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Many child development experts are skeptical and say that it contradicts their training and the variability in the timing of skills acquisition. Others find it accurate and helpful.<ref>{{Cite news |last=Wapner |first=Jessica |date=2020-04-16 |title=Are Sleep Regressions Real? |language=en-US |work=The New York Times |url=https://www.nytimes.com/2020/04/15/parenting/baby/sleep-regression.html |url-status=live |access-date=2023-12-17 |archive-url=https://web.archive.org/web/20230605155926/https://www.nytimes.com/2020/04/15/parenting/baby/sleep-regression.html |archive-date=2023-06-05 |issn=0362-4331 |quote=In other words, timed leaps may be real, but the evidence hasn’t proven if or in what capacity they exist. Neurologists are just beginning to understand brain patterns during the first two years of life. “We really are at the infancy of infant brain knowledge,” said Dr. Hirsh-Pasek, the psychologist at Temple University. Some pediatricians, though, believe Dr. Plooij’s theory is correct. Dr. Pamela Hops, M.D., a pediatrician in New York City, said that during her 20 years of practice, she has anecdotally seen and heard about changes in babies that perfectly align with the 10 leaps Dr. Plooij described. “I think he’s spot on,” said Dr. Hops, “shockingly so.” }}</ref> [[T._Berry_Brazelton|Brazelton]] found it to be mutually confirmatory with his own work.<ref name=Sparrow2013>{{cite journal |last1=Sparrow |first1=J. |date=2013 |title=Newborn Behavior, Parent–Infant Interaction, and Developmental Change Processes: Research Roots of Developmental, Relational, and Systems-Theory-Based Practice |url= |journal=Journal of Child and Adolescent Psychiatric Nursing |volume=26 |issue=3 |pages=180–185 |doi=10.1111/jcap.12047 |pmid=23909940 |access-date=}}</ref><ref name=Plooij-2010>{{Citation | last1 = Plooij | first1 = F. X. | author-link = | chapter = The 4 WHY’s of age-linked regression periods in infancy | editor-last1 = Lester | editor-first1 = B. M. | editor-last2 = Sparrow | editor-first2 = J. D. | title = Nurturing Children and Families: Building on the Legacy of T. Berry Brazelton | pages = 107–119 | volume = | publisher = Wiley-Blackwell | place=Malden, MA | publication-date = 2010 | isbn = }}</ref> |
Many child development experts are skeptical and say that it contradicts their training and the variability in the timing of skills acquisition. Others find it accurate and helpful.<ref>{{Cite news |last=Wapner |first=Jessica |date=2020-04-16 |title=Are Sleep Regressions Real? |language=en-US |work=The New York Times |url=https://www.nytimes.com/2020/04/15/parenting/baby/sleep-regression.html |url-status=live |access-date=2023-12-17 |archive-url=https://web.archive.org/web/20230605155926/https://www.nytimes.com/2020/04/15/parenting/baby/sleep-regression.html |archive-date=2023-06-05 |issn=0362-4331 |quote=In other words, timed leaps may be real, but the evidence hasn’t proven if or in what capacity they exist. Neurologists are just beginning to understand brain patterns during the first two years of life. “We really are at the infancy of infant brain knowledge,” said Dr. Hirsh-Pasek, the psychologist at Temple University. Some pediatricians, though, believe Dr. Plooij’s theory is correct. Dr. Pamela Hops, M.D., a pediatrician in New York City, said that during her 20 years of practice, she has anecdotally seen and heard about changes in babies that perfectly align with the 10 leaps Dr. Plooij described. “I think he’s spot on,” said Dr. Hops, “shockingly so.” }}</ref> [[T._Berry_Brazelton|Brazelton]] found it to be mutually confirmatory with his own work.<ref name=Sparrow2013>{{cite journal |last1=Sparrow |first1=J. |date=2013 |title=Newborn Behavior, Parent–Infant Interaction, and Developmental Change Processes: Research Roots of Developmental, Relational, and Systems-Theory-Based Practice |url= |journal=Journal of Child and Adolescent Psychiatric Nursing |volume=26 |issue=3 |pages=180–185 |doi=10.1111/jcap.12047 |pmid=23909940 |access-date=}}</ref><ref name=Plooij-2010>{{Citation | last1 = Plooij | first1 = F. X. | author-link = | chapter = The 4 WHY’s of age-linked regression periods in infancy | editor-last1 = Lester | editor-first1 = B. M. | editor-last2 = Sparrow | editor-first2 = J. D. | title = Nurturing Children and Families: Building on the Legacy of T. Berry Brazelton | pages = 107–119 | volume = | publisher = Wiley-Blackwell | place=Malden, MA | publication-date = 2010 | isbn = }}</ref> |
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==Scientific Basis== |
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Ethologists have documented predictable regression periods in the interactions of mothers and infants in many species, suggesting an early origin in evolution of species.<ref name="Horwich74">{{cite journal |last1=Horwich |first1=Robert H. |date=1974 |title="Regressive Periods in Primate Behavioral Development with Reference to Other Mammals" |url= https://www.researchgate.net/publication/226450864 |journal=Primates |volume=15 |issue=2–3 |pages=141–149 |doi= 10.1007/BF01742277|s2cid=6922407 |access-date=2024-02-26}}</ref><ref>{{cite book |date=1983 |editor-last=Hinde |editor-first=R.A. |title=Primate Social Relationships: An Integrated Approach |publisher=Blackwell Scientific |location=Oxford |pages= |chapter= |isbn=}}</ref><ref>"Before our research, such regression phases had been found by others in 12 other primate species and two lower mammalian species, indicating that this appears to be an old phenomenon, perhaps emerging during the very evolution of life on earth" ("Introduction" (by F.X. Plooij), ''ibid.'' p. 15).</ref> In the course of a longitudinal (1971-1973) ethological study of chimpanzees in the wild, working with Jane Goodall,<ref>{{cite news |last=Rojas-Rocha |first=Xochitl |date=2014-08-22 |title=Gombe chimpanzee calls available after 40-year wait |url=https://www.science.org/content/article/gombe-chimpanzee-calls-available-after-40-year-wait |url-status= |language= |issue=22579 |publisher=American Association for the Advancement of Science |work=Science News |location= |archive-url= |archive-date= |access-date=2024-02-25 |via= |quote=}}</ref> van de Rijt and Plooij published additional data demonstrating predictable regression periods in Chimpanzee mother-infant dyads.<ref>{{cite journal |last=Plooij |first=F.X. |editor-last=Lipsitt |editor-first=L.P. |date=1984 |title=The Behavioral Development of Free-living Chimpanzee Babies and Infants |url= |journal=Monographs on Infancy |volume=3 |issue= |pages=1–207 |publisher=Ablex Publishing |publication-place=New York |doi= |s2cid= |access-date= }}</ref><ref>{{cite journal |last1=van de Rijt-Plooij |first1=H.H.C. |last2=Plooij |first2=F. X. |date=1987 |title=Growing independence, conflict and learning in mother-infant relations in free-ranging chimpanzees |url= |journal=Behaviour |volume=101 |issue=1-3 |pages=1–86 |doi=10.1163/156853987X00378 |s2cid= |access-date= }}</ref><ref>{{cite journal |last1=van de Rijt-Plooij |first1=H.H.C. |last2=Plooij |first2=F. X. |date=1988 |title=Mother-infant relations, conflict, stress and illness among free-ranging chimpanzees |url= |journal=Developmental Medicine & Child Neurology |volume=30 |issue=3 |pages=306-15 |doi= |s2cid= |pmid=3402672 |access-date= }}</ref> They saw in this a new type of learning important in the evolution of human parenting, with reference to an explanation in control theory.<ref name=canalization>{{cite journal |last1=Plooij |first1=F. X. |last2=van de Rijt-Plooij |first2=H.H.C. |date=1989 |title=Evolution of human parenting: Canalization, new types of learning, and mother-infant conflict |url= |journal=European Journal of Psychology of Education |volume=4 |issue= |pages=177–192 |doi=10.1007/BF03172599 |s2cid= |pmid= |access-date= }}</ref> They then applied the observational methods of ethology to humans. Their first human study, involving 15 Dutch mothers and their infants, with extrinsic sources of stress carefully controlled, was published in the ''Journal of Reproductive and Infant Psychology'' in 1992.<ref name="Plooijs1992">{{Cite journal |last1=Van De Rijt-Plooij |first1=Hedwig H.C. |last2=Plooij |first2=Frans X. |date=July 1992 |title=Infantile regressions: Disorganization and the onset of transition periods |journal=Journal of Reproductive and Infant Psychology |language=en |volume=10 |issue=3 |pages=129–149 |doi=10.1080/02646839208403946 |issn=0264-6838}}</ref> |
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<!-- In the same year a book for the general public was published in the [[Dutch language]].<ref>{{Cite book |last1=Van De Rijt |first1=Hetty |last2=Plooij |first2=Frans X. |date=1992 |title=Oei, ik groei! |trans-title=Ai, I'm growing! |language=nl |location=Ede and Antwerp |publisher=Zomer & Keuning Boeken BV }}</ref> --> |
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These behavioral observations have been correlated with stages of neurological development of the brain.<ref name="Plooij-ABS">{{cite journal | last1 =Plooij | first1 =F. X. | last2 = Rijt-Plooij | first2 = H. H. C. van de | title = Developmental transitions as successive reorganizations of a control hierarchy | journal = American Behavioral Scientist | volume = 34 | issue = 1 | pages =67–80 | date = 1990 | language = English | url = | jstor = | issn = | doi = 10.1177/0002764290034001007 | s2cid =144183592 }}</ref> Research into development of the central nervous system has shown that the periods of rapid change (PRC) begin at the same times as the observed regression periods,<ref name="Trevarthen-Aitken03">{{Cite book |last1=Trevarthen|first1=C. |last2=Aitken|first2=K. |url=https://www.google.com/books/edition/Regression_Periods_in_Human_Infancy/mSZ5AgAAQBAJ?hl=en&gbpv=1&dq=regression+periods+in+human+infancy&printsec=frontcover |title=Regression periods in human infancy |date=2003 |publisher=Erlbaum |isbn=0-8058-4098-2 |editor-last=Heimann |editor-first=Mikael |place=Mahwah, NJ |pages=107-184 |chapter=Regulation of Brain Development and Age-Related Changes in Infants’ Motives: The Developmental Function of Regressive Periods}}</ref> and parents' informal observations that babies master a cluster of new skills after each regression period has been verified.<ref>{{cite book | last1 = Sadurni | first1 = M. | last2 = Burriel | first2 = M. P. | last3 = Plooij | first3 = F. X. | author-link = | date = 2010 | title = The temporal relation between regression and transition periods in early infancy | url = | journal = The Spanish Journal of Psychology | volume = 13 | issue = 1 | pages = 112-126 | doi = | access-date = }}</ref> There is an uptick of illness during a regression period. |
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==Controversy== |
==Controversy== |
Revision as of 03:18, 6 July 2024
The Wonder Weeks: A Stress-Free Guide to Your Baby's Behavior is a book with advice to parents about child development by physical anthropologist Hetty van de Rijt and ethologist and developmental psychologist Frans Plooij. Xaviera Plas-Plooij is a third author of recent editions. It was first published in English in 2003[1] as the translation of the 1992 Dutch book Oei, ik groei![2] The 6th edition in 2019[3] includes a chapter on sleep.[4] The book claims that the cognitive development of babies occurs in predictably timed stages.[4] This has long been a controversy in developmental psychology.[5] Experts in child development have objected that sleep regressions are not so predictable.[6] The publisher has produced a mobile app based on the book.[7]
Claims
The book describes 10 predictable 'leaps' observed in a child's cognitive development during the first 20 months, with 8 in the first year. Months are counted from the due date because development begins with conception.[8] This is a period of tremendous growth in the brain. The brain reaches half its adult size within the first three months after birth.[9] Brain volume is about 35% of adult volume 2–3 weeks after birth, doubles from term size in the first year of life and increases an additional 15% in the second to about 80% of adult size.[10]
The 'regression period' is the first phase of a 'leap', during which the infant's previously confident control is disrupted by having to learn to perceive and control at a new and more abstract level of the growing perceptual hierarchy. This is followed by another period in which the baby is generally happy, due to discovering new things with the newly gained cognitive skills. The 'leaps' are predicted to occur at about 5, 8, 12, 19, 26, 37, 46, 55, 64 and 75 weeks of age (from the due date), although the timing for learning particular skills associated with them varies from one child to another.[11][12]
Reception
Many child development experts are skeptical and say that it contradicts their training and the variability in the timing of skills acquisition. Others find it accurate and helpful.[13] Brazelton found it to be mutually confirmatory with his own work.[14][15]
Controversy
The question whether the early childhood development process is gradual or punctuated by distinct biologically determined advances has been controversial in developmental psychology since the beginning of the 20th century.[5][16] Obvious developmental milestones or transitions, such as grasping, crawling or walking for the first time, do not correlate with genetically scheduled developments, but a correlation has been reported for periods of infants' insecurity, called regression periods.[17] Environmental sources of stress can obscure this by cluttering the data.[17][18][19][20]
Plooij obtained state funding to oversee an independent replication. With this funding he obtained a one day a week position as a "Professor by special appointment" (Dutch: bijzonder hoogleraar) at his alma mater, the University of Groningen.[21] He engaged Carolina de Weerth, a PhD student of Paul van Geert.[22] At the conclusion of her research, she reported that she had found many periods of greater fussiness and higher cortisol levels other than at the predicted times.[23][24] Plooij said that this was because three of the four mothers that she had recruited did not meet the stated criteria for a replication because their circumstances and behavior introduced extrinsic sources of stress for the infant which made it difficult to discern distress specifically at times of new developments.[17][18][19][20]
Plooij objected to these results being published as a replication. He resigned his position, which was near its end, subsequently asked to rescind his resignation, and was refused.[25] Dutch newspapers reported that de Weert was Plooij's PhD student and had refuted his research, and that Plooij had been dismissed.[25][26] According de Weerth, Plooij tried to pressure her into not publishing the study.[25][27] Plooij disputes this account,[27] and de Weert's results were published jointly with van Geert as the lead author.[28]
The controversy was made a focal topic in the journal Neuropsychiatrica with an article by Plooij, [17]a rejoinder by van Geert and de Weert,[29] and a refutation by Plooij.[18]
The Plooijs' 1992 study has subsequently been independently replicated at universities in three countries, Oxford in England,[20] Girona in Spain,[30][31] and Gothenburg in Sweden.[32] Plooij's research has continued.[33]
References
- ^ Vanderijt, Hetty; Plooij, Frans X. (2003). The wonder weeks: how to turn your baby's 8 great fussy phases into magical leaps forward. Emmaus, Pa: Rodale. ISBN 978-1-57954-645-8.
- ^ Van De Rijt, Hetty; Plooij, Frans X. (1992). Oei, ik groei! [Ai, I'm growing!] (in Dutch). Ede and Antwerp: Zomer & Keuning Boeken BV.
- ^ Rijt, Hetty van de; Plooij, Frans X.; Plas-Plooij, Xaveira (September 2019). The Wonder Weeks: A Stress-Free Guide to Your Baby's Behavior. New York: W. W. Norton. p. 464. ISBN 978-1-68268-427-6.
- ^ a b Verhoeven, Eymeke (2018-03-07). "Je kind loopt nog niet? Maakt niet uit" [Your child isn't walking yet? It doesn't matter]. Nederlands Dagblad (in Dutch). Retrieved 2024-02-25.
- ^ a b Kalverboer, L. (1998). "Ontwikkelingssprongen in het duister: Over transities in de ontwikkeling" [Developmental leaps in the dark: On transitions in development]. Neuropraxis. 1. doi:10.1007/BF03070912.
Verloopt het vroegkinderlijke ontwikkelingsproces geleidelijk of sprongsgewijs? Deze vraag houdt onderzoekers bezig sinds het begin van deze eeuw, toen de systematische studie van de ontwikkeling van het kind begon.
[Is the early childhood development process gradual or in leaps? This question has preoccupied researchers since the beginning of this century, when the systematic study of child development began.] - ^ Wapner, Jessica (2020-04-16). "Are Sleep Regressions Real?". The New York Times. ISSN 0362-4331. Archived from the original on 2023-06-05. Retrieved 2023-12-17.
- ^ "The Wonder Weeks App". The Wonder Weeks. Retrieved 2017-08-27.
- ^ The Wonder Weeks (2017 ed.) p. 23.
- ^ Holland, D.; Chang, L.; Ernst, T.M.; et al. (2024-10-01). "Structural Growth Trajectories and Rates of Change in the First 3 Months of Infant Brain Development". JAMA Neurol. 71 (10): 1266–1274. doi:10.1001/jamaneurol.2014.1638.
- ^ Gilmore, J.H.; Knickmeyer, R.C.; Gao, W. (2018-02-16). "Imaging structural and functional brain development in early childhood". Nat. Rev. Neurosci. 19 (3): 123–137. doi:10.1038/nrn.2018.1.
- ^ Cite error: The named reference
TWW2019
was invoked but never defined (see the help page). - ^ Xaveira Plas-Plooij: {{cite web |url=https://www.mrsshilts.co.uk/interview-xaviera-plas-plooij-wonder-weeks/ |title=An interview with Xaviera Plas Plooij |last=Shilton |first=Emma |date=2014-05-15 |website=Hello Mrs. Shilts |publisher= |access-date=2024-02-26 |quote=The research stopped at 20 months as this is when we realised that by then parents are able to decipher when their children are going through leaps. As children grow older into teenagers and young adults, there [are] 3 or 4 much bigger leaps such as puberty and further on the ‘mid-life crisis’. The research would be enormous if we studied all of those so it was best to concentrate on the first 20 months when parents need help making informed choices and information on how their children are developing.}
- ^ Wapner, Jessica (2020-04-16). "Are Sleep Regressions Real?". The New York Times. ISSN 0362-4331. Archived from the original on 2023-06-05. Retrieved 2023-12-17.
In other words, timed leaps may be real, but the evidence hasn't proven if or in what capacity they exist. Neurologists are just beginning to understand brain patterns during the first two years of life. "We really are at the infancy of infant brain knowledge," said Dr. Hirsh-Pasek, the psychologist at Temple University. Some pediatricians, though, believe Dr. Plooij's theory is correct. Dr. Pamela Hops, M.D., a pediatrician in New York City, said that during her 20 years of practice, she has anecdotally seen and heard about changes in babies that perfectly align with the 10 leaps Dr. Plooij described. "I think he's spot on," said Dr. Hops, "shockingly so."
- ^ Sparrow, J. (2013). "Newborn Behavior, Parent–Infant Interaction, and Developmental Change Processes: Research Roots of Developmental, Relational, and Systems-Theory-Based Practice". Journal of Child and Adolescent Psychiatric Nursing. 26 (3): 180–185. doi:10.1111/jcap.12047. PMID 23909940.
- ^ Plooij, F. X. (2010), "The 4 WHY's of age-linked regression periods in infancy", in Lester, B. M.; Sparrow, J. D. (eds.), Nurturing Children and Families: Building on the Legacy of T. Berry Brazelton, Malden, MA: Wiley-Blackwell, pp. 107–119
- ^ Kagan, Jerome; Herschkowitz, Norbert (2014-01-01). "Preface". A Young Mind in a Growing Brain. New York: Psychology Press. p. xi.
The argument that a select set of human psychological properties cannot appear until certain maturational events have occurred bothers a number of American and European social scientists. We understand their resistance to the suggestion that there are natural restraints on the time of emergence of some human competences. Western society values freedom of action and the continual contribution of experience to biological structures.
- ^ a b c d Plooij, F. X. (1998). "Hersenveranderingen en 'sprongen' in de eerste 20 levensmaanden en de invloed van de context op gedragsmaten van regressieperioden" [Brain changes and 'leaps' in the first 20 months of life and the influence of context on behavioral measures of regression periods]. Acta Neuropsychiatrica. 10 (3): 63–66. doi:10.1017/S0924270800036590.;|quote= Het idee dat er een koppeling te leggen valt tussen rijping van het zenuwstelsel en ontwikkelings-mijlpalen of -transities, zoals voor het eerst grijpen, kruipen of lopen, is onhoudbaar gebleken. Wel valt er een koppeling in de tijd te leggen tussen hersenveranderingen en regressieperioden |trans-quote= The idea that there is a link between nervous system maturation and developmental milestones or transitions, such as grasping, crawling or walking for the first time, has proven untenable. However, a temporal link can be established between brain changes and regression periods …. Cite error: The named reference "Plooij1998a" was defined multiple times with different content (see the help page).
- ^ a b c Plooij, F. X. (1998). "Repliek op 'Empirische indicatoren voor regressies en sprongen bij baby's'" [Reply to 'Empirical indicators of regressions and leaps in infants']. Acta Neuropsychiatrica. 10 (3): 74–77. doi:10.1017/S0924270800036619.
- ^ a b Plooij, F. X.; Rijt-Plooij, H. H. C. van de (2003), "The effects of sources of "noise" on direct observation measures of regression periods: Case studies of four infants' adaptations to special parental conditions.", in Heimann, M. (ed.), Regression periods in human infancy, Mahwah, NJ: Erlbaum, pp. 57–80, ISBN 978-0805840988
- ^ a b c Woolmore, A.; Richer, J. (2003). "Detecting infant regression periods: weak signals in a noisy environment". In Heimann, M. (ed.). Regression periods in human infancy. Mahwah, NJ: Erlbaum. pp. 23–39. ISBN 978-0805840988.
- ^ Kreulen, Edwin (2024-08-18). "En-plooij, hij springt verder" [And Plooij, he jumps further]. Trouw. Retrieved 2024-02-25.
Plooij, appointed as a special professor at the University of Groningen for one day a week, hired a PhD student who should substantiate the theory.
- ^ Kok, Annemarie (1997-11-19). "'Oei, ik groei!' leidt tot bittere ruzie van wetenschappers" ['Ouch, I'm growing!' leads to bitter arguments among scientists]. Trouw (in Dutch). Retrieved 2024-02-26.
Volgens hoogleraar P. van Geert, die onderzoekster De Weerth de laatste jaren heeft begeleid, is het boek enerzijds gebaseerd op bestaande, betrouwbare ontwikkelingspsychologische kennis.
[According to Professor P. van Geert, who has guided researcher De Weerth in recent years, the book is based on existing, reliable developmental psychological knowledge.] - ^ de Weerth, C.; van Geert, P. (1998-03-01). "Emotional instability as an indicator of strictly timed infantile developmental transitions". British Journal of Developmental Psychology. 16 (1): 15–44. doi:10.1111/j.2044-835X.1998.tb00748.x. ISSN 2044-835X.
- ^ Cite error: The named reference
trouw
was invoked but never defined (see the help page). - ^ a b c Kok, Annemarie (1997-11-19). "'Oei, ik groei!' leidt tot bittere ruzie van wetenschappers" ['Ouch, I'm growing!' leads to bitter arguments among scientists]. Trouw (in Dutch). Retrieved 2024-02-26.
- ^ Dirks, Bart (1998-01-14). "Positie Plooij onhoudbaar na openlijke kritiek op oud-promovenda; Auteur 'Oei, ik groei' ontslagen als hoogleraar" [Plooij's position untenable after open criticism of former PhD candidate; Author 'Oops, I'm growing' dismissed as professor]. Volkskrant. Retrieved 14 June 2015.
- ^ a b {{Cite news |last=Wapner |first=Jessica |date=2020-04-16 |title=Are Sleep Regressions Real? |language=en-US |work=The New York Times |url=https://www.nytimes.com/2020/04/15/parenting/baby/sleep-regression.html |url-status=live |access-date=2023-12-17 |archive-url=https://web.archive.org/web/20230605155926/https://www.nytimes.com/2020/04/15/parenting/baby/sleep-regression.html |archive-date=2023-06-05 |issn=0362-4331 |quote=
- ^ Weerth, C. d., & Geert, P. v. (1998). Emotional instability as an indicator of strictly timed infantile developmental transitions. British Journal of Developmental Psychology, 16, 15-44
- ^ Geert, P. v.; Weerth, C. d. (1998). "Empirische indicatoren voor regressies en sprongen bij baby's" [Empirical indicators of regressions and leaps in infants]. Acta Neuropsychiatrica. 10 (3): 67–73. doi:10.1017/S0924270800036607.
- ^ Sadurní, M.; Rostan, C. (2002). "Regression periods in infancy: A case study from Catalonia". Spanish Journal of Psychology. 5 (1): 36–44. doi:10.1017/s1138741600005813. hdl:10256/1720. PMID 12025364.
- ^ Sadurní, M.; Rostan, C. (2003). "Reflections on regression periods in the development of Catalan infants". In Heimann, Mikael (ed.). Regression periods in human infancy. Mahwah, NJ: Erlbaum. pp. 7–22. ISBN 0-8058-4098-2.
- ^ Lindahl, L.; Heimann, M.; Ullstadius, E. (2003). "Occurrence of regressive periods in the normal development of Swedish infants". In Heimann, M. (ed.). Regression periods in human infancy. Mahwah, NJ: Erlbaum. pp. 41–55. ISBN 978-0805840988.
- ^ Plooij, F. X. (2010). "The 4 WHY's of Age-Linked Regression Periods in Infancy". In Lester, B. M.; Sparrow, J. D. (eds.). Nurturing Children and Families: Building on the Legacy of T. Berry Brazelton. Malden, MA: Wiley-Blackwell. pp. 107–119.