Effects of response-contingency and stimulus presentation schedule on imprinting in the chick (Gallus gallus domesticus).

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The effects of operant control over the presentation of a conspicuous imprinting stimulus on the formation of a filial preference were examined in day-old domestic chicks. Experimental chicks had to press one of two operant pedals to be exposed to the training object, a rotating red box. Chicks in a yoked control group received the same pattern of exposure to the object, but exposure was not contingent upon the chicks' response. In a second control group, the chicks were exposed to the object according to a fixed-interval schedule. The chicks' preferences were measured 2 hr after the end of training in a simultaneous choice test involving the red box and a novel stimulus. There was no significant difference in preference between the experimental chicks and their yoked controls. The mean preference of both groups was significantly higher than that of the fixed-interval control group, a result suggesting that a variable schedule of exposure to the training object enhances the formation of a preference. This was confirmed in a further experiment in which a variable interval/variable duration schedule of exposure to the object led to a significantly higher preference than a fixed-interval/fixed-duration exposure schedule. The results do not support the hypothesis that response contingency affects the formation of filial preferences. A variable schedule of exposure to an imprinting object accelerates the formation of a preference for that object, relative to a fixed schedule.