Occurrence of Regressive Periods in the Normal Development of Swedish Infants
Previous findings indicate the existence of several regression periods linked to developmental transitions within the infancy period (e.g., from birth to 15 months), but no consensus exists concerning how many periods are to be expected (Bever, 1982; Fischer, 1987; van de Rijt-Plooij & Plooij, 1992). The standard psychologicalliterature usually reports only three periods centered around the ages of 2,7, and 12 months (Plooij & van de Rijt-Plooij, 1989; Fischer, 1987), whereas in contrast, van de Rijt-Plooij and Plooij (1992) found evidence for nine regression periods during the infancy period (at 4-5,7-9,11-12,14-19,22-26,32-37,40--46,49-52, and 61-64 weeks of age). These results, based on detailed observations of both free living chimpanzees and human infants, cast serious doubt on the current understanding of early infant development. Thus, these findings need to be replicated and extended in order to substantiate the existence of such regression periods and to specify their frequency and timing. The purpose of the present
study is, therefore, to observe a graup of Swedish infants in order to investigate whether a pattern of regressions similar to that reported by van de Rijt-Plooij and Plooij (1992) can be detected.