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Understanding Other MindsPerspectives from developmental social neuroscience$

Simon Baron-Cohen, Michael Lombardo, and Helen Tager-Flusberg

Print publication date: 2013

Print ISBN-13: 9780199692972

Published to Oxford Scholarship Online: September 2013

DOI: 10.1093/acprof:oso/9780199692972.001.0001

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Theory of mind in deaf children

Theory of mind in deaf children

Illuminating the relative roles of language and executive functioning in the development of social cognition

Chapter:
(p.344) (p.345) Chapter 19 Theory of mind in deaf children
Source:
Understanding Other Minds
Author(s):

Jennie Pyers

Peter A. de Villiers

Publisher:
Oxford University Press
DOI:10.1093/acprof:oso/9780199692972.003.0019

Abstract and Keywords

While executive function and language both support false-belief understanding in typically developing children, our review of the research with deaf children shows that in this population, language plays a stronger role than executive function in developing an explicit understanding of false beliefs. In addressing this discrepancy, we discuss the methodological challenges of conducting research with deaf children and explore deaf children's development of other aspects of theory of mind, including intentions and desires, sources-of-knowledge, implicit false-belief understanding, and joint attention. Taken together, the current evidence supports the importance of early language exposure and children’s own language acquisition in building a mature theory of mind.

Keywords:   Deafness, theory of mind, false belief, deception, language, inhibitory control, executive function

In the mid-1990s several independent programs of research and theorizing proposed that studies of deaf children could illuminate the role of language in children’s theory of mind (ToM) or more broadly in their social cognitive development. For example, in a theoretical paper about the relationship between language and thought, Jackendoff (1996) argued that language was necessary for making explicit judgments about the truth and falsity of propositions. In a footnote he noted that a colleague had recognized that an implication of his theory was that language-delayed deaf children would have difficulty with false-belief (FB) tasks. Just at that time, two independent research groups confirmed that hypothesis: one with late signing deaf children (Peterson & Siegal, 1995) and the other with orally-taught deaf children (Gale, de Villiers, de Villiers, & Pyers, 1996). Indeed, deaf children with hearing parents provide a strong test of the hypothesis that language plays a causal role in ToM development because these children experience varying degrees of language delay, but typically have a normal IQ and active sociability.

In this chapter we first discuss some crucial methodological challenges in studying ToM development in deaf children. In the light of these methodological issues, we review the most comprehensive studies of deaf children’s explicit FB reasoning and how language and executive function (EF) ability does and does not affect this development. Since the initial ground-breaking research, the picture of deaf children’s ToM has gotten considerably more complex. The resulting picture confirms other arguments that many different components constitute a fully articulated “theory of mind” (e.g. Wellman & Liu, 2004), and each of these components may be differentially affected by language acquisition and/or executive functioning. We will show that some social cognitive understandings, such as those embodied in deceptive games with low verbal requirements, do not appear to be delayed by language-impairment resulting from deafness and are predicted by inhibitory control (an aspect of EF) not language skills. Others, such as reasoning about states of knowledge and ignorance and explicit judgments about false beliefs are considerably delayed and closely predicted by language, but not by deaf children’s EF.

Methodological issues

The existing literature points to significant limitations in FB reasoning in deaf children, but different studies report widely variable ages at which deaf children of hearing parents succeed on either high-verbal or low-verbal measures of FB understanding. Some of this variability may be (p.346) attributed to the diversity of the deaf samples studied, and some may be attributed to methodological differences in the assessment of deaf children.

Key to what makes deaf children an ideal population in which to investigate the relative contributions of language and EF to ToM development is the diversity of deaf children’s language experience. Typically two distinct populations of deaf children are included in studies of ToM. Deaf children born to deaf parents (DoD) function as a control population because, despite their deafness, they have native exposure to an accessible first language, a natural sign language. Thus, they have normal language acquisition, albeit in a different modality from typically-hearing (TH) children. On the other hand, deaf children born to hearing parents (DoH) have greater variability in their language experience: some acquire a natural sign language, some learn only a manually coded version of the spoken language of their community (e.g. signed English), and others never learn to sign and are exposed only to oral language. Whatever their language experience, DoH children typically display some degree of language delay without any corresponding congenital cognitive deficit (Marschark, 1993). While the language delay makes DoH children the ideal population in which to test the effects of language on ToM, the diversity within this group can yield widely different levels of performance. As such, studies that provide the strongest information about the effects of language on ToM in deaf children include detailed information about the children’s language experience as well as measures of their ability in their preferred language, signed or spoken.

Background variables, beyond language experience, can also impact children’s performance. Relative to the TH children who are commonly recruited from university-affiliated preschools, deaf children in the United States come from more diverse socio-economic backgrounds (SES) and may have other physical and cognitive challenges. Several of these background variables that might impact children’s ToM performance are summarized in Table 19.1. Ideally, researchers should include large samples of deaf children in their studies to minimize the effect of these other variables. However, with only 0.64% of children in the United States diagnosed as hard-of-hearing or deaf (Mitchell, 2006), recruiting large samples of deaf children remains difficult and expensive. Alternatively, researchers could address the variability in deaf samples either by finding a TH sample that closely matches the deaf sample on SES and on general cognitive ability, or by statistically controlling for all of the background variables, a difficult task with the usual small sample sizes.

Approaches to deaf education also shape the characteristics of the deaf population to which researchers have the easiest access. The current educational practice in the United States and in many other Western countries is to work toward deaf children’s full integration into educational programs for typically-developing children. As soon as deaf children develop the social, cognitive, and linguistic foundations deemed necessary to succeed, they are often placed in mainstream schools with TH children, and they learn with the support of sign language interpreters and/or additional amplification services. Deaf children can enter the mainstream in some cases as early as preschool or as late as high school. Some deaf children never transfer into integrated programs for a variety of reasons including parental choice or not having acquired the foundational skills that the program considers necessary for educational success. The practice of transferring deaf children to integrated programs means that many older deaf children with age-appropriate language and cognitive abilities are no longer enrolled in programs that educate only deaf children. Thus studies that target only deaf children enrolled in special schools or programs for the deaf may not be representative of the most successful deaf children. This limitation is greater for studies that include children beyond the preschool and kindergarten years; deaf children start to move into the mainstream during the early elementary years, leaving behind classrooms where children who (p.347)

Table 19.1 Background variables that must be accounted for to best interpret data from studies of deaf children

SES

SES affects FB performance in typically developing children, with children from higher SES families outperforming children from less privileged backgrounds (Cicchetti, Rogosch, Maughan, Toth, & Bruce, 2003; Shatz, Diesendruck, Martinez-Beck, & Akar, 2003). When deaf and hearing children are matched for SES and non-verbal IQ, native signers perform equivalently or even better than TH children on FB tasks, and the reported difference between DoH and DoD children is much smaller (Courtin, 2000; Schick, de Villiers, de Villiers, & Hoffmeister, 2007).

Non-verbal intelligence

The inclusion of measures of non-verbal intelligence such as spatial working memory ensures that the children in the sample have a normal intellectual level and reduces the likelihood that any limitations observed in ToM performance are due to limitations in general intellectual ability.

Physical or cognitive impairments aside from deafness

Deafness sometimes is co-morbid with other physical or intellectual disabilities that may affect performance on FB tasks independently of language (Marschark, 1993). Such information gathered from the school helps guide researchers as to whether it is necessary to exclude these children from the final analyses.

General language ability

For deaf children exposed only to a spoken language, measures of spoken language development that have been validated with deaf children are appropriate. In the United States, such measures include the CELF and the Rhode Island Test of Language Structure (Engen & Engen, 1983). The assessment of sign language ability is much more difficult without standardized measures. Several researchers have developed their own language measures to compare sign language development in DoD and DoH children (e.g. Schick et al., 2007), but these measures do not always allow for cross-linguistic comparisons of signed and spoken language acquisition. Signed translations of spoken language measures are not valid measures of natural sign language acquisition.

Age of first language exposure/age of amplification

Age of first exposure to language impacts language ability (Mayberry & Lock, 2003). For non-native signing children, age of first language exposure is typically the age at which they entered a signing program; for oral deaf children it is usually the age when they receive their first amplification to enhance their auditory access to spoken language. In the United States, all children who are identified with a hearing-loss at birth receive state-supported early intervention that provides both auditory and language intervention. However, some families first choose an oral-only methodology, but later introduce their child to a sign language when the child struggles with acquiring a spoken language.

Language exposure in the home

For signing children, the degree to which hearing parents learn a sign language varies. Some parents become more fluent than others (Moeller & Schick, 2006; Vaccari & Marschark, 1997). In addition, some hearing parents of deaf children speak more than one spoken language in the home, reducing the amount of English heard by orally taught deaf children.

(p.348) have other needs beyond deafness outnumber children who otherwise exhibit typical cognitive, physical, and social development.

Beyond careful consideration of the variability in deaf children’s backgrounds, researchers’ testing methods can impact the children’s performance. First, most deaf children primarily acquire linguistic information through the visual channel by viewing signs or reading lips. Some traditional FB measures engage TH children’s ability to monitor visual and auditory information simultaneously: a TH child can readily look away from the experimenter to view action taking place in a dollhouse and still listen to the experimenter’s narrative. For deaf children the traditional tasks often require shifting their visual attention from the tester to the test stimuli. Modified ToM measures can reduce the demands made on deaf children’s visual attention. For example, some researchers have designed storybooks that can be propped up underneath the experimenter’s face and in front of which the experimenter can sign (Schick et al., 2007), an adaptation that many signing parents use with their deaf children (Lieberman, Hatrak, & Mayberry, 2011).

Many oral deaf children rely not only on lip-reading, but also on what auditory information they can glean using their amplification systems. In the educational setting, teachers use a variety of amplification systems that transmit their voices directly to the hearing aids of the children in their classrooms, filtering out ambient background noise. Experimenters should also use such equipment when working with deaf children with some usable audition to maximize spoken language access. Close work with educators and speech therapists can create a testing situation that elicits an oral deaf child’s best performance.

For signing children, deaf native signing experimenters elicit children’s best linguistic performance. When a deaf native signing experimenter is not available, deaf or hearing fluent signers can also serve as experimenters. Some evidence indicates that deaf signers perform differently in the presence of non-fluent hearing signers, modifying their signs to conform less to the grammatical rules of the sign language (Cokely, 1983; Lucas & Valli, 1989). The least optimal testing situation is one in which a hearing non-signer administers the test and the language of the experimenter is translated by a sign language interpreter, commonly the classroom interpreter used in the program. In this situation, the child has to shift attention from the experimenter, to the interpreter, to the test stimuli. We know little about how well signing deaf children can shift their visual attention in such a situation (Corina & Singleton, 2009), and we know even less about how effectively young deaf children can use an interpreter. In studies with educational interpreters in the United States, 60% of the interpreters did not demonstrate advanced enough skills to ensure full access for children (Schick, Williams, & Kupermintz, 2006), and they were particularly deficient in conveying affect and prosody (Schick, 2004). More disturbingly, educational interpreters who are assigned to work with young preschool and elementary aged children typically scored the weakest on an assessment of educational interpretation (Schick et al., 2006). The very real limitations of using an interpreter to translate a non-signing experimenter’s instructions compromises the researcher’s ability to compare deaf children’s performance to that of TH children who are tested without the intervention of an interpreter. Low ToM performance in an interpreted situation may have more to do with task translation issues and controlling visual attention than true limitations in ToM reasoning.

Finally, to answer the question of whether language experience impacts ToM, researchers must work to ensure that any struggles observed in language-delayed deaf children are specifically associated with their general language ability, not just their ability to follow the instructions of the task. One way researchers have attempted to address this issue is to develop non-verbal or minimally verbal tasks that do not require children to understand complex language to succeed. Some (p.349) minimally verbal measures are classic FB tasks presented as picture sequences that are administered with minimal language support and that require children to make a forced choice between two or more alternatives (de Villiers & de Villiers, 2012; Pyers & Senghas, 2009, Schick et al., 2007; Woolfe, Want, & Siegel, 2002). Other minimally verbal tasks have been adapted from behavioral tasks used with non-human primates. These tasks engage the children in hide-and-seek games where they have to monitor the knowledge state of an informed or an uninformed confederate (Figueras-Costa & Harris, 2001; Schick et al., 2007).

A comprehensive study of false belief reasoning

Schick et al. (2007) most closely approximates the ideal design and control considerations laid out above. Unlike most of the previous work, Schick et al. tested a substantial sample of both orally taught (n = 86) and ASL signing (n = 90) deaf children to provide sufficient statistical power. Most importantly, sufficient numbers of native-signing DoD 4-year-olds were studied so that their performance on a variety of low and high verbal ToM tasks could be compared with that of TH children matched on SES, age, and non-verbal IQ. In addition extensive assessment of the children’s language acquisition was carried out, including measures of expressive and receptive vocabulary; receptive general syntax; and comprehension of tensed false complement clauses with verbs of communication (following de Villiers & Pyers, 2002). The oral deaf children were assessed in spoken English; the signing children (both the DoD and DoH groups) in American Sign Language (ASL). Special tests were developed to assess the ASL vocabulary, general syntax, and complement comprehension of the signing children. All of the testing was carried out by examiners with appropriate qualifications for working with either signing or oral deaf children: the signing participants by deaf examiners with native-signing ASL skills; and the oral deaf children by testers familiar with the speech of deaf children.

Schick et al. (2007) report several primary findings. First, language-delayed deaf children with hearing parents, whether they were educated in oral or signing schools, performed significantly worse on both high and low-verbal FB tasks than both the native-signing deaf children and the TH controls, indicating that the language demands of the standard tasks were not the cause of their poorer performance. Second, deafness alone does not affect ToM performance because native-signing deaf children and the TH control children performed at an equivalent level to each other on both the standard verbal FB tasks and the low-verbal analogs of the ToM tasks.

Hierarchical linear regression analyses determined whether background variables (age, hearing loss, non-verbal IQ, and sequence memory) or various aspects of the children’s language skills were predictive of their reasoning about states of knowledge and FB. Importantly, the same pattern of predictors was found for the oral deaf children (tested in spoken English) and the signing deaf children (tested in ASL). The performance of both the oral and the signing deaf children on the standard verbal FB tasks was independently predicted by age, receptive vocabulary, and the children’s processing of tensed false complement clauses with verbs of communication (as de Villiers & Pyers (2002) found for hearing preschoolers). Levels of hearing loss, non-verbal IQ, and sequence memory were not independent predictors of FB reasoning once age was controlled for. And comprehension of general syntactic features of spoken English or ASL was not as predictive of FB reasoning as vocabulary or processing of complement clauses. Passing the low verbal ToM tasks was independently predicted by age and processing of false complement clauses with communication verbs. The other background and language measures were not significant independent predictors for either oral or signing deaf children.

(p.350) Other studies of false belief reasoning in deaf children

Two other studies using low verbal FB reasoning tasks with native signing and late signing deaf children add important nuances to the findings of Schick et al. (2007), although they tested older samples of deaf children and did not provide the same degree of age and SES matching of deaf children with a control group of TH children. Woolfe et al. (2002) found that native signing children performed significantly better than late signers on a low verbal “thought bubble” test of FB reasoning, even though the two groups of children did not differ in their raw scores on a standardized test of British Sign Language comprehension. They argue that the native signing children’s early exposure to comprehensible conversation and language about their own and others’ mental states therefore is a more important factor in their ToM reasoning than their current knowledge of sign language syntax. Note, however, that the BSL assessment administered by Woolfe et al did not assess the children’s comprehension of false complement clauses. Schick et al. (2007) also found that general ASL syntax was not a significant predictor of ToM in signing deaf children; processing of false complements with verbs of communication was the strongest predictor.

Two studies by Meristo, Falkman, Hjelmquist, Tedoldi, Surian, & Siegal (2007) support the importance of ongoing comprehensible language and conversation in facilitating development of a well-articulated ToM. Native signers of Italian Sign Language (ISL) who were educated in bilingual educational environments that used ISL as well as spoken language outperformed native signers educated in oral-only instructional environments on the thought bubble FB reasoning task devised by Woolfe et al. (2002). There were no significant differences between native signers in oral environments, late signers in oral environments, and late signers in bilingual-bicultural schools. As was the case in the study by Woolfe et al., the ISL native signers in the two different educational environments performed at the same level on a test of their comprehension of ISL (an ISL translation of the test of comprehension of BSL). A second study of Estonian and Swedish deaf children showed similar findings when the children were tested on a battery of verbal FB and advanced ToM tasks. Again the authors stress the crucial role of fluent, comprehensible communication throughout the day for optimizing the ToM development of deaf children, even when the children have input in a natural sign language at home.

Finally, research on Nicaraguan deaf signers by Pyers & Senghas (Pyers, 2005; Pyers & Senghas, 2009) supports the notion that adult deaf individuals may acquire elaborate social interactional skills and function well in their communities, but unless they have acquired an appropriately complex syntax in their sign language, they may still fail low-verbal, but explicit FB reasoning tasks. Adults who were members of the early cohorts in the evolution of Nicaraguan Sign Language (NSL) were much poorer at reasoning about characters’ FB (or emotions based on FB) than younger individuals from the later sign language cohorts. The older, early cohort adults also had less complex and formally elaborated syntax in their NSL. In addition, when called upon to describe what was happening in brief videotaped scenarios of mistakes and deceptive actions (see de Villiers and Pyers, 2001), the older cohort used more language involving physical causation and desire-based explanations, while the younger cohort produced more mental state explanations with belief and knowledge verbs and complement clauses (Pyers, 2005).

All of these studies argue that language plays a crucial role in the ToM development of deaf children (and by extension, of TH children as well). Delays in the acquisition of mental state vocabulary, complex aspects of syntax that may enable representation of the content of false beliefs (de Villiers & de Villiers, 2009), and impoverished and less comprehensible communication may impair deaf children’s understanding of cognitive states, especially in situations where they are false. However, could the mechanism by which language delay has its impact on ToM understanding in deaf (p.351) children not be directly on the underlying conceptual development, but on the executive functioning skills that are needed for the explicit reasoning tasks by which the children are assessed?

Executive functioning and false belief reasoning

An influential account of children’s mastery of explicit reasoning about FB appeals to the development or maturation of executive functioning (EF) skills between the ages of 3 and 5. EF skills include the planning, monitoring, and control of behavior. Three aspects of the EF system have received most of the attention in research and theory about ToM development. First, inhibitory control, especially in situations of conflict between competing tasks or alternative behaviors (Carlson & Moses, 2001; Carlson, Moses, & Breton, 2002). Secondly, flexible rule following where there are conditional rules or set shifting when there are well-learned competing rules that the child needs to ignore (Frye, Zelazo, & Palfrai, 1995). Thirdly, working memory, which enables the child to keep the competing alternatives in mind (Davis & Pratt, 1995; Keenan, 2000).

Logical analysis of the usual FB reasoning tasks suggests that succeeding at them requires each of these three skills. In unseen location change tasks the child has to remember where the desired object was before and where it has been moved to and resist the lure of the current location of the object (reality) in order to respond correctly in terms of the false belief of the relevant character. Similarly, in the unexpected contents task the child is explicitly asked to remember what they thought was in the box before they looked inside, and therefore, they must inhibit the tendency to respond with what they have now seen has been substituted for the box’s usual contents. Several studies of TH children have reported significant correlations between one or more of these features of EF and ToM development, even when age and verbal IQ are controlled for (Carlson & Moses, 2001; Carlson, Moses, & Breton, 2002; Frye et al., 1995; Davis & Pratt, 1995).

EF and deafness

Several studies investigating EF and ToM in deaf children stand in contrast to the findings with TH children, and report that the inhibitory control and set shifting skills of deaf children do not seem to be closely related to their explicit reasoning about FB in verbal or low-verbal tasks. Woolfe et al. (2002) tested age-matched native signers and late signers in a version of the Wisconsin Dimensional Card Sort and found that although the native signers were significantly better than the late signers on a low-verbal FB reasoning task, there was no difference between the two groups on the set-shifting task. Similarly, Meristo & Hjelmquist (2009) tested three groups of deaf students matched for age and non-verbal IQ: bilingually-instructed native signers, orally-instructed native signers, and bilingually-instructed late signers. The children were given a battery of verbal ToM and executive function tasks (administered in sign language by native signing research assistants). Although the native-signing deaf children from the bilingual educational settings were significantly better than the other deaf groups on the ToM reasoning tasks, there were no significant differences between the groups in verbal working memory (backwards digit span), set shifting (on the Wisconsin Card Sorting test) or conflict inhibitory control. Furthermore, when age and non-verbal IQ were partialled out, only verbal working memory was significantly correlated with FB reasoning on the standard verbal tasks. There was no correlation between conflict inhibition or set shifting and FB reasoning for the deaf children.

de Villiers & de Villiers (2012) studied 45 oral deaf children and 45 TH controls on a battery of EF, language, deception, and FB reasoning tasks. The younger of the deaf children (average age 5;3, range 4–6, n = 29) were closely matched with 18 of the hearing children (average age (p.352) 5;2, range 4–6) in age and non-verbal sequence memory. There were no significant differences between these two matched groups of children on widely used EF tasks that included a two measures of conflict inhibitory control (the Day-Night Stroop test and the Knock-Tap hand game) or on a dimensional card sort set shifting task. However, the deaf children were significantly worse than the hearing children on both the standard verbal FB unseen object displacement and unexpected contents tasks and on two low verbal “thought bubble” tests of FB understanding based on the procedures used by Woolfe et al. (2002) and Schick et al. (2007). Furthermore, the deaf children were significantly impaired relative to the TH children in their mastery of general English sentence syntax and their memory for false complement clauses with verbs of communication (de Villiers & Pyers, 2002; Schick et al., 2007). For both the deaf and the TH groups, performance on the FB tasks was independently predicted by the children’s language and especially by their processing of false complement clauses, even when age and sequence memory were controlled for. None of the EF measures predicted FB reasoning in the deaf children, and they were weaker predictors than the language measures were for the hearing children.

Taken together, these studies with deaf children show that while EF may be necessary for success at explicit FB reasoning tasks, these skills are not the proximal predictors of deaf children’s level of performance on those tasks (see also de Villiers, 2005). The strongest predictors seem to be the children’s language skills.

Interestingly, on two low verbal deception games (the sticker-in-the-hand game and a deceptive pointing game) there were no significant differences between the deaf children and the hearing children in level of performance (de Villiers & de Villiers, 2012). The children’s deception scores were significantly predicted by their sequence memory and their inhibitory control, not by their language. Thus, there seems to be a dissociation of deception and explicit FB reasoning tasks for deaf children: the deaf children were on a par with their hearing peers on deception games, but showed significant delays in explicit FB reasoning even when the language demands of the tasks were minimized. de Villiers & de Villiers (2012) suggested that deception at this level could be handled by behavior rules without explicit representation of mental states (cf. Perner, 2010; Poivinelli & Vonk, 2004; Ruffman, Taumoepeau, & Perkins, 2012).

Continued growth in ToM reasoning in deaf individuals

A few of the earlier cross-sectional studies of FB reasoning in deaf individuals suggested that their impaired language acquisition and impoverished communication might produce lasting deficits in ToM, hinting at a critical period for the development of a conceptual understanding of FB (Edmondson, 2006; Morgan & Kegl, 2006; Russell, Hosie, Gray, Scott, Hunter, Banks, et al., 1998). However, two more complete longitudinal studies have documented acquisition of FB understanding even as late as early adulthood. Deaf Australian elementary school children showed delayed, albeit eventual, acquisition of FB understanding on standard verbal tasks (Wellman, Fang, & Peterson, 2011). Some members of a population of adult Nicaraguan signers who, as children, acquired a new, emerging sign language that had limited mental-state vocabulary initially failed low-verbal FB tasks, but after the very same signers acquired verbs of belief and knowledge as adults, they subsequently improved their FB performance on a low verbal FB task (Pyers & Senghas, 2009). This pattern of late acquisition provides strong evidence that the acquisition of FB understanding is not bounded by a critical period. Crucially, all participants in the study of Nicaraguan signers had otherwise typical social and environmental experience—their sole limitation was related to the complexity of their mental-state language. In extreme cases of deprivation—nutritional, social, and language—late acquisition of FB understanding may not be possible.

(p.353) Development of other aspects of theory of mind

As in the case of research on TH children, study of ToM development in deaf individuals has been dominated by research on FB understanding in preschool and early elementary school. However, ToM development begins in infancy as children begin to exhibit attention to other’s minds by following the eye-gaze of others (Brooks & Meltzoff, 2002), engaging in joint attention (Tomasello, Carpenter, Call, Behne, & Moll, 2005), and understanding others’ goals and intentions (Meltzoff, 1995). Similarly, FB understanding in the late preschool years is preceded by an understanding of how knowledge is acquired, specifically how seeing and knowing are related (Flavell, 1992; Pratt & Bryant, 1990), and of non-belief mental states, such as desires (Bartsch & Wellman, 1989). This section of the chapter reviews the research on those other components of ToM development in deaf children and considers the way in which language delay may impact them.

Intention and desires

Children’s first insight into others’ minds emerges when they first see humans as intentional agents. Between 10–12 months of age, infants show sensitivity in looking-time measures to the goals not the means of human action (Gergly, Nádasdy, Csibra, & Bíró, 1995; Sommerville & Woodward, 2005). By 18 months, toddlers readily imitate the goal of a human’s novel, but incomplete action (Meltzoff, 1995). Crucially, an understanding that behaviors are in the service of goals marks this early understanding; toddlers do not slavishly imitate the behavior of a model, but will vary their behavior to achieve the apparent goal of the model.

One study with deaf 4–7-year-olds demonstrated equivalent performance to TH children on a gesture imitation task, with both groups making imitation errors that violated the way in which the hand moved, but remaining faithful to the ultimate goal of the movement trajectory (Want & Gattis, 2005). This pattern of errors indicated that, by 4 years of age, both hearing and deaf children had represented the goal of the action. However, an understanding of intentionality begins in infancy, and we know little of whether deaf infants struggle with an early understanding of intentionality, but overcome this delay by age four.

Several studies have shown that deaf children of hearing parents also show delays in reasoning about desires and intentions. The first showed that deaf children of hearing parents struggle to interpret the intention- and desire-based meanings of eye gaze, failing to correctly infer the desire and intentions represented in a schematic drawing of a face, with only 9-year-olds exhibiting performance similar to that of TH 4-year-olds (Scott, Russell, Gray, Hosie & Hunter, 1999). This delay is quite striking given that pre-linguistic 10-month-olds with normal hearing reliability reliably follow the eye gaze of an experimenter (Brooks & Meltzoff, 2005) and TH 2-year-olds infer desire from eye gaze at above chance levels (Lee, Eskritt, Symons, & Muir, 1998). More low-verbal behavioral tasks conducted with deaf toddlers are needed to fully understand the degree to which language experience affects an understanding of intentionality and desire.

Three other studies that have addressed deaf children’s desire reasoning have been in the context of predicting and explaining emotions. Oral deaf children between the ages of 5 and 10 who failed FB tasks also struggled to predict a character’s emotion based on their desires, although they were less impaired on the desire-based emotion items than on the FB-based ones (Pyers & de Villiers, 2003). However, deaf 6-year-olds enrolled in a school where emotion reasoning was emphasized in the curriculum were actually more likely to explain emotions in terms of underlying desires than their TH peers (Rieffe & Terwogt, 2000).

(p.354) In the population of Nicaraguan signers, understanding of desire-based emotions and FB-based emotions were clearly dissociated: failers of a low-verbal FB task readily predicted emotions based on a character’s desire in a minimally verbal task (Pyers & de Villiers, 2003; Pyers, 2005). Thus, any limitation in reasoning about desires seems to be overcome before success on FB tasks, and deaf children’s understanding of desires as a source of behaviors and emotions appears more robust than their understanding of false beliefs. This is in keeping with the proposal by Wellman (1990) that a desire-based ToM emerges before a belief-based one.

Sources-of-knowledge

Understanding FB is contingent upon understanding how other people’s perceptual experiences influence their knowledge states—if the boy does not see the chocolate moved from the cupboard to the refrigerator, he does not know where it is. Thus, understanding the relationship between sensory perception and knowledge should develop before an understanding of FB (Wellman & Liu, 2004). By age three TH children readily understand Level 1 visual perspective taking—that if someone cannot see the object you can see, that person does not know the identity of the object (Flavell, Everett, Croft, & Flavell, 1981). Yet this understanding does not readily generalize to all senses simultaneously. Children who understand the relationship between seeing and knowing do not seem to exhibit the same understanding of the relationship between feeling and knowing, and they struggle to understand the modality specific nature of knowledge, e.g. that you cannot identify the color of an object by only touching it (O’Neill, Astington, & Flavell, 1992).

Wellman & Liu (2004) included in their ToM scale a “knowledge access” task that taps children’s understanding of the relationship between seeing and knowing. Deaf children of hearing parents exhibit delays relative to TH peers on this task, but just like the TH children, they master this concept before they pass traditional FB tasks (Peterson, Wellman, & Liu, 2005; Wellman, Fang, & Peterson, 2011). The “knowledge access” task is a bit more difficult than the traditional seeing-knowing tasks in that it involves complex language, requires the child to inhibit their own knowledge of the object’s identity (e.g. Birch & Bloom, 2003), and asks the child to predict another’s state of ignorance rather than to report who would be a knowledgeable informant (e.g. O’Neill & Gopnik, 1991; Robinson, Haigh, & Pendle, 2008). Nevertheless, language-delayed deaf children’s limitation in understanding seeing and knowing was also observed using a minimally verbal task adapted from Povinelli & de Blois (1992). Deaf children of hearing parents exhibited delays on this task, and their performance correlated with their performance on a low-verbal FB measure and with their language skills (Schick et al., 2007).

Oral deaf children of hearing parents are also delayed relative to TH children on a task adapted from Pratt & Bryant (1990) that taps the seeing-knowing and hearing-knowing relationships. While hearing children succeeded on this task by 4 years of age, deaf children of hearing parents did not pass the task until 5.5 years of age (Schmidt & Pyers, 2011). Most importantly, deaf children are were equally delayed on both sensory modalities, even though they have had more limited experience with auditory information relative to visual information. Thus, on a variety of low and high verbal tasks assessing their understanding of the relationship between sensory perception and knowledge, DoH children acquire this understanding well after the age at which typically developing children master it.

Early implicit false belief understanding in indirect tasks

A rapidly growing body of research suggests that in addition to an early understanding of people’s goals and intentions, by age 2 or so toddlers have an implicit understanding of others’ states (p.355) of knowledge and beliefs, even when those beliefs are not in keeping with reality (Baillargeon, Scott, & He, 2010; Low & Perner, 2012). It is not clear how elaborated those concepts are at this age, but they appear to be sufficiently robust to drive toddlers expectations, selective attention, and anticipatory looking. Some researchers have argued that the difference between this early evidence for understanding of FB and the later emergence of explicit reasoning about FB around age 4 lies in the methods used to assess the children’s knowledge. Traditional FB tasks and their variants directly ask about a character’s belief or behavior; the research on infants and toddlers uses indirect tests that infer the children’s understanding from their eye gaze, anticipatory looking, or spontaneous helping behavior (Baillargeon et al., 2010; Buttelman, Carpenter, & Tomasello, 2009).

Theorists differ on how they regard the difference between children’s apparent knowledge on indirect vs. direct tests of FB understanding. Clements & Perner (1994) suggested that anticipatory eye gaze reflected an “implicit” understanding of false belief, and an understanding shown on indirect, but not direct tests of a concept is considered a hallmark of implicit or unconscious knowledge in the literature on consciousness (Low & Perner, 2012). Apperly & Butterfill (2009) suggest there may be two conceptual systems in ToM development: an early-emerging unconscious system that tracks “belief-like” states and is sensitive to another person’s engagement with or access to an object or event, and a more abstract, explicit system of concepts with a more articulated representation of the propositional content of beliefs and states of knowledge. Others (e.g. Perner, 2010; Ruffman, Taumoepeau, & Perkins, 2012) have distinguished between the early learning of behavioral regularities or rules that may be more situation-specific, and support expectations and spontaneous behaviors without reference to mental-state representations.

These positions continue to maintain that there is maturation or learning of new conceptual representations in the early preschool years that is reflected in the children’s performance on traditional direct tests of FB understanding (Perner, 2010; San Juan & Astington, 2012; Wellman, Cross, & Watson, 2001). In contrast, other researchers argue that the infant and toddler research shows that the core concepts of ToM, including FB, are available to children during the second year of life and may be a part of an innate or early-maturing ToM module (Baillargeon et al., 2010; Leslie & Polizzi, 1998; Roth & Leslie, 1998). However, toddlers cannot make use of that knowledge in the direct, explicit FB reasoning tasks that are used to assess FB because of limited EF resources such as working memory and inhibitory control, skills that are required by those tasks.

The research on EF in deaf children described earlier (de Villiers & de Villiers, 2012; Meristo & Hjelmquist, 2009; Woolfe et al., 2002) indicates that while inhibitory control and set shifting may be prerequisites for success on explicit FB reasoning tasks, those aspects of EF do not seem to be the proximal causes of different levels of performance in those tasks. Language and exposure to fluent communication appear to be the more important proximal predictors. However, we know little to nothing about the early development of EF in deaf children (Marschark, 1993; Marschark & Spencer, 2011).

The research on different aspects of ToM in deaf children that we summarized above all used direct, explicit measures of the children’s understanding and reasoning, even when verbal demands of the tasks were minimized. But would language delayed deaf children with hearing parents show early-emerging implicit ToM understanding in the indirect, spontaneous procedures developed for studying TH infants and toddlers? Gale et al. (2009) and de Villiers & de Villiers (2012) demonstrated that on a low-verbal sticker-in-the-hand hide-and-seek game that involved spontaneous deception, language delayed signing and oral deaf children were not delayed in their deceptive behaviors relative to native signing deaf children or matched TH controls, but the youngest children in their studies were 4 years of age.

(p.356) In a small-scale study of 10 deaf DoH toddlers (17–28 months) with hearing parents Meristo et al. (2012) compared their anticipatory looking in a non-verbal true belief and FB scenario with the same behavior in age-matched TH toddlers matched for age. The parents of the deaf children used spoken Swedish supported by some signs from Swedish Sign Language, but none of the toddlers had mastered many signs. Half of the deaf children had cochlear implants and the other five used hearing aids.

All of the children watched videotaped scenarios in which the familiar cartoon mouse Jerry ran down a tunnel in the shape of a Y and hid in one of two boxes at the end of each arm. He was then followed down the tunnel by the cat Tom. On the test trials Jerry changed his hiding place from one box to the other before Tom entered the tunnel. On the true belief trial Tom was present in the video and saw Jerry move from one box to the other; on the FB trial Tom was not present when the change of location took place. Half of each group of children saw a true belief trial followed by a FB trial; the other half saw the trials in the opposite order. An automated eye tracker measured how long the toddlers watched the exits from each arm of the Y-tunnel or the boxes they led to once Tom entered the tunnel. The TH toddlers spent significantly more time looking at the location that Jerry had moved to in the true belief condition, but significantly more time looking at the empty location (where Tom last saw him) in the FB condition, indicating that their spontaneous attention was sensitive to Tom’s state of knowledge. The deaf children also looked more at the correct exit and box in the true belief condition, but in the FB condition they all still looked at the box containing Jerry and none of them looked at the empty box or exit that corresponded to Tom’s FB about where he had last seen the mouse.

These deaf toddlers did not show the sensitivity to the character’s belief state in spontaneous, anticipatory attention that was demonstrated by the hearing children. Meristo and colleagues suggest two possible interrelated reasons for this result: first, that impoverished communication between the hearing parents and their deaf children impairs the children’s acquisition of mental-state concepts or of joint attentional processes that build on the children’s gestures and pointing; and second, that early language sharing in hearing caregiver-child dyads may enhance executive functioning abilities that are necessary in this anticipatory looking task where the child has to inhibit the lure of reality and look away from the box containing the mouse. The impoverished communicative interaction between hearing caregivers and their deaf infants and toddlers might delay that EF development. As we point out above, EF does not seem to be delayed at age 4 in language-impaired deaf children with normal range non-verbal IQs and memory development when it is tested in low verbal tasks; but we do not know whether the earliest emerging components of EF are impaired prior to age 3 in these children.

Considering the role of joint attention

DoH children with delayed language acquisition seem to experience broad delays in understanding others’ mental states in addition to their difficulties with explicit reasoning about FB. Both joint attention and language may play a causal role in DoH children’s impaired ToM, and they both are likely to interact, as language and gestural communication seems to play a crucial role in the development of joint attention (Slaughter, Peterson, & Carpenter, 2009).

Joint attention, the ability to manage attention to both a communication partner and another thing or event, has been posited as a precursor to a full-blown ToM (Moore & Corkum, 1994). Children with autism show delays in joint attention with greater delays in initiating rather than responding to joint attention (Mundy, 2003). DoH children also show some limitations with respect to joint attention, and these limitations may have long-ranging consequences for both their language acquisition and social-cognitive development.

(p.357) Overwhelmingly, the findings about joint attention in deaf children come out of observational studies of parent-child interaction, and these observational studies show that DoH children have much less experience with joint attention and the quality of that joint attention is significantly poorer than what is observed in typically hearing children. Hearing parents spend less time engaging in coordinated joint attention with their deaf 12- and 18-month-olds than deaf parents with deaf children and hearing parents with hearing TH children (Meadow-Orlans & Spencer, 1996). This limitation in joint attention seems to persist into the second year of life, with deaf 24-month-olds with hearing parents experiencing fewer sustained bouts of joint attention than typically hearing dyads (Gale & Schick, 2009). Another study with slightly different findings showed that DoH children spent more time than hearing children in coordinated joint attention, but the quality of this time was strikingly different. For deaf children, almost none of this time was in symbol-infused joint attention where children were exposed to new words (Prezbindowski, Adamson, & Lederberg, 1998).

That the quantity and quality of joint attention for DoH children is significantly lower than for typically developing children may be the origin of an array of ToM delays. First, joint attention seems to be the hallmark of uniquely human social cognition (Tomasello, Carpenter, Call, Behne, & Moll, 2005). When sharing attention with another person, infants are afforded an opportunity to learn that intentions and goals can be shared (Tomasello, 1995). While the amount of joint attention experience required to support an understanding of shared intentions and goals is unclear, one study comparing hearing infants to deaf infants with and without cochlear implants, showed that more time in joint attention positively correlated with higher maternal perception of social competence (Tasker, Nowakowski, Matilda, & Schmidt, 2010), a finding that is further bolstered by longitudinal studies with typically developing children that have shown that infants’ engagement in joint attention at 20 months positively correlates with their performance on a battery of theory of mind measures at 44 months of age (Charman, Baron-Cohen, Swettenham, Baird, Cox, & Drew, 2000). Beyond the amount of joint attention engagement, the quality of joint attention also impacts later ToM development. In a longitudinal study, maternal sensitivity to their infant’s internal states at 10 months, a measure that included commenting and elaborating on joint attention, was highly correlated with children’s FB scores at 54 months (Ereky-Stevens, 2008).

While experience with joint attention allows for the child to experience a “meeting of the minds,” joint attention is where early language learning is situated, and children’s engagement in joint attention is predictive of their later language ability (Carpenter, Nagell, & Tomasello, 1998; Mundy & Gomes, 1996; Tomasello & Farrar, 1986). Specifically the degree to which infants respond to bids for joint attention positively correlates with their receptive and productive vocabulary scores at 30 months (Morales, Mundy, Delgado, Yale, Messinger, Neal, & Schwartz, 2000). The relationship between joint attention and language development is present earlier in development: reliably following gaze at 10 months of age predicts vocabulary scores at 18 months (Brooks & Meltzoff, 2005). The early impact that joint attention has on vocabulary development likely also has consequences for more complex language development, such that the language delays faced by deaf children because of their hearing-impairment may be compounded by their limited joint attention experience.

The development of ToM and of language is dependent upon extensive experience with high-quality, symbol-infused joint attention. As such, the ToM delays observed in most deaf children of hearing families may originate in the hearing parents’ struggle to engage in joint attention with their deaf children; none of the observational studies of deaf children observed children’s failure to point or to follow eye-gaze as has been observed for children with autism. Instead, deaf children exhibit the appropriate joint attention behaviors, but they are given limited opportunity (p.358) to engage in them. This limitation has a two-fold impact on deaf children’s ToM development. First, what is seen as one of the key precursors to a mature ToM is impoverished, likely impacting later developments in ToM reasoning. Secondly, the limited experience with joint attention can delay language development and language is highly predictive of successful FB reasoning during the preschool years (see Milligan, Astington, & Dack, 2007 for a review). Thus, a key locus of ToM intervention for deaf children with hearing families may be in teaching hearing parents how to initiate and sustain high-quality joint attention with their deaf children who have the capacity, but limited opportunity, to do so.

Conclusions

The case of DoH children sheds light on the way in which environment, specifically language experience, shapes the development of a mature ToM. The research on ToM in deaf children that we have summarized in this chapter leads us to several conclusions:

  1. 1. Language acquisition and comprehensible communication from infancy are essential for the development of ToM on a normal timetable. DoH children with language delays and impoverished communicative interactions are significantly delayed in several aspects of their ToM development.

  2. 2. Initial evidence suggests that this delay in ToM includes not only explicit, propositional reasoning about FB and states of knowledge in preschoolers, but also implicit, spontaneous expectations and anticipatory behaviors in infants and toddlers. Much more research is needed on these early stages of ToM understanding in both language-delayed deaf toddlers and native signing deaf children.

  3. 3. Any impairment in communication between hearing caregivers and their deaf children may lead to failures in initiating and sustaining high-quality joint attention with their deaf infants may contribute to both further language acquisition delays and to impaired understanding of the mental states of others.

  4. 4. The degree of impairment seen in explicit ToM tasks is most strongly predicted by the acquisition of complex language by the deaf children and by the degree of language delay that they experience. Early interventions with a comprehensible natural sign language or effective amplification systems enhance spoken language acquisition (Remmel & Peters, 2009) can considerably mitigate these delays in social cognition.

  5. 5. Development of a fully articulated ToM seems to not be constrained by a critical period, and can continue well into later childhood or even adulthood (Peterson, 2009; Pyers & Senghas, 2009; Wellman et al., 2011). Thus, the research on the development of ToM in deaf children has not only led to a better understanding of the importance of language experience in that development, it has argued against any strong critical period for ToM development and provided some optimism for the effectiveness of interventions to facilitate deaf children’s social cognitive development.

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