Sarcasm and Advanced Theory of Mind Understanding in Children and Adults With Prelingual Deafness Karin O’Reilly and Candida C. Peterson University of Queensland Henry M. Wellman University of Michigan Two studies addressed key theoretical debates in theory of mind (ToM) development by comparing (a) deaf native signers (n = 18), (b) deaf late signers (n = 59), and (c) age-matched hearing persons (n = 74) in childhood (Study 1: n = 81) and adulthood (Study 2: n = 70) on tests of first- and second-order false belief and conversational sarcasm. Results showed ToM development to be a life span phenomenon for deaf and hearing people alike. Native and late signers were outperformed by hearing peers on advanced ToM in childhood (M = 9 years), but in adulthood (M = 40 years), native signers had caught up, whereas late signers had not. Findings highlight the extended importance of conversational interac- tion for ToM growth. Keywords: deafness, theory of mind, sarcasm understanding, second-order false belief, life span social cognition Theory of mind (ToM)—the explicit understanding of how human behavior is governed by mental states (beliefs, memories, intentions, and so on)—is assessed prototypically with first-order false belief tests requiring predictions about the thoughts or be- havior of protagonists whose beliefs are at odds with reality. Most 3-year-olds fail these tests, but success is so routine by typically developing, hearing children ages 5 years and over as to suggest that the understanding of others’ minds undergoes a “genuine conceptual change during the preschool period” (Wellman, Cross, & Watson, 2001, p. 655). However, the picture is complicated and less understood for children with certain disabilities—for example, for severely or profoundly deaf children of normal intelligence who are often delayed in mastering ToM when they grow up in hearing homes where no one uses sign language with native-language proficiency. Indeed, studies of more than 700 severely or profoundly deaf children worldwide (encompassing a variety of languages and approaches to deaf education) show consistently high rates of ToM failure throughout primary school and into adolescence by those with hearing parents (see Peterson, 2004, 2009; Siegal & Peterson, 2008, for reviews). Yet an intriguing minority of severely and profoundly deaf children escape ToM delays. These are the natively signing deaf children who have signing deaf parent(s). When a deaf parent signs fluently, the child grows up having ordinary conversational expe- riences from birth—albeit in sign language rather than speech. Extensive research reveals markedly superior performance by young deaf native signers compared with matched groups of deaf children from hearing families (late signers) on false belief tests (e.g., Courtin & Melot, 1998; Meristo et al., 2007; Peterson & Siegal, 1999; Schick, deVilliers, deVilliers, & Hoffmeister, 2007) and on other standard measures of preschool ToM understanding (e.g., Peterson, Wellman, & Liu, 2005). Native signers’ perfor- mance is similar to that of hearing children the same age, whereas late signers are often as delayed as age-and IQ-matched children with autism (e.g., Peterson, 2002; Peterson & Siegal, 2000). Thus, it is not deafness per se but rather the conjunction of hearing loss with upbringing in a hearing family that underpins poor performance on standard false belief tests of ToM. Despite extensive and conscientious efforts to learn to sign, hearing parents very rarely become fully proficient, so few can communicate effectively with their deaf offspring about topics like thoughts and other mental states that cannot readily be mimed, seen, or pointed at (e.g., Moeller & Schick, 2006; Vaccari & Marschark, 1997). Notably, false belief performance by deaf children of hearing parents correlates with the number of signs for cognitive verbs that their parents know and use (Moeller & Schick, 2006). Further, for native signers, richness of the early family conversational envi- ronment directly explains superiority over late signers on false belief tests, even after controlling statistically for other potential contributors like vocabulary size, executive functioning, and syn- tactic language skill (e.g., Schick et al., 2007; Woolfe, Want, & Siegal, 2002). Commensurate with their delayed and limited abilities to par- ticipate freely in family conversations as preschoolers, many orally educated deaf children, including those with cochlear implants, lag This article was published Online First May 5, 2014. Karin O’Reilly and Candida C. Peterson, School of Psychology, Uni- versity of Queensland; Henry M. Wellman, Department of Psychology, University of Michigan. With sincere gratitude, we acknowledge the fine cooperation of all the adults who took part and that of the children, their parents, and their teachers. This research, partially supported by National Institutes of Health MERIT Award HD022149 (to the third author), was conducted during the first author’s enrollment as a doctoral student in psychology at the Uni- versity of Queensland under the second author’s supervision. Correspondence concerning this article should be addressed to Candida C. Peterson, School of Psychology, University of Queensland, Brisbane, Queensland 4072, Australia. E-mail: candi@psy.uq.edu.au This document is copyrighted by the American Psychological Association or one of its allied publishers. This article is intended solely for the personal use of the individual user and is not to be disseminated broadly. Developmental Psychology © 2014 American Psychological Association 2014, Vol. 50, No. 7, 1862–1877 0012-1649/14/$12.00 http://dx.doi.org/10.1037/a0036654 1862