caretaker effect in rats

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Developmental Psychology 1969, Vol. 1, No. 6, 771 CARETAKER EFFECT IN RATS 1 ROBERT B. McCALL 2 Pels Research Institute, Yellow Springs, Ohio MICHAEL L. LESTER ANDCARL M. CORTER University of North Carolina at Chapel Hill A previous study suggested that enriched rats might spend more time on the side of an open field that was overseen by their caretaker than by a stranger (McCall, Lester, & Dolan, 1969). A follow-up study was performed in which two experimenters each reared 20 ani- mals in order to test the caretaker effect di- rectly. The enriched rearing conditions and testing apparatus were the same as in the McCall et al. study. Forty females (following the previous study) were divided by the split-litter tech- nique into two groups at weaning (24 days) and each group was "reared" by a separate caretaker. The animals were housed on opposite sides of the same cage rack in a restricted area of a small room. Except for the fact that the caretakers handled each of their animals for 20 seconds once per week and carried out all maintenance, the two groups were reared under nearly iden- tical circumstances. Testing began at 103 days of age and the apparatus and procedure were identical to McCall et al.'s, except that each caretaker handled his animals for 3 seconds prior to testing. Five minutes of free explora- tion was permited each subject on 4 consecu- tive days. Caretaker side and other parameters of the test situation were counterbalanced. 1 This research was supported by a National Institute of Health Biomedical support grant awarded to the University of North Carolina, grants from the Faculty Research Council of the University of North Carolina, and by Na- tional Institute of Health Research Grant 05537 awarded to the Fels Research Institute. An extended report of this study may be ob- tained without charge from Robert B. McCall, Department of Psychology, Fels Research In- stitute, Yellow Springs, Ohio 45387, or for a fee from the National Auxiliary Publications Service. Order Document No. 00595 from National Auxiliary Publications Service of the American Society for Information Science, c/o CCM Information Sciences, Inc., 909 Third Ave- nue, New York, New York 10022. Remit in advance $1.00 for microfiche or $3.00 for photocopies and make checks payable to: Re- search and Microfilm Publications, Inc. 2 Requests for reprints should be sent to Robert B. McCall at the address given in Footnote 1. The subjects spent an average of 99 seconds on the side of the field adjacent to their care- taker versus 75 seconds on the other side (p < .001). There was no interaction with particu- lar caretakers, and 17 of 20 subjects in each group displayed this tendency to spend more time near their caretaker. Special tops were then fitted to the field in order to test whether this effect was mediated by visual or olfactory cues. For the olfactory condition, a piece of Plexiglas overlaid with thin tissue paper was elevated above the verti- cal sides of the field leaving an "air space," but it extended 2 inches beyond the sides ("eaves"). Thus, the subjects could not see out but extrafield odors could be detected. In the visual condition, the tissue paper was re- moved permitting the subjects to see out, but the top was solidly joined to the sides so that outside olfactory stimuli were not available. Within each caretaker's group, the subjects were divided into the visual and olfactory groups so that the degree of caretaker prefer- ence (Days 1-4) was approximately equal. Four days of testing followed Days 1-4 with- out interruption. The position of the caretaker was reversed so that each subject had to re- locate him. When olfactory but not visual cues were available, the subjects spent more time in the field at large than under the visual condition (p < .01). Further, the caretaker effect emerged if olfactory cues were present (75 versus 61 seconds) but not if only visual stimuli were available (55 versus 53, p < .01). The previous study plus these data show that animals spend more time on the side of their caretaker than on the side of a stranger; and the "preference" is mediated by olfactory as opposed to visual cues. Interestingly, in each case the effect showed no acquisition phase but was full-blown on Day 1. REFERENCE MCCALL, R. B., LESTER, M. L., & DOLAN, C. G. Differential rearing and the exploration of stimuli in the open field. Developmental Psy- chology, 1969, 1, 750-762. (Received June 12, 1969) 771

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Page 1: Caretaker effect in rats

Developmental Psychology1969, Vol. 1, No. 6, 771

CARETAKER EFFECT IN RATS1

ROBERT B. McCALL2

Pels Research Institute, Yellow Springs, OhioMICHAEL L. LESTER AND CARL M. CORTER

University of North Carolina at Chapel Hill

A previous study suggested that enriched ratsmight spend more time on the side of an openfield that was overseen by their caretaker thanby a stranger (McCall, Lester, & Dolan,1969). A follow-up study was performed inwhich two experimenters each reared 20 ani-mals in order to test the caretaker effect di-rectly.

The enriched rearing conditions and testingapparatus were the same as in the McCall et al.study. Forty females (following the previousstudy) were divided by the split-litter tech-nique into two groups at weaning (24 days) andeach group was "reared" by a separate caretaker.The animals were housed on opposite sides ofthe same cage rack in a restricted area of a smallroom. Except for the fact that the caretakershandled each of their animals for 20 secondsonce per week and carried out all maintenance,the two groups were reared under nearly iden-tical circumstances. Testing began at 103 daysof age and the apparatus and procedure wereidentical to McCall et al.'s, except that eachcaretaker handled his animals for 3 secondsprior to testing. Five minutes of free explora-tion was permited each subject on 4 consecu-tive days. Caretaker side and other parametersof the test situation were counterbalanced.

1 This research was supported by a NationalInstitute of Health Biomedical support grantawarded to the University of North Carolina,grants from the Faculty Research Council ofthe University of North Carolina, and by Na-tional Institute of Health Research Grant 05537awarded to the Fels Research Institute.

An extended report of this study may be ob-tained without charge from Robert B. McCall,Department of Psychology, Fels Research In-stitute, Yellow Springs, Ohio 45387, or for afee from the National Auxiliary PublicationsService. Order Document No. 00595 fromNational Auxiliary Publications Service of theAmerican Society for Information Science, c/oCCM Information Sciences, Inc., 909 Third Ave-nue, New York, New York 10022. Remitin advance $1.00 for microfiche or $3.00 forphotocopies and make checks payable to: Re-search and Microfilm Publications, Inc.

2 Requests for reprints should be sent to RobertB. McCall at the address given in Footnote 1.

The subjects spent an average of 99 secondson the side of the field adjacent to their care-taker versus 75 seconds on the other side (p <.001). There was no interaction with particu-lar caretakers, and 17 of 20 subjects in eachgroup displayed this tendency to spend moretime near their caretaker.

Special tops were then fitted to the field inorder to test whether this effect was mediatedby visual or olfactory cues. For the olfactorycondition, a piece of Plexiglas overlaid withthin tissue paper was elevated above the verti-cal sides of the field leaving an "air space,"but it extended 2 inches beyond the sides("eaves"). Thus, the subjects could not seeout but extrafield odors could be detected. Inthe visual condition, the tissue paper was re-moved permitting the subjects to see out, butthe top was solidly joined to the sides so thatoutside olfactory stimuli were not available.

Within each caretaker's group, the subjectswere divided into the visual and olfactorygroups so that the degree of caretaker prefer-ence (Days 1-4) was approximately equal.Four days of testing followed Days 1-4 with-out interruption. The position of the caretakerwas reversed so that each subject had to re-locate him.

When olfactory but not visual cues wereavailable, the subjects spent more time in thefield at large than under the visual condition(p < .01). Further, the caretaker effectemerged if olfactory cues were present (75versus 61 seconds) but not if only visual stimuliwere available (55 versus 53, p < .01).

The previous study plus these data show thatanimals spend more time on the side of theircaretaker than on the side of a stranger; andthe "preference" is mediated by olfactory asopposed to visual cues. Interestingly, in eachcase the effect showed no acquisition phase butwas full-blown on Day 1.

REFERENCE

MCCALL, R. B., LESTER, M. L., & DOLAN, C.G. Differential rearing and the exploration ofstimuli in the open field. Developmental Psy-chology, 1969, 1, 750-762.

(Received June 12, 1969)

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