In addition to effects on metabolism and appetite, leptin is a reproductive hormone produced and ... more In addition to effects on metabolism and appetite, leptin is a reproductive hormone produced and secreted by the placenta of many, but not all mammalian species. In mice, in which the placenta does not secrete leptin, exogenously added leptin stimulates invasiveness of early (but not late)-gestation trophoblast cells. We report a similar phenomenon occurs in Myotis lucifugus (little brown myotis), a species in which the placenta synthesizes and secretes leptin. Immunoneutralization of endogenously secreted leptin from cultured M. lucifugus trophoblast cells inhibited the ability of these cells to invade a matrigel matrix. The effect was not due to an inhibitory effect of the antibody on cell proliferation, nor was it a non-specific effect of antibody administration. Cell invasion was significantly reduced in untreated cells obtained from late-gestation placentas, and the antibody had no effect at that time. This occurred despite continued expression throughout gestation of the long (OBRb) and short (OBRa) isoforms of leptin receptor mRNA. This study suggests that an important function of leptin during pregnancy is an effect on trophoblast cell invasiveness, at a time when the placenta is becoming established. That this occurs in two phylogenetically unrelated and distant species, regardless of whether the placenta is a source of secreted leptin, suggests that this is a highly conserved reproductive action of leptin.
The ability to make inductive inferences from sparse data is a critical aspect of human learning.... more The ability to make inductive inferences from sparse data is a critical aspect of human learning. However, the properties observed in a sample of evidence depend not only on the true extension of those properties but also on the process by which evidence is sampled. Because neither the property extension nor the sampling process is directly observable, the learner's ability to make accurate generalizations depends on what is known or can be inferred about both variables. In particular, different inferences are licensed if samples are drawn randomly from the whole population (weak sampling) than if they are drawn only from the property's extension (strong sampling). Given a few positive examples of a concept, only strong sampling supports flexible inferences about how far to generalize as a function of the size and composition of the sample. Here we present a Bayesian model of the joint dependence between observed evidence, the sampling process, and the property extension and test the model behaviorally with human infants (mean age: 15 months). Across five experiments, we show that in the absence of behavioral cues to the sampling process, infants make inferences consistent with the use of strong sampling; given explicit cues to weak or strong sampling, they constrain their inferences accordingly. Finally, consistent with quantitative predictions of the model, we provide suggestive evidence that infants' inferences are graded with respect to the strength of the evidence they observe.
Previous work has demonstrated the importance of both naïve theories and statistical evidence to ... more Previous work has demonstrated the importance of both naïve theories and statistical evidence to children's causal reasoning. In particular, four-year-olds can use statistical evidence to update their beliefs. However, the story is more complex for three-year-olds. Although three-and-a-half-yearolds perform as well as four-year-olds when statistical evidence is theory-neutral, several studies suggest that they do not learn from statistical evidence when a statistically likely cause is inconsistent with their prior beliefs (e.g., . There are at least two possible explanations for younger children's failure to use statistical data to update their beliefs: one (the Information Processing account) suggests that younger children have a fragile ability to reason about statistical evidence; the other (a Prior Knowledge account) suggests that in some domains, younger children have stronger prior beliefs and thus require more evidence before belief revision is rational. To distinguish these accounts, we conducted a two-week training study with three-and-a-halfyear-olds. Children participated in an Information Processing Training condition, a Prior Belief Training condition, or a Control condition.
Given minimal evidence about novel objects, children might learn only relationships among the spe... more Given minimal evidence about novel objects, children might learn only relationships among the specific entities, or they might make a more abstract inference, positing classes of entities and the relations that hold among those classes. Here we show that preschoolers (mean: 57 months) can use sparse data about perceptually unique objects to infer abstract physical causal laws. These newly inferred abstract laws were robust to potentially anomalous evidence; in the face of apparent counter-evidence, children (correctly) posited the existence of an unobserved object rather than revise the abstract laws. This suggests that children's ability to learn robust, abstract principles does not depend on extensive prior experience but can occur rapidly, on-line, and in tandem with inferences about specific relations.
Adults' causal representations integrate information about predictive relations and the possibili... more Adults' causal representations integrate information about predictive relations and the possibility of effective intervention; if one event reliably predicts another, adults can represent the possibility that acting to bring about the first event might generate the second. Here we show that although toddlers (mean age: 24 months) readily learn predictive relationships between physically connected events, they do not spontaneously initiate one event to try to generate the second (although older children, mean age: 47 months, do; Experiments 1 and 2). Toddlers succeed only when the events are initiated by a dispositional agent (Experiment 3), when the events involve direct contact between objects (Experiment 4), or when the events are described using causal language (Experiment 5). This suggests that causal language may help children extend their initial causal representations beyond agent-initiated and direct contact events.
Historians of science have pointed to essentialist beliefs about species as major impediments to ... more Historians of science have pointed to essentialist beliefs about species as major impediments to the discovery of natural selection. The present study investigated whether such beliefs are impediments to learning this concept as well. Participants (43 children aged 4–9 and 34 adults) were asked to judge the variability of various behavioral and anatomical properties across different members of the same species. Adults who accepted within-species variation—both actual and potential—were significantly more likely to demonstrate a selection-based understanding of evolution than adults who denied within-species variation. The latter demonstrated an alternative, incorrect understanding of evolution and produced response patterns that were both quantitatively and qualitatively similar to those produced by preschool-aged children. Overall, it is argued that psychological essentialism, although a useful bias for drawing species-wide inductions, leads individuals to devalue within-species variation and, consequently, to fail to understand natural selection.
Previous research (e.g., Gelman & Markman, 1986; Gopnik & Sobel, 2000) suggests that children can... more Previous research (e.g., Gelman & Markman, 1986; Gopnik & Sobel, 2000) suggests that children can use category labels to make inductive inferences about non-obvious causal properties of objects. However, such inductive generalizations can fail to predict objects' causal properties when A) the property being projected varies within the category; B) the category is arbitrary (e.g., things smaller than a bread box), or C) the property being projected is due to an exogenous intervention rather than intrinsic to the object kind. In four studies, we show that preschoolers (mean: 48 months; range: 42-57 months) are sensitive to these constraints on induction and selectively engage in exploration when evidence about objects' causal properties conflicts with inductive generalizations from the objects' kind to their causal powers. This suggests that the exploratory actions children generate in free play could support causal learning.
We propose a rational analysis of children's false belief reasoning. Our analysis realizes a cont... more We propose a rational analysis of children's false belief reasoning. Our analysis realizes a continuous, evidencedriven transition between two causal Bayesian models of false belief. Both models support prediction and explanation; however, one model is less complex while the other has greater explanatory resources. Because of this explanatory asymmetry, unexpected outcomes weigh more heavily against the simpler model. We test this account empirically by showing children the standard outcome of the false belief task and a novel "psychic" outcome. As expected, we find children whose explanations and predictions are consistent with each model, and an interaction between prediction and explanation. Critically, we find unexpected outcomes only induce children to move from predictions consistent with the simpler model to those consistent with the more complex one, never the reverse.
Researchers, educators, and parents have long believed that children learn cause and effect relat... more Researchers, educators, and parents have long believed that children learn cause and effect relationships through exploratory play. However, previous research suggests that children are poor at designing informative experiments; children fail to control relevant variables and tend to alter multiple variables simultaneously. Thus, little is known about how children's spontaneous exploration might support accurate causal inferences. Here we suggest that children's exploratory play is affected by the quality of the evidence they observe. Using a novel free-play paradigm, we show that preschoolers (mean age: 57 months) distinguish confounded and unconfounded evidence, preferentially explore causally confounded (but not matched unconfounded) toys rather than novel toys, and spontaneously disambiguate confounded variables in the course of free play.
Causal learning requires integrating constraints provided by domain-specific theories with domain... more Causal learning requires integrating constraints provided by domain-specific theories with domain-general statistical learning. In order to investigate the interaction between these factors, preschoolers were presented with stories pitting their existing theories against statistical evidence. Each child heard two stories in which two candidate causes co-occurred with an effect. Evidence was presented in the form: AB E, AC E, AD E, etc. In one story, all variables came from the same domain; in the other, the recurring candidate cause, A, came from a different domain (A was a psychological cause of a biological effect). After receiving this statistical evidence, children were asked to identify the cause of the effect on a new trial. Consistent with the predictions of a Bayesian model, all children were more likely to identify A as the cause within domains than across domains. While three-and-half-year-olds learned only from the withindomain evidence, four-and five-year-olds learned from the cross-domain evidence and were able to transfer their new expectations about psychosomatic causality to a novel task.
Three studies investigated whether young children make accurate causal inferences on the basis of... more Three studies investigated whether young children make accurate causal inferences on the basis of patterns of variation and covariation. Children were presented with a new causal relation by means of a machine called the "blicket detector." Some objects, but not others, made the machine light up and play music. In the first 2 experiments, children were told that "blickets make the machine go" and were then asked to identify which objects were "blickets." Two-, 3-, and 4-year-old children were shown various patterns of variation and covariation between two different objects and the activation of the machine. All 3 age groups took this information into account in their causal judgments about which objects were blickets. In a 3rd experiment, 3-and 4-year-old children used the information when they were asked to make the machine stop. These results are related to Bayes-net causal graphical models of causal learning.
The false belief task commonly used in the study of theory of mind (ToM) requires participants to... more The false belief task commonly used in the study of theory of mind (ToM) requires participants to select among competing responses and inhibit prepotent responses, giving rise to three possibilities: (1) the false belief tasks might require only executive function abilities and there may be no domain-specific component; (2) executive control might be necessary for the emergence of ToM in development but play no role in adult mental state inferences; and (3) executive control and domain-specific ToM abilities might both be implicated. We used fMRI in healthy adults to dissociate these possibilities. We found that non-overlapping brain regions were implicated selectively in response selection and belief attribution, that belief attribution tasks recruit brain regions associated with response selection as much as wellmatched control tasks, and that regions associated with ToM (e.g., the right temporo-parietal junction) were implicated only in the belief attribution tasks. These results suggest that both domain-general and domain-specific cognitive resources are involved in adult ToM.
The conditional intervention principle is a formal principle that relates patterns of interventio... more The conditional intervention principle is a formal principle that relates patterns of interventions and outcomes to causal structure. It is a central assumption of the causal Bayes net formalism. Four experiments suggest that preschoolers can use the conditional intervention principle both to learn complex causal structure from patterns of evidence and to predict patterns of evidence from knowledge of causal structure. Other theories of causal learning do not account for these results.
Five studies investigated (a) children's ability to use the dependent and independent probabiliti... more Five studies investigated (a) children's ability to use the dependent and independent probabilities of events to make causal inferences and (b) the interaction between such inferences and domain-specific knowledge. In Experiment 1, preschoolers used patterns of dependence and independence to make accurate causal inferences in the domains of biology and psychology. Experiment 2 replicated the results in the domain of biology with a more complex pattern of conditional dependencies. In Experiment 3, children used evidence about patterns of dependence and independence to craft novel interventions across domains. In Experiments 4 and 5, children's sensitivity to patterns of dependence was pitted against their domain-specific knowledge.
The authors outline a cognitive and computational account of causal learning in children. They pr... more The authors outline a cognitive and computational account of causal learning in children. They propose that children use specialized cognitive systems that allow them to recover an accurate "causal map" of the world: an abstract, coherent, learned representation of the causal relations among events. This kind of knowledge can be perspicuously understood in terms of the formalism of directed graphical causal models, or Bayes nets. Children's causal learning and inference may involve computations similar to those for learning causal Bayes nets and for predicting with them. Experimental results suggest that 2to 4-year-old children construct new causal maps and that their learning is consistent with the Bayes net formalism.
In addition to effects on metabolism and appetite, leptin is a reproductive hormone produced and ... more In addition to effects on metabolism and appetite, leptin is a reproductive hormone produced and secreted by the placenta of many, but not all mammalian species. In mice, in which the placenta does not secrete leptin, exogenously added leptin stimulates invasiveness of early (but not late)-gestation trophoblast cells. We report a similar phenomenon occurs in Myotis lucifugus (little brown myotis), a species in which the placenta synthesizes and secretes leptin. Immunoneutralization of endogenously secreted leptin from cultured M. lucifugus trophoblast cells inhibited the ability of these cells to invade a matrigel matrix. The effect was not due to an inhibitory effect of the antibody on cell proliferation, nor was it a non-specific effect of antibody administration. Cell invasion was significantly reduced in untreated cells obtained from late-gestation placentas, and the antibody had no effect at that time. This occurred despite continued expression throughout gestation of the long (OBRb) and short (OBRa) isoforms of leptin receptor mRNA. This study suggests that an important function of leptin during pregnancy is an effect on trophoblast cell invasiveness, at a time when the placenta is becoming established. That this occurs in two phylogenetically unrelated and distant species, regardless of whether the placenta is a source of secreted leptin, suggests that this is a highly conserved reproductive action of leptin.
The ability to make inductive inferences from sparse data is a critical aspect of human learning.... more The ability to make inductive inferences from sparse data is a critical aspect of human learning. However, the properties observed in a sample of evidence depend not only on the true extension of those properties but also on the process by which evidence is sampled. Because neither the property extension nor the sampling process is directly observable, the learner's ability to make accurate generalizations depends on what is known or can be inferred about both variables. In particular, different inferences are licensed if samples are drawn randomly from the whole population (weak sampling) than if they are drawn only from the property's extension (strong sampling). Given a few positive examples of a concept, only strong sampling supports flexible inferences about how far to generalize as a function of the size and composition of the sample. Here we present a Bayesian model of the joint dependence between observed evidence, the sampling process, and the property extension and test the model behaviorally with human infants (mean age: 15 months). Across five experiments, we show that in the absence of behavioral cues to the sampling process, infants make inferences consistent with the use of strong sampling; given explicit cues to weak or strong sampling, they constrain their inferences accordingly. Finally, consistent with quantitative predictions of the model, we provide suggestive evidence that infants' inferences are graded with respect to the strength of the evidence they observe.
Previous work has demonstrated the importance of both naïve theories and statistical evidence to ... more Previous work has demonstrated the importance of both naïve theories and statistical evidence to children's causal reasoning. In particular, four-year-olds can use statistical evidence to update their beliefs. However, the story is more complex for three-year-olds. Although three-and-a-half-yearolds perform as well as four-year-olds when statistical evidence is theory-neutral, several studies suggest that they do not learn from statistical evidence when a statistically likely cause is inconsistent with their prior beliefs (e.g., . There are at least two possible explanations for younger children's failure to use statistical data to update their beliefs: one (the Information Processing account) suggests that younger children have a fragile ability to reason about statistical evidence; the other (a Prior Knowledge account) suggests that in some domains, younger children have stronger prior beliefs and thus require more evidence before belief revision is rational. To distinguish these accounts, we conducted a two-week training study with three-and-a-halfyear-olds. Children participated in an Information Processing Training condition, a Prior Belief Training condition, or a Control condition.
Given minimal evidence about novel objects, children might learn only relationships among the spe... more Given minimal evidence about novel objects, children might learn only relationships among the specific entities, or they might make a more abstract inference, positing classes of entities and the relations that hold among those classes. Here we show that preschoolers (mean: 57 months) can use sparse data about perceptually unique objects to infer abstract physical causal laws. These newly inferred abstract laws were robust to potentially anomalous evidence; in the face of apparent counter-evidence, children (correctly) posited the existence of an unobserved object rather than revise the abstract laws. This suggests that children's ability to learn robust, abstract principles does not depend on extensive prior experience but can occur rapidly, on-line, and in tandem with inferences about specific relations.
Adults' causal representations integrate information about predictive relations and the possibili... more Adults' causal representations integrate information about predictive relations and the possibility of effective intervention; if one event reliably predicts another, adults can represent the possibility that acting to bring about the first event might generate the second. Here we show that although toddlers (mean age: 24 months) readily learn predictive relationships between physically connected events, they do not spontaneously initiate one event to try to generate the second (although older children, mean age: 47 months, do; Experiments 1 and 2). Toddlers succeed only when the events are initiated by a dispositional agent (Experiment 3), when the events involve direct contact between objects (Experiment 4), or when the events are described using causal language (Experiment 5). This suggests that causal language may help children extend their initial causal representations beyond agent-initiated and direct contact events.
Historians of science have pointed to essentialist beliefs about species as major impediments to ... more Historians of science have pointed to essentialist beliefs about species as major impediments to the discovery of natural selection. The present study investigated whether such beliefs are impediments to learning this concept as well. Participants (43 children aged 4–9 and 34 adults) were asked to judge the variability of various behavioral and anatomical properties across different members of the same species. Adults who accepted within-species variation—both actual and potential—were significantly more likely to demonstrate a selection-based understanding of evolution than adults who denied within-species variation. The latter demonstrated an alternative, incorrect understanding of evolution and produced response patterns that were both quantitatively and qualitatively similar to those produced by preschool-aged children. Overall, it is argued that psychological essentialism, although a useful bias for drawing species-wide inductions, leads individuals to devalue within-species variation and, consequently, to fail to understand natural selection.
Previous research (e.g., Gelman & Markman, 1986; Gopnik & Sobel, 2000) suggests that children can... more Previous research (e.g., Gelman & Markman, 1986; Gopnik & Sobel, 2000) suggests that children can use category labels to make inductive inferences about non-obvious causal properties of objects. However, such inductive generalizations can fail to predict objects' causal properties when A) the property being projected varies within the category; B) the category is arbitrary (e.g., things smaller than a bread box), or C) the property being projected is due to an exogenous intervention rather than intrinsic to the object kind. In four studies, we show that preschoolers (mean: 48 months; range: 42-57 months) are sensitive to these constraints on induction and selectively engage in exploration when evidence about objects' causal properties conflicts with inductive generalizations from the objects' kind to their causal powers. This suggests that the exploratory actions children generate in free play could support causal learning.
We propose a rational analysis of children's false belief reasoning. Our analysis realizes a cont... more We propose a rational analysis of children's false belief reasoning. Our analysis realizes a continuous, evidencedriven transition between two causal Bayesian models of false belief. Both models support prediction and explanation; however, one model is less complex while the other has greater explanatory resources. Because of this explanatory asymmetry, unexpected outcomes weigh more heavily against the simpler model. We test this account empirically by showing children the standard outcome of the false belief task and a novel "psychic" outcome. As expected, we find children whose explanations and predictions are consistent with each model, and an interaction between prediction and explanation. Critically, we find unexpected outcomes only induce children to move from predictions consistent with the simpler model to those consistent with the more complex one, never the reverse.
Researchers, educators, and parents have long believed that children learn cause and effect relat... more Researchers, educators, and parents have long believed that children learn cause and effect relationships through exploratory play. However, previous research suggests that children are poor at designing informative experiments; children fail to control relevant variables and tend to alter multiple variables simultaneously. Thus, little is known about how children's spontaneous exploration might support accurate causal inferences. Here we suggest that children's exploratory play is affected by the quality of the evidence they observe. Using a novel free-play paradigm, we show that preschoolers (mean age: 57 months) distinguish confounded and unconfounded evidence, preferentially explore causally confounded (but not matched unconfounded) toys rather than novel toys, and spontaneously disambiguate confounded variables in the course of free play.
Causal learning requires integrating constraints provided by domain-specific theories with domain... more Causal learning requires integrating constraints provided by domain-specific theories with domain-general statistical learning. In order to investigate the interaction between these factors, preschoolers were presented with stories pitting their existing theories against statistical evidence. Each child heard two stories in which two candidate causes co-occurred with an effect. Evidence was presented in the form: AB E, AC E, AD E, etc. In one story, all variables came from the same domain; in the other, the recurring candidate cause, A, came from a different domain (A was a psychological cause of a biological effect). After receiving this statistical evidence, children were asked to identify the cause of the effect on a new trial. Consistent with the predictions of a Bayesian model, all children were more likely to identify A as the cause within domains than across domains. While three-and-half-year-olds learned only from the withindomain evidence, four-and five-year-olds learned from the cross-domain evidence and were able to transfer their new expectations about psychosomatic causality to a novel task.
Three studies investigated whether young children make accurate causal inferences on the basis of... more Three studies investigated whether young children make accurate causal inferences on the basis of patterns of variation and covariation. Children were presented with a new causal relation by means of a machine called the "blicket detector." Some objects, but not others, made the machine light up and play music. In the first 2 experiments, children were told that "blickets make the machine go" and were then asked to identify which objects were "blickets." Two-, 3-, and 4-year-old children were shown various patterns of variation and covariation between two different objects and the activation of the machine. All 3 age groups took this information into account in their causal judgments about which objects were blickets. In a 3rd experiment, 3-and 4-year-old children used the information when they were asked to make the machine stop. These results are related to Bayes-net causal graphical models of causal learning.
The false belief task commonly used in the study of theory of mind (ToM) requires participants to... more The false belief task commonly used in the study of theory of mind (ToM) requires participants to select among competing responses and inhibit prepotent responses, giving rise to three possibilities: (1) the false belief tasks might require only executive function abilities and there may be no domain-specific component; (2) executive control might be necessary for the emergence of ToM in development but play no role in adult mental state inferences; and (3) executive control and domain-specific ToM abilities might both be implicated. We used fMRI in healthy adults to dissociate these possibilities. We found that non-overlapping brain regions were implicated selectively in response selection and belief attribution, that belief attribution tasks recruit brain regions associated with response selection as much as wellmatched control tasks, and that regions associated with ToM (e.g., the right temporo-parietal junction) were implicated only in the belief attribution tasks. These results suggest that both domain-general and domain-specific cognitive resources are involved in adult ToM.
The conditional intervention principle is a formal principle that relates patterns of interventio... more The conditional intervention principle is a formal principle that relates patterns of interventions and outcomes to causal structure. It is a central assumption of the causal Bayes net formalism. Four experiments suggest that preschoolers can use the conditional intervention principle both to learn complex causal structure from patterns of evidence and to predict patterns of evidence from knowledge of causal structure. Other theories of causal learning do not account for these results.
Five studies investigated (a) children's ability to use the dependent and independent probabiliti... more Five studies investigated (a) children's ability to use the dependent and independent probabilities of events to make causal inferences and (b) the interaction between such inferences and domain-specific knowledge. In Experiment 1, preschoolers used patterns of dependence and independence to make accurate causal inferences in the domains of biology and psychology. Experiment 2 replicated the results in the domain of biology with a more complex pattern of conditional dependencies. In Experiment 3, children used evidence about patterns of dependence and independence to craft novel interventions across domains. In Experiments 4 and 5, children's sensitivity to patterns of dependence was pitted against their domain-specific knowledge.
The authors outline a cognitive and computational account of causal learning in children. They pr... more The authors outline a cognitive and computational account of causal learning in children. They propose that children use specialized cognitive systems that allow them to recover an accurate "causal map" of the world: an abstract, coherent, learned representation of the causal relations among events. This kind of knowledge can be perspicuously understood in terms of the formalism of directed graphical causal models, or Bayes nets. Children's causal learning and inference may involve computations similar to those for learning causal Bayes nets and for predicting with them. Experimental results suggest that 2to 4-year-old children construct new causal maps and that their learning is consistent with the Bayes net formalism.
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Papers by Laura Schulz