School of Psychology, Birkbeck College

Course PSYC044U (Psychobiology II.) WEEK 2
February 1st 2007

gif
gifThis is just the first 6 pages of the paper handout. Web versions of the other pages in the paper handout (and additional items not on the handout) are accessible from the side index. If you need to print all the pages, you could try the 'pdf' file, but this is quite large and may be difficult to download over a telephone modem.

 

Topics

Neonatal instinctive behaviours and parental behaviours: imprinting, early learning and social development.

  1. Instinctive responses ('Innate releasing mechanisms' or the IRM) in nestling birds: Tinbergen and Perdeck (1950), Bachman, & Chappell (1998), Kilner, Noble, & Davies (1999), Kilner (2001), Hauber et al (2001), Butchart et al. (2003), Madden & Davies, (2006). Goth & Evans (2004) and Barry & Goth (2006) studied innate visual recognition of species in the brush turkey, which has no interactions with its parents.

  2. Rapid and delayed perceptual learning of parental appearance in fowl and of song patterns in songbirds ("Imprinting" - Lorenz, 1937; Hess, 1973; Horn, 1998, 2004; Johnson, 1999; Bolhuis et al., 2000; Bischolf, 2003; Riebel, 2003; Simpson and Vicario, 1996; Hollis et al., 1991; Burley, 2006).

  3. Development of mother-infant attachment in mammals, especially primates; role of maternal and peer interactions on infant and adult behaviour in primates (Harlow, 1970; Lamb et al, 1984; Maestripieri et al, 2000; Maestripieri 2001a,b,c, Maestripieri & Roney, 2006; Steiner et al, 2001; Zeifman, 2001; Gilmer & McKinney, 2003; Machado and Bachevalier, 2003; Farroni et al., 2004, 2005, 2006; Reid et al, 2004).

  4. Theoretical accounts of these imprinting phenomena, mechanisms and functions (Bateson, 1979, 2000; Shettleworth, 1993; general theories e.g. Kraemer, 1992; Hollis et al., 1991; Bateson, 2000, Bolhuis and Honey, 1998; Horn, 2004) - conclusion that they are examples of specialized forms of learning relating in some ways to more general forms of learning and memory.

 

 

Summary

It would be reasonable to expect that the behaviour of newborn animals is governed largely by innate mechanisms. However, Lorenz (1937), an ethologist, discovered that in geese and in other species where the new born are comparatively mobile, the recognition of parental appearance is not fully innate, but rather is strongly influenced by visual experience in the first few days after hatching. Initially it was emphasised that this process of “imprinting” differed from more general forms of learning (see “Feature of Imprinting”, below), but more recently it has been suggested that imprinting is not such a special case, because most forms of learning are influenced by adaptive specializations. That is, particular species are predisposed to learn things which have functional significance for their own life-style. (Bateson, 1990, Shettleworth, 1993).

The work of Harlow (1958) on maternally deprived rhesus monkeys was at one time used to counter the view that primates are born with no instinctive social needs. Newborn rhesus monkeys have a preference for tactile “contact comfort” and well as warmth and motion (Harlow and Suomi, 1970). There is a “sensitive period” of a few weeks after which infant monkeys do not form an attachment. But normal development of the natural “species-specific” rhesus monkey behaviours involved in play, mating and maternal behaviour requires experience with peers as well as adequate maternal care in infancy.

(Futher notes are given at pages 2 and 3 of this handout)

 

 

 

Sample Essay

 

“Describe and discuss the early development of social attachments in birds and primates, in the context of interactions between instinct and early forms of learning.”  

 

 

 

 

 

 

PARENT-YOUNG INTERACTIONS IN BIRDS (page 2 of handout)

‘Altricial’ = ‘Nidiculous’ species. The common pattern: parents (usually both) bring food to young in the nest or nesting area. The young must ‘beg’ for food, at the minimum by opening their mouths.

‘Precocial’ = ‘Nidifugous’ species. Familiar in fowl: the young are mobile at birth, and feed themselves, but parents (usually both) perform protective functions.

There are mixtures: in Oystercatchers (Norton-Griffiths, 1969) the young are mobile, but the parents bring food to the next for several days, and may continue to feed the young away from the nest for several months after hatching.

Individual recognition of parents by the young is probably widespread in both cases, also the effect of early social experience on species-recognition (cf the cuckoo for a purely innate case).

“Imprinting” = early learning by the young of the perceptual characteristics of suitably adjacent objects (in nature the parents, but fairly arbitrary artificial objects in experiments). It is studied in precocial species such as chickens and ducks, but the term is sometimes applied more loosely to other species. Attachment is a more general term.

Features of Imprinting(page 2 of handout)

The following features of imprinting were initially emphasised to support the view that the process was not an example of general learning abilities, but a specialized functional adaptation.

  • THE SENSITIVE PERIOD - imprinting is to a large degree limited to the first few days of life. (The ‘CRITICAL RERIOD’ is a stronger version.)

  • Imprinting is INSTANTANEOUS - it is very rapid, but it is also associated with changes in social development that are more gradual.

  • Imprinting is IRREVERSIBLE - not quite, but after a certain age the effects are very difficult to change.

  • Early imprinting has important effects on MATE CHOICE, which takes in adulthood. However, it is believed that this SEXUAL IMPRINTING occurs rather later in life than the initial FILIAL IMPRINTING which influences the first social attachment, and in some species sexual imprinting is influenced by interactions with siblings. (see Bateson, 1979, 1990, 2000; Hollis et al, 1991, Bolhuis and Honey, 1998).

A number of theories (e.g. Hess, 1973; Hoffman and Ratner, 1973; Bateson, 1979, 1990, 2000; Shettleworth, 1993) interpret imprinting as the interaction among several other development factors. E.g. the critical, or ‘sensitive’ period ends because imprinting narrows preferences to familiar objects, and the first preference is protected by future escape from novel objects.

Rajecki et al (1978) suggested that ethological theories of imprinting are better at explaining: ‘maltreatment’ effects, the ‘secure base’ effect, and reactions to separation from the imprinted object.

Nevertheless, some current work on imprinting makes use of it in order to study the neurophysiological bases of learning and memory (e.g. Horn, 1985, 2004)

Therefore, it can be regarded as a specialized form of learning, supporting the interaction between learning and innate factors in development.

A link between parental behaviour in birds and that in mammals including primates is given by the importance of the hormone prolactin in both cases (Bole-Teysot et al., 1998; Riddle et al., 1935; Ziegler, 2000; Schradin et al., 2003). Raised prolactin levels are associated with parental care giving in both males and females in species where both sexes are involved. Human fathers with higher prolactin levels and lower testosterone are more responsive to infant cries (Fleming et al., 2002; see also Burnham et al., 2003).

PARENT-YOUNG INTERACTIONS IN PRIMATES

The starting point is Harlow’s work on maternal deprivation in rhesus monkeys (Harlow, 1958; discussed in Jolly, 1972, Passsingham, 1982) and most general textbooks. The initial finding is merely a disproof of the view that newborns are a tabula rasa except for basic drives - unless “contact comfort” and more complex social needs are added to ‘basic drives’.

Later work on “surrogate mothers” (artificial objects: Harlow and Suomi, 1970) suggested that -

  • Lactation increases preference

  • Further support for the importance of tactile contact

  • Motion increases preference

  • Temperature is important (cold contact comfort is rejected.)

  • There is a ‘Sensitive Period’ since after 4 weeks with only a cold surrogate, it is too late for attachment behaviours to be elicited.

Work with surrogates supports the ‘protest and despair’ cycle following loss of the attachment object in primates (Mineka and Suomi, 1978). A temporary increase in attachment behaviours follow re-unions after separation.

Cloth mothers also used to study the “secure-base” effect (Harlow, 1962; Rajecki et al, 1978) - the secure base leads to increased exploration and investigation of novel objects, especially in the 20-40 day period (rhesus).

But, the cloth mother as the only companion is no basis for adult social behaviour (interactions with peers, mating and mothering: Harlow, 1962; Chamove et al, 1973; Ruppenthal et al. 1976)

Ruppenthal et al, 1976

Females reared without real mothers are inadequate and violent towards their own offspring. Male babies are most neglected. However, contact with peers prior to adulthood increases the probability of adequate mothering behaviour. Also contact with their own infant after a first birth increases the chances of adequate mothering after a second birth.

Rhesus monkeys reared without mothers in groups of 4 tended to have more normal sexual and maternal behaviour than those reared in pairs (Chamove et al, 1973).

Generalizations to humans

Ethological evidence was made use of by Bowlby (1969, 1973; see Rajecki et al, 1978), and Maestripieri (1999a) and Maestripieri and Carroll (1998) continue to make comparisons between human parenting and that of other primates but this is open to criticism. E.g.

Lamb et al (1984)

- evaluated “both the empirical evidence and the interpretation of infant behaviour in terms of principles derived from evolutionary biology” (p.127), looking at the “strange-situation” test in which infant behaviour is observed with the mother alternating with a strange person and rated for quality of attachment. They are against the suggestion that this assesses “whether the infant has developed species-appropriate adaptive behaviour as a result of rearing in an evolutionarily appropriate context”, and conclude that “interpretations in terms of biological adaptation are misguided.” They advocate attention to cultural and sociological differences in rearing patterns and “the study of learned contingencies or social cognition” (p.146).

However, their own finding was that temporal stability in security of attachment is only high when there is stability in family and caretaking circumstances

Gilmer and McKinney (2003) continue to make use of the primate data to develop a general model in which adverse early life events such as disruptions of attachment systems will be risk factors for adult depression, while Machado and Bachevalier (2003) suggest that non- human primate models may in future assist in the understading of human childhood psychopathologies such as autism and Willams syndrome. (See also Moriceau & Sullivan, 2005 and Maestripieri and Roney, 2006). [extracts from the abstracts of these recent papers]

Main sources (Alternatives)

Gleitman, H. (1995/99/2004) Psychology. 4th/5th/6th Edition. Norton, London. pp 534-544/pp576-9/506-10 "Social Development"; pp 379-412/ 405-437/416-7, "The Biological Basis of Social Behaviour".

Harlow, H.F. and Suomi, S.J. (1970) The nature of love simplified. American Psychologist, 25, 161-8.

Jolly, A. (1972/1985) The Evolution of Primate Behaviour. 1st and 2nd edn. Macmillan: London. Chapter 12/14, “Mothers and Infants”.

Lieberman, D. (1993/2000) Learning: Behavior and Cognition. Belmont: Wadsworth. "Learning in an Evolutionary Context". (pp. 361- 392/467-495)

Walker, S.F. (1985) Animal Thought. Routledge & Kegan Paul: London. (Chapter 6 esp. pp. 194-222).

Walker, S.F. (1987) Animal Learning: An Introduction. Routledge & Kegan Paul: London. (Chapter 1; pp 17-26).

Further reading (Alternatives)

Bateson, P.P.G. (1990) Is imprinting such a special case? Philosophical Transactions of the Royal Society, B, 329, 125-131.

Bateson, P. (2000). What must be known in order to understand imprinting?, In Heyes, Cecilia (Ed); Huber, Ludwig (Ed). (2000). The evolution of cognition. Vienna series in theoretical biology. Cambridge, MA, US: The MIT Press. (pp. 85-102: 2 copies at 156.3 EVO in Bk library). ).

Bateson, P. (2003). The promise of behavioural biology. Animal Behaviour, 65, 11-17.

Harlow, H.F. (1958) The nature of love. American Psychologist, 13,673-85.

A complete on-line version of this is provided in the “Classics in History of Psychology Series” (U of York, Canada)

Hinde, R.A. (1970) Animal Behaviour: A Synthesis of Ethology and Comparative Psychology. McGraw-Hill: London. (pp 513-27 on imprinting).

Hollis, K.L., ten Cate, C. and Bateson, P. (1991) Stimulus representation: a subprocess of imprinting and conditioning. Journal of Comparative Psychology, 105, 307-317.

Morton, J. and Johnson, M.H. (1991) CONSPEC and CONLERN: A two- process theory of infant face recognition. Psychological Review, 98, 164-181.

Passingham, R. (1982) The Human Primate. W.H. Freeman: Oxford. ( Chapter 9 "Family", esp. pp. 262-276 on infant attachment: BK short loan at IAV [Pas])

Shettleworth, S.J. (1993) Varieties of learning and memory in animals. Journal of Experimental Psychology: Animal Behaviour Processes, 19, 5-14.

Other references and lecturer’s bibliography - not for further reading

Barry, K. L., & Goth, A. (2006). Call recognition in chicks of the Australian brush-turkey (Alectura lathami). Animal Cognition, 9(1), 47-54.

Bastian, M. L., Sponberg, A. C., Suomi, S. J., & Higley, J. D. (2003). Long-term effects of infant rearing condition on the acquisition of dominance rank in juvenile and adult rhesus macaques (Macaca mulatta). Developmental Psychobiology, 42(1), 44-51.

Bateson, P. & Horn, G (1994) Imprinting and recognition memory - a neural-net model. Animal Behaviour, Vol.48, No.3, Pp.695-715.

Bateson, P.P.G. (1973) Preferences for familiarity and novelty: A model for the simultaneous development of both. Journal of Theoretical Biology, 41, 249-59.

Bateson, P.P.G. (1979) How do sensitive periods arise and what are they for?. Animal Behaviour, 27, 470-86.

Bateson, P.P.G. (1982) Preferences for cousins in Japanese quail. Nature, 295, 236-237.

Bischof, H. J. (2003). Neural mechanisms of sexual imprinting. Animal Biology, 53(2), 89-112.

Bole-Feysot, C., Goffin, V., Edery, M., Binart, N., & Kelly, P. A. (1998). Prolactin (PRL) and its receptor: Actions, signal transduction pathways and phenotypes observed in PRL receptor knockout mice. Endocrine Reviews, 19(3), 225-268

Bolhuis, J. J., & Honey, R. C. (1998). Imprinting, learning and development: from behaviour to brain and back. Trends in Neurosciences, 21(7), 306-311.

Bolhuis, J. J., Cook, S., & Horn, G. (2000). Getting better all the time: improving preference scores reflect increases in the strength of filial imprinting. Animal Behaviour, 59, 1153-1159.

Bowlby, J. (1969) Attachment and Loss. Volume 1 Attachment. Penguin.

Burley, N. T. (2006). An eye for detail: Selective sexual imprinting in zebra finches. Evolution, 60(5), 1076-1085.

Burnham, T. C., Chapman, J. F., Gray, P. B., McIntyre, M. H., Lipson, S. F., & Ellison, P. T. (2003). Men in committed, romantic relationships have lower testosterone. Hormones and Behavior, 44(2), 119-122.

Butchart, S. H. M., Kilner, R. M., Fuisz, T., & Davies, N. B. (2003). Differences in the nestling begging calls of hosts and host- races of the common cuckoo, Cuculus canorus. Animal Behaviour, 65, 345-354.

Chamove, A.S., Rosenblum, L.A. and Harlow, H.F. (1973) Monkeys (Macacca mulatta) raised only with peers: a pilot study. Animal Behaviour, 21, 316-325.

Farroni, T., Johnson, M. H., & Csibra, G. (2004). Mechanisms of eye gaze perception during infancy. Journal of Cognitive Neuroscience, 16(8), 1320-1326.

Farroni, T., Johnson, M. H., Menon, E., Zulian, L., Faraguna, D., & Csibra, G. (2005). Newborns' preference for face-relevant stimuli: Effects of contrast polarity. Proceedings of the National Academy of Sciences of the United States of America, 102(47), 17245-17250.

Farroni, T., Mansfield, E. M., Lai, C., & Johnson, M. H. (2003). Infants perceiving and acting on the eyes: Tests of an evolutionary hypothesis. Journal of Experimental Child Psychology, 85(3), 199-212.

Farroni, T., Menon, E., & Johnson, M. H. (2006). Factors influencing newborns' preference for faces with eye contact. Journal of Experimental Child Psychology, 95(4), 298-308.

Fleming, A. S., Corter, C., Stallings, J., & Steiner, M. (2002). Testosterone and prolactin are associated with emotional responses to infant cries in new fathers. Hormones and Behavior, 42(4), 399-413.

Gilmer, W. S., & McKinney, W. T. (2003). Early experience and depressive disorders: human and non-human primate studies. Journal of Affective Disorders, 75(2), 97-113.

Goodall, J. (1991) Through a Window: Thirty Years with the Chimpanzees of Gombe. London: Penguin.

Goth, A., & Evans, C. S. (2004). Social responses without early experience: Australian brush-turkey chicks use specific visual cues to aggregate with conspecifics. Journal of Experimental Biology, 207(13), 2199-2208.

Hailman, J.P. (1962) Pecking of laughing gull chicks at models of the parental head. Auk, 79, 89-98.

Hamilton, KS, King, AP, Sengelaub, DR, West, MJ (1997) A brain of her own: a neural correlate of song assessment in a female songbird. Neurobiology of Learning and Memory, Vol.68, No.3, Pp.325-332 Is: 1074-7427.

Harlow, H.F. (1958) The nature of love. American Psychologist, 13,673-85.

Harlow, H.F. (1962) The heterosexual affectional system in monkeys. American Psychologist, 17, 1-9.

Hauber, M. E., Russo, S. A., & Sherman, P. W. (2001). A password for species recognition in a brood-parasitic bird. Proceedings of the Royal Society of London Series B-Biological Sciences, 268(1471), 1041-1048.

Healy, S. D. (2006). Imprinting: Seeing food and eating it. Current Biology, 16(13), R501-R502.

Hess, E.H. (1959) Imprinting. Science, 130, 133-141.

Hess, E.H. (1973) Imprinting: Early Experience and the Developmental Biology of Attachment. New York: Van Nostrand (IAW).

Horn, G. (1990) Neural basis of recognition memory investigated through an analysis of imprinting. Philosophical Transactions of the Royal Society, B, 329, 133-142.

Horn, G. (1998). Visual imprinting and the neural mechanisms of recognition memory. Trends in Neurosciences, 21(7), 300-305.

Horn, G. (2004) Pathways of the past: the imprint of memory. Nature Reviews Neuroscience, 5(2):108-20

Ichise, M., Vines, D. C., Gura, T., Anderson, G. M., Suomi, S. J., Higley, J. D., et al. (2006). Effects of early life stress on C-11 DASB positron emission tomography imaging of serotonin transporters in adolescent peer- and mother-reared rhesus monkeys. Journal of Neuroscience, 26(17), 4638-4643.

Insel, T. R. (2000). Toward a neurobiology of attachment. Review of General Psychology, 4(2), 176-185.

Johnson, M.H., Dziurawiec, S., Ellis, H. and Morton, J. (1991) Newborn's preferential tracking of face-like stimuli and its subsequent decline. Cognition, 40, 1-19.

Kilner, R. M. (2001). A growth cost of begging in captive canary chicks. Proceedings of the National Academy of Sciences of the United States of America, 98(20), 11394-11398.

Kilner, R. M., Noble, D. G., & Davies, N. B. (1999). Signals of need in parent-offspring communication and their exploitation by the common cuckoo. Nature, 397(6721), 667-672.

Kraemer, G.W. (1992) A psychobiological theory of attachment. Behavioural and Brain Sciences, 15, 493-541.

Lamb, M.E., Thompson, R.A., Gardner, W.P., Charnov, E.L. and Estes, D.(1984) Security of infantile attachment as assessed in the 'strange situation'. Behavioural and Brain Sciences, 7, 127-71.

Lorenz, K. (1937) The companion in the bird's world. Auk, 54, 245-273.

Lorenz, K. (1952) King Solomon's Ring. London: Methuen.

Lorenz, K. (1967) On Agression. Methuen: London.

Lotem, A (1993) Learning to recognize nestlings is maladaptive for cuckoo Cuculus canorus hosts. Nature, Vol.362, No.6422, Pp.743-745.

Lyon, B. (2007). Mechanism of egg recognition in defenses against conspecific brood parasitism: American coots (Fulica americana) know their own eggs. Behavioral Ecology and Sociobiology, 61(3), 455-463.

Machado, C. J., & Bachevalier, J. (2003). Non-human primate models of childhood psychopathology: the promise and the limitations. Journal of Child Psychology and Psychiatry and Allied Disciplines, 44(1), 64-87.

Madden, J. R., & Davies, N. B. (2006). A host-race difference in begging calls of nestling cuckoos Cuculus canorus develops through experience and increases host provisioning. Proceedings of the Royal Society B-Biological Sciences, 273(1599), 2343-2351.

Maestripieri, D. (1999a). The biology of human parenting: insights from nonhuman primates. Neuroscience and Biobehavioral Reviews, 23(3), 411-422.

Maestripieri, D. (1999b). Fatal attraction: Interest in infants and infant abuse in rhesus macaques. American Journal of Physical Anthropology, 110(1), 17-25.

Maestripieri, D. (2001a). Biological bases of maternal attachment. Current Directions in Psychological Science, 10(3), 79-83.

Maestripieri, D. (2001b). Intraspecific variability in parenting styles of rhesus macaques (Macaca mulatta): The role of the social environment. Ethology, 107(3), 237-248.

Maestripieri, D. (2001c). Is there mother-infant bonding in primates? Developmental Review, 21(1), 93-120.

Maestripieri, D. (2003). Similarities in affiliation and aggression between cross- fostered rhesus macaque females and their biological mothers. Developmental Psychobiology, 43(4), 321-327.

Maestripieri, D. (2005). Early experience affects the intergenerational transmission of infant abuse in rhesus monkeys. PNAS, 102(27), 9726-9729.

Maestripieri, D., & Carroll, K. A. (1998). Child abuse and neglect: Usefulness of the animal data. Psychological Bulletin, 123(3), 211-223.

Maestripieri, D., & Roney, J. R. (2006). Evolutionary developmental psychology: Contributions from comparative research with nonhuman primates. Developmental Review, 26(2), 120-137.

Maestripieri, D., Higley, J. D., Lindell, S. G., Newman, T. K., McCormack, K. M., & Sanchez, M. M. (2006). Early maternal rejection affects the development of monoaminergic systems and adult abusive parenting in rhesus macaques (Macaca mulatta). Behavioral Neuroscience, 120(5), 1017-1024.

Maestripieri, D., Lindell, S. G., Ayala, A., Gold, P. W., & Higley, J. D. (2005). Neurobiological characteristics of rhesus macaque abusive mothers and their relation to social and maternal behavior. Neuroscience and Biobehavioral Reviews, 29(1), 51-57.

Maestripieri, D., Megna, N. L., & Jovanovic, T. (2000). Adoption and maltreatment of foster infants by rhesus macque abusive mothers. Developmental Science, 3(3), 287-293.

McCormack, K., Sanchez, M. M., Bardi, M., & Maestripieri, D. (2006). Maternal care patterns and behavioral development of rhesus macaque abused infants in the first 6 months of life. Developmental Psychobiology, 48(7), 537-550.

Mineka, S. and Suomi, S.J. (1978) Social separation in monkeys Psychological Bulletin, 85, 1376-1400.

Moriceau, S., & Sullivan, R. M. (2005). Neurobiology of infant attachment. Developmental Psychobiology, 47(3), 230-242.

Norton-Griffiths, M. (1969) The organization, control and development of parental feeding in the oyster catcher. Behaviour, 34, 55-114.

Rajecki, D.R., Lamb, M.E., and Obmasher, P. (1978) Towards a general theory of infantile attachment: a comparative reveiw of aspects of the social bond. Behavioural and Brain Sciences, 1, 417-64.

Reid, V. M., Striano, T., Kaufman, J., & Johnson, M. H. (2004). Eye gaze cueing facilitates neural processing of objects in 4- month-old infants. Neuroreport, 15(16), 2553-2555.

Riddle, O., Bates, R.W., & Lahr, E.L. (1935). Prolactin induces broodiness in fowl. American Journal of Physiology, 111: 352-360.

Riddle, O.,Bates, R.E. and Dykshorn, S.W. (1932) A new hormone of the anterior pituitary gland. Proceedings of the Society for Experimental Biology and Medicine, 29, 1211-1212.

Riebel, K. (2003). Developmental influences on auditory perception in female zebra finches - is there a sensitive phase for song preference learning? Animal Biology, 53(2), 73-87.

Ruppenthal, G.C., Arling, G.L., Harlow, H.F., Sackett, G.P. and Suomi, S.J. (1976) A 10-year perspective of motherless mother monkey behaviour. Journal of Abnormal Psychology, 85, 341-49.

Schradin, C., Reeder, D. M., Mendoza, S. P., & Anzenberger, G. (2003). Prolactin and paternal care: Comparison of three species of monogamous new world monkeys (Callicebus cupreus, Callithrix jacchus, and Callimico goeldii). Journal of Comparative Psychology, 117(2), 166-175.

Simpson, H.B and Vicario, D.S. (1996) Male zebra finches can learn male-typical vocalizations from hormone-treated female tutors. Animal Behaviour, 52, 1119-1127.

Slater, P J. B. (1985) An introduction to ethology. Cambridge: Cambridge University Press (supernormal stimulus on page 41).

Steiner, J. E., Glaser, D., Hawilo, M. E., & Berridge, K. C. (2001). Comparative expression of hedonic impact: affective reactions to taste by human infants and other primates. Neuroscience and Biobehavioral Reviews, 25(1), 53-74.

Stevenson, J., Hutchison, R.E., Hutchison, J., Bertram, B.L.R. and Thorpe, W.H. (1970) Individual recognition by auditory cues in the Common Tern (Sterna hirundo) Nature, London, 226, 562-3.

Turati, C., Cassia, V. M., Simion, F., & Leo, I. (2006). Newborns' face recognition: Role of inner and outer facial features. Child Development, 77(2), 297-311.

Waldeck, P., & Andersson, M. (2006). Brood parasitism and nest takeover in common eiders. Ethology, 112(6), 616-624.

Weidman, U. (1961) The stimuli eliciting begging responses in gulls and terns. Animal Behaviour, 9, 115

Winberg, J. (2005). Mother and newborn baby: Mutual regulation of physiology and behavior - A selective review. Developmental Psychobiology, 47(3), 217-229.

Wynne-Edwards, K. E. (2001). Hormonal changes in mammalian fathers. Hormones and Behavior, 40(2), 139-145.

Zeifman, D. M. (2001). An ethological analysis of human infant crying: Answering Tinbergen's four questions. Developmental Psychobiology, 39(4), 265-285.

Ziegler, T. E. (2000). Hormones associated with non-maternal infant care: A review of mammalian and avian studies. Folia Primatologica, 71(1-2), 6-21.