Intellectual and Adaptive Abilities

As expected, FSIQ results, representing overall level of cognitive functioning, indicated that children with severe TBI were most compromised postinjury. While all TBI groups demonstrated an improvement over time, the increment for the mild and moderate TBI groups was modest in contrast to that recorded by the severe TBI group. Therefore, in keeping with previous research (Chadwick et al., 1981a, 1981b, 1981c; Jaffe et al., 1992, 1993, 1995), this study provides firm evidence that severe TBI is associated with impairments of intellectual function, and that there is a pattern of recovery of these skills for children with severe TBI. In keeping with these findings, the PS Index exhibited an initial dose–response effect, with all groups showing some improvement over time. There was, however, no differential improvement for the severe TBI in this instance, supporting the findings of Donders and Warschausky (1997) who reported that PS Index was impaired following childhood TBI. Subtle coordination difficulties observed post-TBI (Catroppa et al., 1999) may explain the poorer recovery of these processing skills. In contrast, results for the FFD factor showed no significant injury-related trends. There is a need for further follow-up of this group once these skills are fully developed, as subtle difficulty at an early age may be predictive of persistent compromise on tasks requiring higher order skills in the adolescent/adult years, consistent with deficits in executive function post-TBI (Levin et al., 1997).

Adaptive functioning results from the VABS suggested similar skills across groups preinjury, with the mild TBI group performing similarly pre-TBI and post-TBI. In contrast, moderate and severe TBI groups performed more poorly post-TBI, with the severe TBI group showing most “deterioration”. These results suggest that, with regard to adaptive living skills, parents of children who sustained a moderate/severe TBI perceived that their child was not developing at an expected level in a number of adaptive functioning areas.

Behavioral Function

Results on the parent-based RBRI based also indicated a dose–response relationship. Parental ratings indicated that by 6 months postinjury, the degree of maladaptive behavior in the moderate and severe TBI group, but particularly the severe TBI group, had increased from preinjury levels, and that this maladaptive behavior continued to the 24-month period. These results argue that, following more severe TBI, behavioral indices of attention may not recover, but may reflect ongoing impairment in this domain, which may interfere with ongoing development. Interestingly, parental responses on the RBRI predicted performance on clinical tests of attention, suggesting a relationship between observable attentional difficulties in everyday settings and those measured by more standardized measures. Teachers rated the moderate TBI group as most behaviorally compromised. A number of possible explanations for these findings may be considered. First, the perception of acceptable behavior will differ between parents and teachers, biasing responses made to particular questions. Parents and teachers may also differ in the behavior samples they observe. For example, a child with severe TBI may be slow and non-active in class, while at home, such behavior may be considered out of character and problematic for that child. Second, children with severe TBI often receive individual assistance within class and this may mask the level of maladaptive behavior present in less supervised conditions. Further, children with severe TBI and more obvious deficits, may have less expectations placed on them than those with less obvious impairments. However, of importance, both parent and teacher responses indicated that behavioral difficulties are often present following moderate to severe TBI. Finally, both teacher and parent reports indicated that behavior did not improve with time since injury, especially for the moderate and severe TBI groups.

With regard to the NRS, parents of children with severe TBI reported a high frequency of attentional difficulties at 12 months postinjury. Conversely, only a small percentage of children who sustained a mild TBI were reported as having attentional difficulties. A minor limitation to be considered when interpreting the NRS is that there is no preinjury score for comparison. However, both parental reports, the RBRI and NRS, report attentional difficulties to be increasing from preinjury levels for the severe TBI group. Consistent with other findings, these results suggest a dose–response with more severely injured children presenting with more maladaptive behavior.

Attentional Measures

Results on the attentional and information processing tasks indicated a consistent dose–response relationship. In contrast, recovery patterns varied depending on the specific attentional component being measured. This variability in recovery may depend on the specific cerebral region impacted by injury, and its level of maturity at the time of injury. On measures of sustained attention, children with severe TBI achieved fewest correct responses, had problems maintaining attention and working efficiently over time, showed a gradual increase in errors with time on task, and presented with a vigilance decrement.

When considering mean reaction time for correct responses, there were no significant main effects for Group or Time, consistent with much of our previous research. However, with regard to performance between Blocks 1 and 4, the severe TBI group appeared to respond more quickly over time. While this finding may be considered unexpected based on adult and adolescent TBI data, Maule et al. (2000) postulated that this finding may be explained in terms of time pressure and high levels of anxiety and energy, that is during lengthy and complex tasks, children with severe TBI felt more anxious and pressured, and so responded more impulsively. For missed responses, analysis revealed a number of significant results. While a dose–response result was evident, all TBI groups missed more responses at the end of the task, with the severe TBI group achieving the highest number of missed responses in the last 5 min at each time point. Such findings are consistent with a number of previous studies (Timmermans & Christensen, 1991; Kaufmann et al., 1993) where children with TBI demonstrated significant difficulties sustaining attention.

Analysis of omission and commission errors revealed a similar pattern, with best performance by the mild TBI group and poorest by the severe TBI group. Over 6–12 months post-TBI, the severe TBI group tended to make less errors of omission and commission, perhaps due to the fact that they had more missed responses toward the end of the task at each time point postinjury. As suggested earlier, it may be that long periods of time pressure may lead to fatigue, resulting in more errors over time (Maule et al., 2000). For impulsive errors, results revealed that the severe TBI group made more errors at each evaluation, and more errors toward the end of the task. Some may suggest that impulsive errors may in fact be ‘late’ responses (a slow response from the previous stimuli), however, analysis of the data did not support this interpretation.

For selective attention, results were in the expected direction, with significant differences between the severity groups. Results also support the possibility of information processing deficits, as the severe TBI group took longest to complete timed tasks, especially when visuo-motor speed and coordination were integral to the task. The severe TBI group showed substantial improvement over time, suggesting recovery over time rather than a general practice effect for all TBI groups. These findings provide partial support for findings in the adult literature where reduced speed of information processing has been implicated as a confounder on tasks measuring attentional skills (Anderson & Pentland, 1998; Ponsford & Kinsella, 1992; Stuss et al., 1989). However, our results suggest that these problems are specific to visuo-motor performance with simple processing speed (i.e., reaction time) intact.

For both simple and complex tasks of shifting attention, results suggest both practice effect and recovery for moderate and severe TBI groups. Again, results indicate slower performance for those who sustained greater injury, but with a steeper recovery over time. It is difficult to determine whether the poorer performance is one of shifting attention, or whether there is an inability to shift attention in conjunction with slowed visuo-motor processing. Such an interpretation is consistent with Wood's argument, where he stated that head injury may limit attentional capacity. It can reduce the extent to which attention can be divided across stimuli and so may affect one's ability to “shift” their mode of thinking, resulting in slower and even less reliable processing of information (Wood, 1988). For tasks that involve verbal rather than visuo-motor responses, it may be suggested that children who sustained a significant injury presented with an exacerbation of difficulties as shifting attention, working memory, and processing speed all appeared compromised, not surprising, considering the diffuse nature of pathology often associated with TBI. Furthermore, for tasks of high complexity, those with greater injury presented with both slower performance and higher error rate. However, it may be suggested that if the time pressure is removed, then errors may decrease. This pattern was seen using an experimental CPT paradigm (Catroppa & Anderson, 2003), where increasing the interstimulus interval resulted in no significant differences between severity groups.

Summary and Limitations

Traumatic brain injury results in a number of changes to brain tissue, depending on the type of damage incurred, and once a lesion occurs, a number of degenerative events follow, such as the shrinkage of axons and associated neural structures, and the consequent actions of glial cells in repairing the damage as much as possible. Despite these changes, some recovery of function via restitution and/or substitution mechanisms occurs, however, for more severe injuries deficits often persist. Moderate and severe TBI during childhood results in specific attention and information processing deficits up to 24 months postinjury. Not all areas of attention are affected similarly, with factors including the nature of the task (e.g., visuo-motor tasks in comparison to computerized reaction time tasks), task complexity, and speed requirements affecting outcome. Results provide partial support for findings from the adult literature where deficits for speed of processing are reported (Murray et al., 1992; Ponsford & Kinsella, 1992). However, while adult TBI is thought to cause a general disruption to attention and information processing (Van Zomeren & Brouwer, 1994), this current study revealed that deficits seen following severe TBI are not generalized, with simple motor speed relatively intact (inconsistent with Anderson & Fenwick, 1998; Anderson & Pentland, 1998), and visuo-motor processing more impaired, suggesting that speed of processing deficits may be more evident for more complex and multidetermined tasks. In contrast to adult findings, evidence for impairments in sustained attention was also found in our child sample. These deficits were most evident following severe TBI, and may reflect developmental characteristics of the group, that is, that sustained attention is immature at the time of the injury (McKay et al., 1994) and so more vulnerable and at a greater risk following childhood TBI.

With respect to selective and shift measures, dose-related deficits were identified, however, it is difficult to separate attentional effects from visuo-motor processing requirements in these domains. Future research may be directed towards more accurate delineation of these skills. The more widespread attentional difficulties seen in childhood TBI may reflect the relatively immature state of the CNS at the time of injury. Thus, attentional skills not developed (e.g., sustained attention and processing speed) may be more vulnerable and less likely to develop normally and so cumulative deficits may also result after TBI in childhood (McKay et al., 1994).

With regard to behavioral measures, results from parent and teacher reports generally indicated that moderate and severe TBI groups did not improve with time since injury, but that in fact there was a higher frequency of maladaptive characteristics that continued to 2 years post-TBI. It may be suggested that these behavioral indices have different recovery profiles to standardized cognitive measures, and that such maladaptive behavior may in fact impede optimal recovery of other skills in the years following TBI.

The ability of this study to comment on absolute impairments for mild TBI is limited by the lack of a control group. However, each TBI group became their own control as performance was compared over time, and this was the main interest of the study. The restricted age range of the participants may also be seen as a limitation in the ability to generalize findings to other age groups; however, there are a number of advantages in using a limited age range in pediatric samples. In particular, it allowed for the same test battery to be administered to all participants at all stages of the study. Further, developmental issues are consistent across the group.

A further potential limitation of the study is the use of parental and teacher recall of preinjury measures in order to establish preinjury functioning. Such an approach, while somewhat controversial, provides an opportunity to document preinjury abilities. While this may result in some biased response patterns from the parent during this traumatic time (e.g., elevating the child's ability), our data do not suggest this, with score distributions on this measure being consistent with those described in the test manual, and overall group means consistent with those documented in other recent Australian samples.

Future studies may include further follow-up of these children to allow for the systematic monitoring of these and other emerging skills, for example, executive skills, as the participants become adolescents and adults. Furthermore, future studies employing systematic MRI scan techniques during the acute period postinjury will ensure that brain pathology is better documented, particularly for the mild TBI group, enabling research to address the association between brain pathology and behavioral function more accurately.

Conclusions

The present study suggests that attentional deficits do occur and persist following TBI, with degree of impairment related to injury severity. Results show minimal impact of injury for children with mild TBI. In contrast, children sustaining a severe TBI perform more slowly on a range of tasks where speed and visuo-motor coordination are critical for test performance. These children also demonstrate impaired sustained attention, with variability of test results reflecting the difficulties in interpreting performances on multidetermined measures. It is important to look closely at measures of attention in order to ascertain whether they are measuring what they pertain to measure, or whether each task is tapping a number of skills, some of which recover more quickly than others following TBI. It has been argued that deficits in attention and speed of processing may impede future learning and acquisition of knowledge, resulting in current and cumulative deficits, and so it is important to gain a better understanding of the recovery of these skills following childhood insult.