Lecture 5.docx

Lecture 5: The Ontogeny of Play – The ‘why’ of Development The Two Steps in the Study of Development Describing the components of the behavior and how they change with age E.g., Play in kittens peaks around 12 weeks, then decreases in frequency What are the mechanisms that produce those changes? The...

Lecture 5: The Ontogeny of Play – The ‘why’ of Development The Two Steps in the Study of Development Describing the components of the behavior and how they change with age E.g., Play in kittens peaks around 12 weeks, then decreases in frequency What are the mechanisms that produce those changes? The Mechanisms that Produce Change with Age Behavior is built-in (instinctive or innate) Behavior is learned over time Innate Behaviors: Suckling in newborns Migration Hunting instincts Learned Behaviors: Language acquisition Social skills Domesticated behavior in pets Trained dolphins Limits to the Innate-Learned Dichotomy Absence of learning does not mean that experience is not important in shaping the behavior Chick eating its first worm If reared with a collar around its neck so that the chick cannot see its toes in the first few days after hatching, it will not eat worms! The presence of learning does not mean the absence of innate predispositions Susan Mineka’s Experiment: Observational learning (1) Before exposure to fear of snakes A captive monkey will reach over a plastic snake for food (2) Exposure to fear of snakes A captive monkey views another monkey expressing fear at the sight of a snake (3) After exposure to fear of snakes Monkey expresses fear of the plastic snakes But is the video exposed naïve monkey is exposed to a monkey reacting fearfully toward a flower, the observer monkey does not learn to fear flowers! We tend to be prepared to learn some things, but not others Teasing Out Non-Learning Factors Intrinsic changes in capability Chickens peck at items on the ground to obtain their food Newly hatched chicks are not very good at pecking Chicks wearing goggles with offset lenses Indirect environmental influences Development of gull displays The Intercalation of Intrinsic and Experiential Factors Jerry Hogan and the development of behavior systems Dust bathing in chickens Effects of deprivation Diurnal cycling begins by about 3 weeks irrespective of experience Effect of Substrate after Dustbathing Behavior is Consolidated Sand = preference for sand Sawdust = preference for sawdust Coal dust = preference for coal dust So is Play Prefunctional or Functional? Sex differences in the play of rates What makes males different to females? From a common starting point, the sexual organ system differentiate Remove the gonads before this differentiation begins and females will look like females and so do males That is, in mammals, the female is the default condition Gonadal hormones (e.g., testosterone) are necessary to organize male organ systems Organizational Effects of Testosterone Newborn male + castration = Exhibits female behavior Newborn female + testosterone = Exhibits male behaviors Early in development hormones organize tissue. After maturity hormones activate that tissue Sex Differences in Play Fighting Playful attacks – The lower frequency of play in females is the default condition (male typical levels depend on exposure to testosterone in the perinatal period) Frequency of playful attacks with age in rats Peaks at 41-45 days; decreases rapidly in both sexes Hormone induced changes in the frequency of play Playful Defense – In males the change in defense at puberty depends on testosterone exposure in the perinatal period, but females are not default condition, as circulating gonadal hormones are needed to suppress the change at puberty Changes in the use of playful defense tactics with age Hormone induced changes in playful defense tactics While it is generally true that in mammals, females are the default condition, this is not true for all traits. It is Also the Case that Some Sex Differences Can be Variable Sex differences in the amount of play are not found in all studies. Why? First, the partner with whom they are tested can affect how much the animals play, and second, this difference is not present in all strains of rats Within strains in which sex differences are present, the magnitude of the difference can vary depending on the rearing condition. Juveniles reared in same sex pairs show the least, and those reared in mixed sex groups show the most That is, hormones wire up the brain in a sex-differentiated manner, but the rearing condition can affect the degree to which those differences in wiring are expressed behaviorally Sex differences show that the basic organization of play, like dust bathing in chickens, is prefunctional, but some components can be modified by experience The amount of play initiated (playful attacks) can be altered by early rearing experiences (e.g., amount of maternal contact, premature weaning) Strain Differences in Play Attacks: Male & Female Sprague Dawley = Most attacks Defense Tactics: Evasion = Male/Female Sprague Dawley Complete Rotation = Male Wistar & Female Sprague Dawley Long Evans (LE) Rats Tested with Sprague Dawley (SD) Partners Each strain retains its strain-typical preference irrespective of the strain of the play partner But what if LE are reared with SD partners? The two strains modify their preference to converge towards that of the other strain That means that play experience in the tine shortly after weaning functionally shapes the development of playful defense Long Evans (LE) Rats Reared Alone Over the Sensitive Period Rats reared in isolation initiated more playful attacks The development of strain-typical defense tactics are prefunctional (does not require experience) The convergence between LE and SD tactics when reared together arises from each adapting to an atypical partner The Rule seems to be, ‘develop the strain typical pattern unless you encounter a deviant social environment’ But there are limits. For some strains, large differences cannot be overcome by rearing experiences The Role of Functional Experience Rearing experiences can affect this markedly, but defense tactics are more resistant to changes due to experience If the attack and defense is too vigorous, the partner will stop playing with you, so based on experience you learn to restrain your action to a level that keeps the game going The Ontogeny ‘Why’ of Play The basic play behavior system develops prefunctionally and is complete by the onset of the juvenile period The Functionally driven modifications give clues about the mechanisms and functions of play