The primary goal of this study was to examine the post-acute effects of TBI on first-order ToM skills in 3- to 5-year-old children. Contrary to expectations, TBI did not adversely affect the ability of our TBI sample as a whole to engage in representation of mental states at a developmental level comparable to their peers. We should emphasize that our lack of group differences on false-belief tasks does not rule out the possibility of differences on other aspects of mentalizing or social perspective taking (Bloom & German, 2000
). We would also point out that our findings are consistent with two previous studies that failed to demonstrate deficits in first-order ToM tasks in children who sustained TBI at later ages than those in our sample (Snodgrass & Knott, 2006
; Turkstra, Dixon, & Baker, 2004
However, our analyses did reveal that 3-year-old children with TBI performed more poorly than same aged children with OI on one of the two appearance-reality measures administered, the apple-candle task. Typically developing children under 4 years are prone to realism errors on false-belief tasks (Rice et al., 1997
). For the apple-candle task, a typically developing 3-year-old child would say that the object is a candle and
looks like a candle, once they discover the reality that the object is
really a candle. Specifically, although similar percentages of children at this age level in the TBI and OI groups (63% versus 71%) said the object looked like an apple, a much lower percentage of those with TBI (38% versus 71%) went on to say that the object was really a candle. One explanation is that the appearance (i.e., looking like an apple) was significantly more salient for the children with TBI and thus, they showed a bias towards that property of the object. Another possibility is that the 3-year-old children with TBI were hampered by the information processing and working memory demands of the task. Once the object was sitting in front of them again, looking like an apple, they were unable to hold in their mind that they had discovered the object was really a candle (Rice et al., 1997
). The performance of 3-year-olds on our second appearance-reality task was likely confounded with knowledge of colors, leaving us with a reduced and potential biased sample of 3-year-olds, particularly within the TBI group. Eighteen of the 21 3-year-old children with OI were able to complete the color filter task, but only 9 of 16 3-year-olds with TBI knew colors well enough to do so.
Analyses revealed that children with severe TBI were significantly impaired relative to the OI group and the moderate TBI group on the false contents score, with results from post-hoc analyses suggesting that the children with severe TBI were more prone to realism errors. Across all three of the false contents tasks, only 25% (4/16) of the children with severe TBI were able to acknowledge their previous belief that they had expectations for what was in the container that differed from reality, compared with around 50% (44/86) of those with OI. Although the findings from our appearance-reality and false-contents tasks could appear contradictory, the tasks may elicit different biases in children with TBI (Rice et al., 1997
; Flavell et al., 1986
). In other words, for children with TBI the appearance may have been the more salient property in the candle-apple task, whereas the reality was the more salient property in the false-contents tasks. Moreover, performance on both tasks likely was impacted by the cognitive consequences of moderate-to-severe TBI (Taylor et al., 2008
). Recent research suggests that poor performance on ToM tasks following pediatric TBI is related to communication skills and executive functions, such as language pragmatics, working memory, and cognitive inhibition (Dennis et al., in press
; Dennis et al., 2001
; Dennis, 1991
; Yeates et al., 2007
Our regression analysis revealed that age and overall cognitive ability were strong predictors of first-order ToM performance independent of injury type, a result consistent with the normative developmental literature. These findings indicate that false-belief tasks are cognitively complex and that performance is related to children's cognitive competencies (Bloom & German, 2000
). Interestingly, although IQ was strongly related to performance in healthy children, task performance was independent of IQ following moderate or severe TBI. One plausible explanation for this finding is that the children with TBI have selective (i.e., IQ-independent) impairments in cognitive domains related to ToM skills, rendering IQ a relatively poor predictor. In children without TBI, in contrast, IQ may be more representative of other ability domains, making IQ a better predictor of ToM. Another possibility is that the first-order ToM tasks are too difficult for children with lower IQ regardless of injury type, with floor effects on the ToM tasks precluding detection of group differences in children of lower ability.
More generally, the findings suggest that children who sustain TBI in early childhood are susceptible to deficits in first-order ToM skills, but that these deficits are likely to be subtle and dependent on children's age and overall cognitive functioning. One explanation for the lack of more uniform deficits in these skills is that TBI renders young children most vulnerable to impairment in the specific skills that are emerging and undergoing rapid development at the time of injury. In support of this possibility, the post-acute effects of TBI may not be readily apparent on tasks that have been previously mastered (e.g., appearance-reality tasks for 5-year-olds) or are yet to develop (e.g., false-contents tasks for 3-year-olds).
The results of this study invite exploration and speculation about the specific mechanisms and neural pathways involved in performance on ToM tasks following early childhood TBI. Because imaging available on our sample at the time of injury was limited for the most part to acute CT scans, we lacked the more probing measures of brain status (e.g., using magnetic resonance imaging) that would be needed to relate the integrity of specific brain regions or networks to the ToM tasks. However, one potential basis for the deficits in ToM observed in this study is the susceptibility of children with TBI to brain insults in anterior and medial frontal regions. Evidence that insults to these regions contribute to deficits in social skills and social information processing may help account for the differences observed (Yeates et al., 2007
Study limitations in addition to the absence of comprehensive brain imaging include the lack of information on other severity variables, such as length of post-traumatic amnesia, primarily because of the difficulty of accurately documenting this information in young children. Although our regression analysis considered data from the total sample, a final limitation was the relatively small sample size available for evaluating the effects of age and TBI severity. Without recruiting children from a larger population base, studies of children with TBI falling into restricted age ranges and with highly variable developmental status are likely to continue to face problems of this sort. As other researchers have suggested, outcomes following TBI in early childhood may be even more variable than in other age groups because of the effects of early brain insult on neurogenesis or postinjury skill development (Anderson et al., 2005
; Barnes et al., 1999
, Ewing-Cobbs et al., 1997
, Taylor & Alden, 1997
The results of this study suggest a number of important research directions as we continue to follow this cohort. Most importantly, following the development of ToM skills over time in this cohort of young children will help to determine if ToM skills worsen, remain stable, or improve over time relative to the OI group. We will also be able to relate the development of ToM skills to the child's social environment and development of social competence and other neurobehavioral skills. For example, further investigation of the relationship between ToM skills and executive functioning will likely contribute to the longstanding debate on the nature of the overlap of these two processes. Given the importance of social and behavioral competence to academic success and emotional well-being, study of the relationship between ToM skills and social competence will be another important future direction. If ToM skills are dependent on social interactions and adequate social communication, we might hypothesize emergence of group differences in ToM performance over time as TBI has an impact on social outcomes and interactions.
Other critical research needs include application of advanced neuroimaging techniques to elucidate the relationship between neural substrates and ToM abilities; assessment of children injured at even earlier ages to determine the effect of TBI sustained prior to the emergence of first-order ToM skills; and efforts to better understand the reasons for children's failures on ToM tasks. Manipulating the information processing demands, such as deception and intention, will be particularly important as the field moves towards developing interventions to improve social outcomes following early childhood TBI. The present findings offer tentative support for deleterious effects of TBI in young children on at least some aspects of first-order ToM skills and emphasize the importance of considering age and overall cognitive ability as predictors of outcome. First-order ToM deficits should be taken into account in assessment and interventions with 3- to 5-year-old children with a history of TBI.