Passman, R. H.; Halonen, J. S. «A developmental survey of young children's attachments to inanimate objects». Journal of Genetic Psychology, 134, 2, 1979, pàg. 165–178. DOI: 10.1080/00221325.1979.10534051.
Halonen, J. S.; Passman, R. H. «Pacifiers' effects upon play and separations from the mother for the one-year-old in a novel environment». Infant Behavior and Development, 1, 1978, pàg. 70–78. DOI: 10.1016/S0163-6383(78)80010-1.