AN NOTATI’ON
The Normal Crying Curve: What Do We Really Know?
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DESCRIPTIONSof behavioural curves exert considerable influence on our way of thinking about development. In recent years there has been increasing interest in infant crying behaviour, both as a developmental phenomenon and as a clinical problem (commonly referred to as ‘colic’). Crying is usually described in terms of a behavioural curve, characterized by an early increase to a peak during the second month, a decrease until about four months, and little change thereThe pattern raises interesting but unanswered questions about biological and behavioural factors affecting crying. Following their own extensive study of the phenomenon, EMDE and colleaguesS concluded that ‘early fussiness is puzzling and does seem to be unexplained’ (p. 84). Despite (or perhaps because of) the lack of explanation, the curve is usually interpreted as describing the normal pattern of crying. As such, it provides a potential basis for understanding infant development and for approaching clinical complaints’s 6. The word ‘normal’ is fraught with ambiguity, especially in the clinical context’. As an adjective, it implies (1)’ that the noun it modifies refers to an entity that is in some sense natural, appropriate, or optimal, perhaps even necessary and unchangeable; and (2) that 2 9 5 9
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a distinction can be made between that which is normal and abnormal. These connotations represent potentially important claims, but not ones which will be discussed here (see BARR~). In the present context, ‘normal’ refers only t o that which is described as the crying of normal (non-pathological) infants. The usefulness of the ‘normal crying curve’ depends on the accuracy and completeness with which it describes crying behaviour, for it constrains the possible interpretations of the origin and meaning of early crying. Despite considerable consensus about its main characteristics, important questions remain about what process (or processes) the ‘normal curve’ describes. Stimulated by the technique of cry spectrographjl, interest has focused on microlevel descriptions of cry morphology and the importance of specific cry features for listener response or diagnostic prediction (for a review, see LESTERand BOUKYDIS’).By and large, however, developmental changes have involved more macrolevel descriptions of duration and frequency over hours, days, weeks or months, based primarily on diaries, with occasional support from short-term direct observations and audiorecordings. From these studies, there are five propositions about which most observers agree: first, there is a progressive increase in crying which peaks in the second month and then gradually decreases; second, there is a diurnal rhythm, typified by clustering during the evening hours, most marked during peak crying in the second month; third, there is considerable between-individual variability, again most
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Fig. I . A (above) and B (below). Patterns of cry (and/or fuss) behaviour over first three months (A) or first two years (B)of life. Data derived from referenced publications are plotted as percentage of total reported crying for tho1 study. Consequently, patterns. but not amounts of crying, are comparable across studies. (A) Closed diamonds, Bloom and McDo welt'; closed squares, Rebelsky and Black'; open diamonds, Hunziker and Barr (control group)'; open squares, Brazelton open triangles. Emde et al. (initial cohort)'; closed circles, Emde et al. (second longitudinal cohort)'. (B)Open squares, Bell and Ainsworth'; closed triangles, Snow et al."; open triangles, Roe4'; closed circles, Emde et al. (second longirudinal cohort)'; open circles. Hubbard and van IJZendoorn"; crosses, SI. James-Roberts" .
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marked during the crying peak; fourth, there is a large degree of within-individual variability from day to day; and fifth, early crying is not modifiable by differences in caretaking style. The evidence for the first proposition is perhaps the strongest. This pattern has remained robust across different methods of recording, including diaries’. 4. l o , recall interviews , questionnaires” and electronic recordings3, across normal and clinical (colicky) population~”’-~~, and across time]. 4. This robustness is illustrated in Figure lA, in which the pattern from studies covering a sufficiently long period of time and providing sub-monthly breakdowns of data is plotted. Furthermore, all studies covering other periods in the first year support the picture that the early curve is unique to the first three months (Fig. 1B). The presence of the peak in audiotaped recordings, even though the sample recorded (N = 10) is small, adds considerable confidence that this characteristic is real3. Using recall interviews, EMDE and colleagues’ first cohort (Fig. lA, open triangles)-but not their second (closed circles)-show the early rise5. WOLFF14 reports three-monthly values which show a gradual decline for both crying and fussing, but it is unclear whether this exception can be accounted for by elimination of days when an infant was ‘clearly uncomfortable’ and ‘inconsolable’ (p. 81). The evidence for evening clustering is not quite so consistent but nevertheless is substantial. Although using different metrics, all diary studies report clustering during the late afternoon and evening’. 4, 15* 16. This diurnal rhythm may be distinguishable by 10 days of lifet5, is most distinct at the age of peak crying, and becomes progressively less so thereafter’. 4. Unfortunately, SNOW and colleague^'^ do not report whether the diurnal rhythm is ever apparent again up to 26 months. Apparently this characteristic is unique to early crying. However, there is a suggestion of increased night crying at the end of the first year, associated with night waking”. REBELSKY and BLACK’S report of audiotape recordings) only describes the earliest (one to three weeks) and Iatest (12
to 13 weeks) within-day distributions, which is likely to have missed the peak clustering time. In a 24-hour comparison of 10 six-week-old infants’*, there was more evening cry/fussing behaviour by diary and negative vocalizations by audiotape than during the night and daytime. There appear to be no reports of direct behavioural observations during the evening hours. Since evening (1 8.00 to 24.00 hours) crying constitutes about 40 per cent of the totalll. 16, conclusions based on behavioural observations limited to the daytime could be substantially biased. There is no dispute about the large between-subject differences. With few exceptions, this variability is greatest at the age of peak crying1*3.4,or in the first quarter of the first year2. 5 * 19. REBELSKY and BLACK3 noted that between-subject variability was greater than within-subject variability, implying that infants are more like themselves than they are like each other. Measures of within-subject variability from day to day are less commonly reported, often because investigators are more interested in stability of ranking over extended periods of time. REBELSKY and BLACK3 described it as ‘very high’, although ‘slightly lower’ than betweensubject variability. This variability means that crying patterns of individual infants are likely to differ considerably from the smooth pattern of the average values for groups represented in Figure 1. This is illustrated in Figure 2, in which the mean and standard error values of duration of cry/fuss for the group are superimposed on the values obtained for each of the individuals4. Studies aiming to determine biological or behavioural factors affecting this pattern need to take account of this variability. Furthermore, short-term improvement in response to a clinical intervention may not necessarily indicate that the intervention is effective. As a result, timing and length of observations and sample size are crucial for evaluating reports of group differences, age-related trends and ‘successful’ clinical trials. Perhaps most controversial is the proposition that early crying is not modifiable by caretaking style. This would
seem to fly in the face of studies in which relatively discrete variables such as maternal latency to respond’, or carrying4 and broad variables like cultural caretaking styles20.2ihave been related to differences in crying behaviour (see also reference^'^. Most of the apparent contradiction is resolved when the proposition is limited t o the pattern, as distinct from the amount, of early crying. For example EMDE and colleagues’ conclude that ‘since fussiness occurred . . . in all of the babies observed in both our longitudinal studies, it seems unlikely that environmental factors, such as variations in mothering or changes in the surround, play a major role in its emergence, maintenance, o r decline’. A similar position has been taken by most authors reporting longitudinal data’. *. lo. 15, commentators6. 26 and cliniciansI3. 27. The apparent robustness of this curve has helped to define possible interpretations of its origins, and of the function of early crying. It has been proposed that this pattern reflects ‘biobehavioural shifts’ during the first year of life’. 5 . 26-28. In this framework, the crying curve is compared with other biologically based behavioural rhythms and is shown to be consistent with a picture of increasing regularity and rhythmicity in state regulation’. 5 * 26, 28, 29. For example, the six-week peak corresponds closely to dramatic shifts in states of wakefulness, characterized by a rapid increase in ‘alert activity’ and reciprocal decline of ‘alert i n a ~ t i v i t y ” ~Since . the pattern is common, predictable, and independent of caretaking style, it is considered to reflect physiological maturational changes’. This interpretation is consistent with the picture of a changing r61e for the cry signal. For most authors, the maternal tendency to respond to crying remains stable throughout the first year’. 5 - 30-32 and may be established prenatally3’. The cry signal may begin as a relatively independent and undifferentiated reflection of physiological state (‘expressive’ crying), whereas later it becomes more tied to maternal response and more intentional ( ‘ c o m m ~ n i c a t i v e ~ ~This - ~ ~ )distinction . is of some importance, because otherwise it is difficult to explain the diminution at
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Age (Weeks) Fig. 2. Cry/fuss duration by week of age of 50 infants. with superimposed mean and SE values for whole group. (Data from Huntiker and Barr control group‘.)
three months in the face of relative constancy of maternal responses. Physiologically, the change may reflect the emergence of new capacities for state regulation and communication, which replace or obviate the ‘need’ for crying to function as a signal which ‘recruits’ external regulatory influences3’. Nevertheless, the mechanisms underlying this behavioural change remain a matter for speculation. Understandably, past studies have provided undifferentiated, quantitative descriptions which may obscure important differences ‘within’ the crying curve. One of the most interesting questions is whether it is really one curve or the convolution of two or more curves. A number of candidate ‘components’ might contribute, each of which implicate fundamental principles of behavioural organization. For example, it is unclear whether subgroups of infants contribute differently to the over-all pattern. The most intensively studied have been infants with colic, yet it remains unclear whether
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Fig. 3. Cry/fussing duration by week of age of 49 infants given ‘supplemental carrying’, showing absence of six-week peak seen in control group (Fig. 2 ) and other studies (Fig. 1). (Data are from Hunziker and Barr4.)
360
their crying is qualitatively different, and whether there is a different mechanism underlying ita. Second, it is unclear whether the diurnal peak and the twomonth peak reflect the same underlying process or two independent processes. Such a distinction is suggested by the fact that a temperament index at two weeks predicts daytime, but not evening, crying at six weeks16. Similarly, the apparent stability of crying after three months may actually reflect two dynamic processes, namely a decline in ‘expressive’ crying coexistent with an increase in ‘communicative’ crying. Third, ‘crying’ and ‘fussing’ are seldom clearly delineated, but they both may be qualitatively and functionally distinct, each contributing differently to the crying curve. Two strategies are likely to contribute to the necessary ‘parsing’ of component contributions and mechanisms, namely qualitative behavioural studies of the ‘crying act’, and comparative studies. Recent research has suggested that studies
conducted at these molar levels of description is both feasible and potentially valuable. Descriptions of the ‘crying act’ take account of the fact that crying is not simply an auditory signal, but part of more complicated vocal-motoric-communicative activity. For example HOPKINSand PALTHE39 define crying and fussing in the context of behavioural state concepts, using both vocal and facial features, and relating cries t o context (presence or absence of mother). Interestingly, fussing thus defined appeared for the first time at six weeks. After three months, ‘interrupted’ fussing (rapid alternations between fussing and cooing) appeared; but only in the absence of mother. This suggests that crying and fussing may indeed contribute independently to the ‘normal curve’, that determinants of crying may more accurately be understood as determinants of infant state, and that context may be critical even at three months. Although difficult, comparative and even experimental studies of biological and behavioural determinants of crying in natural contexts are feasible. In a randomized controlled trial, increased carrying beyond that typical in Western society effectively reduced crying and fussing by 43 per cent at six weeks, and by 54 per centin the evening4. Furthermore, the peak at six weeks was eliminated (Fig. 3), while the evening clustering remained. This study confirmed experimentally the substantial importance of caretaking style, but also challenged the extent to which the crying curve is ‘normal’ beyond the context in which it is embedded. These and other findings remind us, despite the replications across studies, that what we really know about the normal crying curve is actually quite limited. While important progress has. occurred in microlevel descriptions of cry acoustics and listener perception, these studies generally neglect developmental changes and crying ‘in context’. While considerable consensus has been achieved concerning real-life macrolevel characteristics across time, these descriptions generally ignore qualitative distinctions and seldom employ comparative techniques to permit testing of putative mechanisms, especially in real-life
contexts. Nevertheless, such gaps are amenable to systematic investigation, and hold the promise of deeper understanding of this essential early human behaviour.
RONALDG. BARR Montreal Children’s Hospital, 2300 Tupper Street, Montreal, Quebec H3H IP3. Acknowledgements The author would like to thank Ms. Sara McMullan for technical and graphics support; Drs. Heinz Spiess and Urs Hunziker for help in generating Figures 2 and 3; and Drs. Jim Green, Fabia Franco and Anton Miller for critical reviews of versions of the manuscript. The author is supported by a grant from the Medical Research Council of Canada, the W. T. Grant Faculty Scholar Award, the Detweiler Travelling Fellowship (Royal College of Physicians and Surgeons, Canada), and an appointment as Visiting Scholar to the Netherlands Institute for Advanced Studies in the Social Sciences and Humanities. This is publication No. 90-008 of the McGill University-Montreal Children’s Hospital Research Institute.
14.
15. 16.
17.
387-394. 18. Barr. R. G., Kramer, M.
S., Boisjoly, C., McVey-White, L., Pless, I. B. (1988) ‘Parental diary of infant cry and fuss behaviour.’ Archives of Disease in Chifdhood, 63,
385387. 19. Hubbard. F. 0. A., van ljzendoorn, M. H. (1989) ‘Does maternal unresponsiveness
20.
References 1. Brazelton. T. B. (1962) ‘Crying . - in infancy.’ Pediatrics. 29, 579-588. 2. Bell, S. M.. Ainsworth, D. S. (1972) ‘Infant crying and maternal responsiveness.’ Child Development, 43, 1171-1190. 3. Rebelsky. F., Black, R. (1972) ‘Crying in infancy.’ Journal of Genetic Psychology, 121, 49-57. 4. Hunziker, U. A., Barr, R. G. (1986) ‘Increased
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carrying reduces infant crying: a randomized controlled trial.’ Pediatrics, 77, 641-648. Emde, R. N.. Gaensbauer. T. J., Harmon, R. J . (I 976) Emotional Expression in I nfancy: A Biobehavioral Study. New York: International University Press. pp. 80-85. Bax, M. (1975) ‘Clinical analysis of the cry.’ Developmental Medicine and Child Neurology, 17, 799-801. Murphy, E. A. (1972) ‘The normal, and the perils of the sylleptic argument .’ Perspectives in Biology and Medicine, Is, 566-582. Barr, R. G. (1989) ‘Recasting a clinical enigma: the problem of early infant crying.’ In Zelazo. P. H.. Barr. R. G. (Eds.) Challennes to Developmental Paradigms.. New -York: Lawrence Erlbaum. pp. 43-64. Lester, B. M.. Boukydis. C. F. Z. (Eds.) (1985) Infant Crying; Theoretical and Research Perspecfives. New York: Plenum. Wessel, M. A., Cobb. J. C.. Jackson, E. B., Harris, G. S., Detwiler. A. C. (1954) ‘Paroxysmal fussing in infancy, sometimes called “colic”.’ Pediatrics, 14, 421-434. St. James-Roberts, I. (1989) ‘Persistent crying in the first year of life.’ Posterpresentedat the 10th Biennial Meeting of the International Society for the Study of Behavioral Development, Jyvaskyla, Finland. July 9-13. Illingworth, R. S. (1954) ‘ “Three-months colic.” ’ Archives in of Disease in Childhood, 29, 165-174. Paradise, J. L. (1966) ‘Maternal and other factors in the etiology of infantile colic.’
Journal of the American Medical Association, 197, 181-199. Wolff, P. H. (1987) The Development of Behavioral States and the Expression of Emotion in Early Infancy: New Proposals for Investigation. Chicago: University of Chicago Press. Bernal, J. (1972) ‘Crying during the first ten days of life.’ Developmental Medicine and Child Neurology, 14, 362-372. Barr, R. G., Kramer, M., Pless, I. B., Boisjoly, C.. Leduc, D. (1989) ‘Feeding and temperament as determinants of early infant cry/fuss behavior.’ Pediatrics, 84, 5 14-521. Snow, M. E., Jacklin, C. N., Maccoby, E. E. (1980) ‘Crying episodes and sleep-wakefulness transitions in the first 26 months of life.’ Infant Behavior and Development, 3,
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increase infant crying? A critical replication of the 1972 Bell and Ainsworth study.’ Presented at the Third International Workshop on Infant Cry Research. Hanasaari, Finland, July 13-18. Caudill, W., Weinstein, H. (1969) ‘Maternal care and infant behavior in Japan and America.’ Psychiatry. 32, 12-43. Landau, R. (1982) ‘Infant crying and fussing: findings from a cross-cultural study.’ Journal of Cross-Cultural Psychology. 13, 427-444. Sander, L. W., Stechler, G., Burns, P., Julia, H. (1970) ‘Early mother-infant interaction and 24-hour patterns of activity and sleep.’ Journal of the American Academy of Child Psychiatry. 9, 103-123. Thoman, E. B., Acebo, C., Becker, P. T. (1983) ‘Infant crying and stability in the motherinfant relationship: a systems analysis.’ Child Development, 54, 653-659. Crockenberg, S., Smith, P. (1982) ‘Antecedents of mother-infant interaction and infant irritability in the first three months of life.’ Infant Behavior and Development, 5,
105-1 19. 25. Roe, J. M., Feldrnan, S. S., Drivas, A. (1988)
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27. 28.
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30.
‘Interactions with three-month-old infants: a comparison between Greek mothers and institutional caregivers.’ International Journal of Behavioral Development, 11, 359-367. Lester, B. M. (1985) ‘There’s more to crying than meets the ear.’ I n Lester, B. M., Boukydis, C. F. Z . (Eds.) InJan1 Crying: Theoretical and Research Perspectives. New York: Plenum. pp. 1-27. Illingworth. R. S. (1955) ‘Crying in infants and children.’ British Medical Journal, 1, 75-78. Parmelee. A. H., Stern: E. (1972) ‘Development of states in infants. In Clemente, C. D., Purpura. D. P., Mayer, F. E. (Eds.) Sleep and the Maturing Nervous System. New York: Academic Press. pp. 199-215. Prechtl, H. F. R. (1984) ‘Continufty and change in early neural development. In Prechtl. H. F. R. (Ed.) Continuity of Neural Functions from Prenatal to Postnatal Life. Clinics in Developmental Medicine, No. 94. London: S . I .M. P. with Blackwell Scientific; Philadelphia: Lippincott. Fish, M., Crockenberg. S. (1981) ‘Correlates and antecedents of nine-month infant behavior
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and mother-infant interaction.’ Infanf Behavior and Development, 4, 69-8 1. 31. Moss, H. A. (1974) ‘Communication in motherinfant interaction.’ I n Krames, L., Pliner, P.. Alloway. T. (Eds.) Nonverbal Communicafion. New York: Plenum. pp. 171-191. 32. Minde. K.. Trehub, S.. Corter, C.. Boukydis. C., Celhoffer, L., Marton, P. (1978) ‘Motherchild relationships in the premature nursery: an observation study.’ Pediatrics, 61, 373-379. 33. D’Odorico, L.. Franco,
F., Vidotto, G. (1985) ‘Temporal characteristics in infant cry and non-cry vocalizations.’ Language and Speech,
28, 29-46.
34. Franco, F. (1984) ‘Differences in manner of
phonation of infant c r i y relationship to communicative context. Language and Speech, 27, 59-78. 35. D’Odorico. L. (1984) “on-segmental features in prelinguistic communications: an analysis of some types of infant cry and non-cry vocalizations.’ Journal of Child Language, 11, 17-27. 36. Gekowski, M. J., Rovee-Collier, C. K., CamlliRabinowitz, V. (1983) ‘A longitudinal analysis
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of inhibition of infant distress: the origins of social expectations?’ Infant Behavior and Development, 6, 339-351. 37. Thompson, R. A., Leger, D. W.. Walker, J. A., Garbin, C. P. (1988) ‘Infant cries as graded or discrete socioemotional signals.’ I n Oster, H. (Chair) Emotionalfipressions in Infants: New Perspectives on an Old Controversy. Symposium conducted at the meeting of the International Conference on Infant Studies, Washington, D.C. 38. Hofer, M. (1987) ‘Early social relationships: a sychobiologist’s view.’ Child Development,
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8, 633-647. 39. Hopkins, B., Palthe, T. van W. (1987) ‘The
development of the crying state during early infancy.’ Developmental Psychobiology, 20,
165-1 75. 40. Bloom, K., McDowell,
E. E. (1972) ‘Timesampling caretaker and infant behaviors in the first five weeks of life.’ Journalof Psychology,
80,111-120. 41. Roe. K. V. (1975)
‘Amount of infant vocalization as a function of age: some cognitive implications..’ Child Development, 46,936-94 I .
The Normal Crying Curve: What Do We Really Know?
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DESCRIPTIONSof behavioural curves exert considerable influence on our way of thinking about development. In recent years there has been increasing interest in infant crying behaviour, both as a developmental phenomenon and as a clinical problem (commonly referred to as ‘colic’). Crying is usually described in terms of a behavioural curve, characterized by an early increase to a peak during the second month, a decrease until about four months, and little change thereThe pattern raises interesting but unanswered questions about biological and behavioural factors affecting crying. Following their own extensive study of the phenomenon, EMDE and colleaguesS concluded that ‘early fussiness is puzzling and does seem to be unexplained’ (p. 84). Despite (or perhaps because of) the lack of explanation, the curve is usually interpreted as describing the normal pattern of crying. As such, it provides a potential basis for understanding infant development and for approaching clinical complaints’s 6. The word ‘normal’ is fraught with ambiguity, especially in the clinical context’. As an adjective, it implies (1)’ that the noun it modifies refers to an entity that is in some sense natural, appropriate, or optimal, perhaps even necessary and unchangeable; and (2) that 2 9 5 9
356
a distinction can be made between that which is normal and abnormal. These connotations represent potentially important claims, but not ones which will be discussed here (see BARR~). In the present context, ‘normal’ refers only t o that which is described as the crying of normal (non-pathological) infants. The usefulness of the ‘normal crying curve’ depends on the accuracy and completeness with which it describes crying behaviour, for it constrains the possible interpretations of the origin and meaning of early crying. Despite considerable consensus about its main characteristics, important questions remain about what process (or processes) the ‘normal curve’ describes. Stimulated by the technique of cry spectrographjl, interest has focused on microlevel descriptions of cry morphology and the importance of specific cry features for listener response or diagnostic prediction (for a review, see LESTERand BOUKYDIS’).By and large, however, developmental changes have involved more macrolevel descriptions of duration and frequency over hours, days, weeks or months, based primarily on diaries, with occasional support from short-term direct observations and audiorecordings. From these studies, there are five propositions about which most observers agree: first, there is a progressive increase in crying which peaks in the second month and then gradually decreases; second, there is a diurnal rhythm, typified by clustering during the evening hours, most marked during peak crying in the second month; third, there is considerable between-individual variability, again most
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Fig. I . A (above) and B (below). Patterns of cry (and/or fuss) behaviour over first three months (A) or first two years (B)of life. Data derived from referenced publications are plotted as percentage of total reported crying for tho1 study. Consequently, patterns. but not amounts of crying, are comparable across studies. (A) Closed diamonds, Bloom and McDo welt'; closed squares, Rebelsky and Black'; open diamonds, Hunziker and Barr (control group)'; open squares, Brazelton open triangles. Emde et al. (initial cohort)'; closed circles, Emde et al. (second longitudinal cohort)'. (B)Open squares, Bell and Ainsworth'; closed triangles, Snow et al."; open triangles, Roe4'; closed circles, Emde et al. (second longirudinal cohort)'; open circles. Hubbard and van IJZendoorn"; crosses, SI. James-Roberts" .
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marked during the crying peak; fourth, there is a large degree of within-individual variability from day to day; and fifth, early crying is not modifiable by differences in caretaking style. The evidence for the first proposition is perhaps the strongest. This pattern has remained robust across different methods of recording, including diaries’. 4. l o , recall interviews , questionnaires” and electronic recordings3, across normal and clinical (colicky) population~”’-~~, and across time]. 4. This robustness is illustrated in Figure lA, in which the pattern from studies covering a sufficiently long period of time and providing sub-monthly breakdowns of data is plotted. Furthermore, all studies covering other periods in the first year support the picture that the early curve is unique to the first three months (Fig. 1B). The presence of the peak in audiotaped recordings, even though the sample recorded (N = 10) is small, adds considerable confidence that this characteristic is real3. Using recall interviews, EMDE and colleagues’ first cohort (Fig. lA, open triangles)-but not their second (closed circles)-show the early rise5. WOLFF14 reports three-monthly values which show a gradual decline for both crying and fussing, but it is unclear whether this exception can be accounted for by elimination of days when an infant was ‘clearly uncomfortable’ and ‘inconsolable’ (p. 81). The evidence for evening clustering is not quite so consistent but nevertheless is substantial. Although using different metrics, all diary studies report clustering during the late afternoon and evening’. 4, 15* 16. This diurnal rhythm may be distinguishable by 10 days of lifet5, is most distinct at the age of peak crying, and becomes progressively less so thereafter’. 4. Unfortunately, SNOW and colleague^'^ do not report whether the diurnal rhythm is ever apparent again up to 26 months. Apparently this characteristic is unique to early crying. However, there is a suggestion of increased night crying at the end of the first year, associated with night waking”. REBELSKY and BLACK’S report of audiotape recordings) only describes the earliest (one to three weeks) and Iatest (12
to 13 weeks) within-day distributions, which is likely to have missed the peak clustering time. In a 24-hour comparison of 10 six-week-old infants’*, there was more evening cry/fussing behaviour by diary and negative vocalizations by audiotape than during the night and daytime. There appear to be no reports of direct behavioural observations during the evening hours. Since evening (1 8.00 to 24.00 hours) crying constitutes about 40 per cent of the totalll. 16, conclusions based on behavioural observations limited to the daytime could be substantially biased. There is no dispute about the large between-subject differences. With few exceptions, this variability is greatest at the age of peak crying1*3.4,or in the first quarter of the first year2. 5 * 19. REBELSKY and BLACK3 noted that between-subject variability was greater than within-subject variability, implying that infants are more like themselves than they are like each other. Measures of within-subject variability from day to day are less commonly reported, often because investigators are more interested in stability of ranking over extended periods of time. REBELSKY and BLACK3 described it as ‘very high’, although ‘slightly lower’ than betweensubject variability. This variability means that crying patterns of individual infants are likely to differ considerably from the smooth pattern of the average values for groups represented in Figure 1. This is illustrated in Figure 2, in which the mean and standard error values of duration of cry/fuss for the group are superimposed on the values obtained for each of the individuals4. Studies aiming to determine biological or behavioural factors affecting this pattern need to take account of this variability. Furthermore, short-term improvement in response to a clinical intervention may not necessarily indicate that the intervention is effective. As a result, timing and length of observations and sample size are crucial for evaluating reports of group differences, age-related trends and ‘successful’ clinical trials. Perhaps most controversial is the proposition that early crying is not modifiable by caretaking style. This would
seem to fly in the face of studies in which relatively discrete variables such as maternal latency to respond’, or carrying4 and broad variables like cultural caretaking styles20.2ihave been related to differences in crying behaviour (see also reference^'^. Most of the apparent contradiction is resolved when the proposition is limited t o the pattern, as distinct from the amount, of early crying. For example EMDE and colleagues’ conclude that ‘since fussiness occurred . . . in all of the babies observed in both our longitudinal studies, it seems unlikely that environmental factors, such as variations in mothering or changes in the surround, play a major role in its emergence, maintenance, o r decline’. A similar position has been taken by most authors reporting longitudinal data’. *. lo. 15, commentators6. 26 and cliniciansI3. 27. The apparent robustness of this curve has helped to define possible interpretations of its origins, and of the function of early crying. It has been proposed that this pattern reflects ‘biobehavioural shifts’ during the first year of life’. 5 . 26-28. In this framework, the crying curve is compared with other biologically based behavioural rhythms and is shown to be consistent with a picture of increasing regularity and rhythmicity in state regulation’. 5 * 26, 28, 29. For example, the six-week peak corresponds closely to dramatic shifts in states of wakefulness, characterized by a rapid increase in ‘alert activity’ and reciprocal decline of ‘alert i n a ~ t i v i t y ” ~Since . the pattern is common, predictable, and independent of caretaking style, it is considered to reflect physiological maturational changes’. This interpretation is consistent with the picture of a changing r61e for the cry signal. For most authors, the maternal tendency to respond to crying remains stable throughout the first year’. 5 - 30-32 and may be established prenatally3’. The cry signal may begin as a relatively independent and undifferentiated reflection of physiological state (‘expressive’ crying), whereas later it becomes more tied to maternal response and more intentional ( ‘ c o m m ~ n i c a t i v e ~ ~This - ~ ~ )distinction . is of some importance, because otherwise it is difficult to explain the diminution at
6 r 3
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Age (Weeks) Fig. 2. Cry/fuss duration by week of age of 50 infants. with superimposed mean and SE values for whole group. (Data from Huntiker and Barr control group‘.)
three months in the face of relative constancy of maternal responses. Physiologically, the change may reflect the emergence of new capacities for state regulation and communication, which replace or obviate the ‘need’ for crying to function as a signal which ‘recruits’ external regulatory influences3’. Nevertheless, the mechanisms underlying this behavioural change remain a matter for speculation. Understandably, past studies have provided undifferentiated, quantitative descriptions which may obscure important differences ‘within’ the crying curve. One of the most interesting questions is whether it is really one curve or the convolution of two or more curves. A number of candidate ‘components’ might contribute, each of which implicate fundamental principles of behavioural organization. For example, it is unclear whether subgroups of infants contribute differently to the over-all pattern. The most intensively studied have been infants with colic, yet it remains unclear whether
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Age (Weeks)
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Fig. 3. Cry/fussing duration by week of age of 49 infants given ‘supplemental carrying’, showing absence of six-week peak seen in control group (Fig. 2 ) and other studies (Fig. 1). (Data are from Hunziker and Barr4.)
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their crying is qualitatively different, and whether there is a different mechanism underlying ita. Second, it is unclear whether the diurnal peak and the twomonth peak reflect the same underlying process or two independent processes. Such a distinction is suggested by the fact that a temperament index at two weeks predicts daytime, but not evening, crying at six weeks16. Similarly, the apparent stability of crying after three months may actually reflect two dynamic processes, namely a decline in ‘expressive’ crying coexistent with an increase in ‘communicative’ crying. Third, ‘crying’ and ‘fussing’ are seldom clearly delineated, but they both may be qualitatively and functionally distinct, each contributing differently to the crying curve. Two strategies are likely to contribute to the necessary ‘parsing’ of component contributions and mechanisms, namely qualitative behavioural studies of the ‘crying act’, and comparative studies. Recent research has suggested that studies
conducted at these molar levels of description is both feasible and potentially valuable. Descriptions of the ‘crying act’ take account of the fact that crying is not simply an auditory signal, but part of more complicated vocal-motoric-communicative activity. For example HOPKINSand PALTHE39 define crying and fussing in the context of behavioural state concepts, using both vocal and facial features, and relating cries t o context (presence or absence of mother). Interestingly, fussing thus defined appeared for the first time at six weeks. After three months, ‘interrupted’ fussing (rapid alternations between fussing and cooing) appeared; but only in the absence of mother. This suggests that crying and fussing may indeed contribute independently to the ‘normal curve’, that determinants of crying may more accurately be understood as determinants of infant state, and that context may be critical even at three months. Although difficult, comparative and even experimental studies of biological and behavioural determinants of crying in natural contexts are feasible. In a randomized controlled trial, increased carrying beyond that typical in Western society effectively reduced crying and fussing by 43 per cent at six weeks, and by 54 per centin the evening4. Furthermore, the peak at six weeks was eliminated (Fig. 3), while the evening clustering remained. This study confirmed experimentally the substantial importance of caretaking style, but also challenged the extent to which the crying curve is ‘normal’ beyond the context in which it is embedded. These and other findings remind us, despite the replications across studies, that what we really know about the normal crying curve is actually quite limited. While important progress has. occurred in microlevel descriptions of cry acoustics and listener perception, these studies generally neglect developmental changes and crying ‘in context’. While considerable consensus has been achieved concerning real-life macrolevel characteristics across time, these descriptions generally ignore qualitative distinctions and seldom employ comparative techniques to permit testing of putative mechanisms, especially in real-life
contexts. Nevertheless, such gaps are amenable to systematic investigation, and hold the promise of deeper understanding of this essential early human behaviour.
RONALDG. BARR Montreal Children’s Hospital, 2300 Tupper Street, Montreal, Quebec H3H IP3. Acknowledgements The author would like to thank Ms. Sara McMullan for technical and graphics support; Drs. Heinz Spiess and Urs Hunziker for help in generating Figures 2 and 3; and Drs. Jim Green, Fabia Franco and Anton Miller for critical reviews of versions of the manuscript. The author is supported by a grant from the Medical Research Council of Canada, the W. T. Grant Faculty Scholar Award, the Detweiler Travelling Fellowship (Royal College of Physicians and Surgeons, Canada), and an appointment as Visiting Scholar to the Netherlands Institute for Advanced Studies in the Social Sciences and Humanities. This is publication No. 90-008 of the McGill University-Montreal Children’s Hospital Research Institute.
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