Combined predisposed preferences for colour and biological motion make robust development of social attachment through imprinting
To study how predisposed preferences shape the formation of social attachment through imprinting, newly hatched domestic chicks (Gallus gallus domesticus) were simultaneously exposed to two animations composed of comparable light points in different colours (red and yellow), one for a walking motion and another for a linear motion. When a walking animation in red was combined with a linear one in yellow, chicks formed a learned preference for the former that represented biological motion (BM). When the motion–colour association was swapped, chicks failed to form a preference for a walking in yellow, indicating a bias to a specific association of motion and colour. Accordingly, experiments using realistic walking chicken videos revealed a preference for a red video over a yellow one, when the whole body or the head was coloured. On the other hand, when the BM preference had been pre-induced using an artefact moving rigidly (non-BM), a clear preference for a yellow walking animation emerged after training by the swapped association. Even if the first-seen moving object was a nonbiological artefact such as the toy, the visual experience would induce a predisposed BM preference, making chicks selectively memorize the object with natural features. Imprinting causes a rapid inflow of thyroid hormone in the telencephalon leading to the induction of the BM preference, which would make the robust formation of social attachment selectively to the BM-associated object such as the mother hen.
KeywordsEarly social deprivation Sensitive period Thyroid hormone Developmental homeostasis Conspec–Conlern mechanism Domestic chicks
We thank Dr. Giorgio Vallortigara (University of Trento, Italy) for his critical comments and discussions on our manuscript. We also thank the editor and anonymous referees for instructive suggestions. Contribution of Mr. Yasutaka Sasaki (Machine Department of the Faculty of Science, Hokkaido University) must be acknowledged for production of the imprinting apparatus.
TM and MM conceived the study and designed the experiments. MM developed the animations, designed the experimental procedures, analysed the data, and prepared the figures. MM and DN carried out the experiments. T.M. developed the apparatus and the computer programmes. TM and MM wrote the manuscript and supplementary materials. All the authors gave final approval for publication.
The present study was supported by grants funded to TM by the Japan Society for Promotion of Science (JSPS, Kakenhi; Grants-in-aid for Scientific Research #25291071, #26650114, #18K07351).
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