Based on Rijt-Plooij and Plooij's (1992) research on emergence of regression periods in the first two years of life, the presence of such periods in a group of 18 babies (10 boys and 8 girls, aged between 3 weeks and 14 months) from a Catalonian population was analyzed. The measurements were a questionnaire filled in by the infants' mothers, a semi-structured weekly tape-recorded interview, and observations in their homes. The procedure and the instruments used in the project follow those proposed by Rijt-Plooij and Plooij. Our results confirm the existence of the regression periods in the first year of children's life. Inter-coder agreement for trained coders was 78.2% and within-coder agreement was 90.1 %. In the discussion, the possible meaning and relevance of regression periods in order to understand development from a psychobiological and social framework is commented upon.

According to the literature about developmental changes, periods of instability and disorganization in the social and emotional behavior in both human and non-human primate, infancy precedes major developmental achievements or transitions (Heimann, 2003; Sparrow & Brazelton, 2006). Developmental investigators have observed a more frequent and prolonged crying, clinging and bids for physical contact with mother during these periods of instability and disorganization. Some authors, according to Horwich (1974), called these periods regression periods. Rijt-Plooij and Plooij (1992) claimed that 10 regression periods could be identified during the first 20 months of human life. In an early study, Sadurní and Rostan (2002) confirmed the presence of 8 such regression periods during the first year of life of 18 Catalan babies. Their 8 regression periods were comparable to the first 8 of the 10 regression periods found by Van de Rijt Plooij and Plooij. The aim of the present study is to see whether the regression periods that we found are temporally related to some transition. We define a transition as the occurrence of a new developmental change in a child. In the present study we have used non-analyzed data from the same 18 Catalan babies (10 boys and 8 girls) as mentioned in our earlier published study on regression periods. The age of these babies was between 3 weeks and 14 months. Using a microgenetic methodology we have found 8 transitions periods in the first year of life. We have also observed a temporal relation between the regressions periods found earlier and the transition periods reported here.