effects on later behavioral processes in rats : I . Initial experiments . Trans . N. Y. Acad. Sci., 25, 858-870. Jersild, A . T . (1954) . Child psychology. New York : Prentice-Hall . Levine, S . (1957) . Infantile experience and consummatory behavior in adulthood . J. comp . physiol. Psychol., 50, 609-612 . Levine, S . (1958) . Noxious stimulation in infant and adult rats and consummatory behavior . J . comp, physiol. Psychol., 51, 230-233 . Lindholm, B . W . (1962) . Critical periods and the effects of early shock on later emotional behavior in the white rat . J. comp . physiol. Psychol., 55, 597-599 . (Accepted for publication 14th March, 1964 ; Ms. number : 423) .