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ALLAN H. SCHULMAN. Virginia Polytechnic Institute and State ... studied extensively in humans (Davidson, Suppes, &. Siegel, 1957; Edwards, 1954, 1960).
Transitivity of social choice: Developmental considerations ALLAN H. SCHULMAN Virginia Polytechnic Institute and State University Blacksburg, Va. 24061

preferences are termed PAD and PDC , Prediction 1 states that not only will the choice behavior show strong stochastic transitivity, but that

Eighty-two female rats, ranging in age from 15 to 120 days, were each given a spatial preference test among the three possible pairings of the following three stimuli: an The purpose of the present study was (1) to identify agemate, a model of an agemate, and her own mirror image. An examination of the proportion of choices developmental trends in social choice behavior in the rat, directed toward each alternative revealed that (1) as age and (2) to determine whether the Dawkins threshold increases, so does the preference for an agemate, and (2) all age groups demonstrated a serial ordering of model is applicable to such social choice behavior. stimulus preferences with a rather good fit to Prediction 1 METHOD derived from Dawkins's (1969a, b) threshold model of Subjects choice behavior.

Observers long have been impressed with the extreme specificity associated with the development of social preferences. This is especially true within the context of imprinting research, where the nature of early experience is viewed as the prepotent factor in determining the object of social choice of precocial neonates (Lorenz, 1935; Hess, 19S9;Sluckin, 1965; Schulman & Anderson, 1972). Choice behavior in other than social contexts has been studied extensively in humans (Davidson, Suppes, & Siegel, 1957; Edwards, 1954, 1960). Central to most of these statistical theories of decision making are the interacting concepts of "subjective utility," which refers to the S's evaluation of the attractiveness of the choice alternatives, and "subjective probability," which refers to the S's estimation of the likely consequences of the alternative courses of action. In a series of experiments, Logan (1965a,b) has empirically approximated the animal equivalents of these two factors by manipulating reward magnitude and reward delay in a double alley with a good fit to human decision making theory. Dawkins's (1969a, b) work provides a different approach to animal choice behavior. Rather than emphasizing the role of anticipated outcome in determining choice, as do most of the theories of human decision making, Dawkins's probabalistic threshold model views the interaction of a randomly fluctuating internal excitatory variable with stimulus alternatives of differing thresholds as being the primary determinant for switching between the alternatives. In essence, the Dawkins model attempts to explain choice behavior in terms of moment-to-moment shifts in a threshold equivalent of subjective utility. Although McFarland (1971) recently has questioned the ability of the threshold model to "explain" decisions, the model does generate what Dawkins terms Prediction 1. Specifically, if three stimuli (A, B, and C) are presented in all three possible pairings, and if the percentage preference, that is, the proportion of responses received by the most preferred when paired with the least preferred is termed PAC while the other two percentage Bull. Psychon. Soc., 1973, Vol. 1 (6A)

The Ss were 82 female hooded rats (Rattus Norvegicus) from the colony maintained by the Psychology Department at Virginia Polytechnic Institute and State University. They comprised four age groups: 15 days (N = 18),20 days (N = 24),50 days (N = 20), and 120 days (N = 20). All Ss, except those in the two youngest age groups, were socially reared in unisexual groups from weaning until the time of testing.

Apparatus The testing apparatus was similar to that used by Schuhnan & Anderson (1972). It consisted of a wooden box, which measured 80 x 30 x 30 cm and had a hardware cloth floor. The box was divided into three compartments: a large central compartment, measuring 60 x 30 x 30 cm, and two adjacent smaller compartments, each measuring 10 x 30 x 30 cm. The partitions separating the compartments were either transparent or mirrored glass. A platform, 28 x 7.5 x 0.3 em, was located on the floor ofthe large compartment equidistant between the glass partitions. Procedure Each S was given a lO-trial choice test for each of the three possible pairings of the follOWing social stimuli: an agemate, a model of an agemate, or her own reflection in a mirror. This was accomplished by placing the S on the platform in the central compartment and determining which of the adjacent compartments, containing one of the stimulus alternatives, was approached. Stimulus position was varied systematically for each S, and the order of the paired presentations was balanced within age groups. The number of choices directed to each alternative permitted the determination of the preferred order of stimuli for each age group as well as the percentage preferences for each pairing, i.e., the proportion of responses directed toward the preferred alternative of each pair.

RESULTS AND DISCUSSION Barnett (1963) defines social behavior as being limited to interactions among members of the same species. In the present experiment, various approximations of a normal social stimulus, i.e., a conspecific, were presented to rats of various ages in order to determine their choice behavior among them. Table 1 summarizes, for each age group, the stimulus ordering, the percentage preference for each stimulus pair, and the predicted percentage preference of the most preferred stimulus when paired with the least preferred as derived from Dawkins's (1969a, b) Prediction 1. The IS-day-old Ss, tested 1 day after their eyes had opened, preferred their own reflections over an inanimate model or a live agemate. The 20-day-old Ss, 425

Table 1 Choice Behavior of Rats of Four Different Ages Age (Days) 15

20

Percent Preference (X ± SD) Preferred Order A Mirror Image B Model C Agemate A Model B Agemate C Mirror Image

PAB

PBC

PAC

Predicted PAC·

54.4 ± 5.85

71.7 ± 7.52

55.6 ± 5.96

74.2

55.0 ± 5.94

55.0 ± 5.82

62.1 ± 6.58

59.4

50

A Agemate B Mirror Image C Model

51.1 ± 5.24

54.2 ± 5.61

53.7:t 5.52

55.2

120

A Agemate B Mirror Image C Model

54.5:t 5.70

61.5 :t 5.70

64.0:t 6.58

64.9

·Derived from Dawkins' Prediction 1 (1969a, b)

about to be weaned, preferred the model over the other stimuli; the mirror image was the least preferred stimulus within this age group. By the time rats are 50 days of age, however, they demonstrate a clear preference for an agemate rather than their own reflections or a model of a rat. These data suggest that a spatial preference for a biologically appropriate social stimulus, i.e., another rat, increases with age in the domestic rat. Although the choice behavior of the two younger groups of Ss differed from that of the older Ss tested, the responses of all age groups were asymmetrical, transitive, and connected (Stevens, 1951), thereby providing evidence for a serial ordering of the test stimuli that is present in Ss even as young as 15 days. Because the choice data are not independent, ordinary statistical analyses are precluded; however, a comparison of the observed PAC and the predicted PAC for each age group reveals that Dawkins's Prediction 1 is quite accurate, especially for rats older than 15 days. These data suggest that the Dawkins model, originally applied to choices among simple stimulus alternatives, may be extended to situations involving complex social stimuli as well. Moreover, the strength of the Dawkins model in the present situation is further demonstrated by its ability to predict with a high degree of precision, even when percentage preferences are modest (Le., close to 50.0).

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REFERENCES

Barnett. S. A. The rat: A study In behaviour. Chicago: Aldine. 1972. Davidson. D .• Suppes. P., &. Siegel. S. Decision 1IUJking: An experimental approach. Stanford: Stanford University Press, 1907. Dawkins, R. A threshold model of choice behaviour. Animal Behaviour. 1969a.17, 120-133. Dawkins, R . The attention threshold model. Animal Behaviour. 1969b.17.134-141. Edwards. W. The theory of decision making. Psychological Bulletin. 1904.01.380-417. Edwards. W. Measurement of utility and subjective probability. In H. Gulliksen and S. Messick (Eds.).Paychological scaling. New York: Wiley. 1960. Pp. 109-127 . Hess. E. H . lmprinting. Science. 1959. 130. 133-141. Logan. F. A . Decision making by rats: Delay versus amount of reward. Journal of Comparative &. Physiological Psychology, 1960a, 59,1-12 Logan. F. A. Decision making by rats: Uncertain outcome choices. Journal of Comparative &. Physiological Psychology, 1965b. 59. 246-251. Lorenz. K. Der Kumpan in der Umwelt des Vogels. Journal of Ornithology. 1935 . 83.137-213,289-413. McFarland, D . J. Feedback mechanisms in animal behaviour. New York: Academic Press, 1971. Schulman, A. H ., &. Anderson, J . N. The effect of early rearing conditions upon the preferences for mirror-image stimulation in domestic chicks. Paper presented at ihe Southeastern Psychological Association meeting, Atlanta, Georgia, 1972. Sluckin, W. Imprinting and early learning. Chicago: Aldine, 1965. Stevens, S. S. Mathematics, measurement, and psychophysics. In S. S. Stevens (Ed .), Handbook of experimental psychology . New York: Wiley, 1951.Pp. 1-49.

(Received for publication March 22, 1973.)

Bull. Psychon, Soc., 1973, Vol. 1 (6A)