Infants' and toddlers' reasoning about others: Connections to prosocial development and language The Harvard community has made this article openly available. Please share how this access benefits you. Your story matters Citation Hobbs, Kathryn Virginia. 2014. Infants' and toddlers' reasoning about others: Connections to prosocial development and language. Doctoral dissertation, Harvard University. Citable link http://nrs.harvard.edu/urn-3:HUL.InstRepos:13065030 Terms of Use This article was downloaded from Harvard University’s DASH repository, and is made available under the terms and conditions applicable to Other Posted Material, as set forth at http:// nrs.harvard.edu/urn-3:HUL.InstRepos:dash.current.terms-of- use#LAA Infants’ and toddlers’ reasoning about others: Connections to prosocial development and language A dissertation presented by Kathryn Virginia Hobbs to The Department of Psychology in partial fulfillment of the requirements for the degree of Doctor of Philosophy in the subject of Psychology Harvard University Cambridge, Massachusetts September 2014 © 2014 Kathryn Virginia Hobbs All rights reserved. ! Dissertation Advisor: Professor Elizabeth Spelke Kathryn Virginia Hobbs Infants' and toddlers' reasoning about others: Connections to prosocial development and language Abstract Often overlooked in the study of theory of mind (ToM) development, the understanding of motivational states, such as goals and desires, is both important in its own right and also a likely precursor to more advanced social and cognitive skills. This dissertation explored infants’ and toddlers’ reasoning about agents’ motivational states, linking those representations to the domains of language and prosocial development. Parts I and II of the dissertation asked about toddlers’ abilities to use representations of others’ motivational states to guide helping behaviors. Part I used a spontaneous helping paradigm with two goal objects, one previously liked and the other disliked. Three- but not 2-year-olds helped appropriately by giving an actor her desired object, reflecting prosocial concern for others’ specific desires at age 3. Part II probed the understanding of goals and helping of 14- and 24-month-olds. After establishing that toddlers encode simple reaching actions as goal-directed, a series of 4 experiments using an object-giving paradigm investigated toddlers’ abilities to use goal representations to guide helping. The results indicate that 24- but not 14-month-olds used representations of prior goals to inform their helping behaviors; 14-month-olds were capable of using only current goals to guide helping. Part III of the dissertation asked whether there is continuity in the developmental relationship between language and ToM by investigating links between toddlers’ ! """! understanding of motivational states and their vocabulary size. Experiment 1 found no correlation between the vocabulary size of typically hearing toddlers and their performance on tasks measuring motivational state understanding. Experiment 2 compared the same motivational state understanding of typically hearing toddlers and deaf toddlers with smaller vocabularies, finding no differences in performance between groups. The results of these experiments indicate that the link between language and false belief that is present at age 4 does not extend to motivational state reasoning in the toddler years. Together the findings of this dissertation highlight important limits and boundary conditions on young children’s reasoning about motivational states. Further research is needed into the developmental trajectory and mechanisms of theory of mind reasoning. ! "#! Table of Contents Acknowledgements……………………………………………………………………….vi Introduction………………………………………………………………………………..1 Part I—What do you want? Three-year-olds, but not 2-year-olds help with specific desires…………………………………………………………………………....23 Part II—Goal attributions and instrumental helping at 14 and 24 months of age……….43 Part III—Relations between motivational state reasoning and vocabulary size in toddlerhood………………………………………………………………………86 Conclusion……………………………………………………………………………...127 References………………………………………………………………………………134 ! #! Acknowledgements There are many individuals to whom I owe a great deal of gratitude, and it is a pleasure to acknowledge their support here. First, I thank my committee members and advisors, each of who has made a unique contribution to my development as a scholar and a person. I credit Elizabeth Spelke, as my first and principal advisor, with getting me excited about exploring helping in infancy. As anyone will tell you, Liz’s enthusiasm for research is infectious and inspiring, and I am very grateful to have had the opportunity to learn from Liz. I thank Felix Warneken for being a fantastic mentor and collaborator, and a great role model of perseverance and dedication. Thank you to Susan Carey, whose mentorship and support were essential to my survival in graduate school. Susan’s unflagging commitment to her students is impressive, and she is of course a fantastic person to think and work with. I am very grateful to Jennie Pyers as a mentor, confidante and collaborator. Working with Jennie has been one of the most valuable experiences of my graduate school career. I am also deeply grateful to my “academic parents,” Jill and Peter de Villiers, who set me on the path to graduate school. I was spoiled working as their Research Assistant; Jill would ask me to “come up and think” with her and Peter made fresh vegan baked goods for lab tea every week. Jill and Peter represent the model of intellectual rigor paired with genuine human interest. It is an honor to be part of their lineage. I am grateful for support from various funding sources, including a Graduate Research Fellowship from the National Science Foundation, a conference travel award from Harvard’s Graduate Student Council, conference travel awards and two Restricted Funds large grant awards from the Psychology Department at Harvard. ! #"! I am indebted to all of the people who make the Lab for Developmental Studies an amazing intellectual and social community. This includes all the members of the Carey, Snedeker, Spelke & Warneken labs who have provided invaluable feedback and camaraderie over the years. A huge thanks goes to the lab managers who have tolerated me over the years: Konika Banerjee, Natalie Benjamin, Conisha Cooper, Rebecca Distefano, Danielle Hinchey, McCaila Ingold-Smith, Yeshim Iqbal, Rachel Katz, Lauren Kleutch, Kerrie Pieloch, Ellyn Schmidt and Rosemary Zeimnik. My research could not have gotten off the ground without the tireless efforts of many undergraduate research assistants. It has also been a privilege to work collaboratively with former undergraduate thesis student Westley Resendes, without whose efforts Part III of this dissertation would not have been possible. Outside of LDS I am very grateful for the support of students and staff at the Center of the Developing Child at Harvard, where the Student Seminar Series, Doctoral Working Group and Early Childhood Forum helped me stay grounded in my desire to leverage research in cognitive development to improve the lives of children and families. I extend a huge thanks to my friends and family for putting up with me during graduate school, mostly by enduring long absences on my part and in giving me a world away from cognitive developmental when I needed it. I thank my parents, Jane and Bob Hobbs, for supporting me and encouraging me in my lifelong journey of learning, but more than anything for fostering my sense of self and self-worth as separate from my accomplishments. Thanks, Mom and Dad. Lastly, I thank my wife, Anna Paskausky, who has walked with me every step of the way. Thank you, Ap, for letting me be real all the time, believing in me and ! #""! reminding me of my true self when I forgot. I promise to never let you live down falling asleep during my practice talk for my first LDS Seminar. ! #"""! Introduction Overview As humans we constantly and automatically attribute mental states to others to explain their behavior. Without a theory of mind (ToM), we would be lost in interpreting jokes, movies, literature and our spouses. The study of ToM is important both theoretically, in terms of delineating what makes us uniquely human, and practically, in its implications for social and educational competency. Within developmental psychology, research on ToM has been a dominant topic of inquiry for the past several decades (Premack & Woodruff, 1978; Wimmer & Perner, 1983). Researchers have sketched a picture of ToM development that began with gaze following, engagement in joint attention, and goal understanding in the first year of life, followed by an understanding of others’ desires, knowledge states and true beliefs in the second and third (Poulin-Dubois, Brooker & Chow, 2009). For many years, the greatest challenge to ToM researchers was how to explain the dramatic shift around the fourth birthday in children’s ability to reason about false beliefs (Wellman, Cross & Watson, 2001). With the recent barrage of findings that even infants reason about agents’ actions in terms of their mental states including false beliefs (for a review see Baillargeon et al., 2014), attention has shifted to the infant and toddler years in an attempt to characterize the earliest ToM competencies and reconcile findings of infants’ precocious abilities with toddlers’ shortcomings in explicit false belief reasoning. The questions that loom largest are those that apply to