ABSTRACT
There are some limitations of this study that require acknowledgment. First, the sample size was small, which may have decreased the power for detecting significant differences. However, given the substantial effects demonstrated through Tukey-adjusted level of significance in post hoc analyses of the RT data, this did not appear to be a major concern. However, the small number of targets (blue words) in Blocks I and 2 certainly limited the types of analyses that could be performed to nonparametric techniques that are less powerful. Here, too, some effects in planned comparisons were strong enough to emerge leaving post hoc analyses to fall victim to limited power. Future experiments will be designed to allow for parametric analyses of behavioral data to overcome this issue. Second, the RT data from Block I was compromised in that a large proportion of participants failed to perform the PM tasks following a relatively brief delay (see Figure I). What is evident from the figure is that the slowed mean RT of Ortho group in Block 1 resulted from 75% of the participants attending for the E-B PM cue whereas the Mild TBI group appeared equal or superior to the Orthos as only 25% of the group actually was engaged in the PM task. Once the reminder was given, the upward trend in RT is clear in the Mild TBI group as the majority of the group was once again engaged in the PM task. Third, the participants were released from the PM task at the end of the experiment, which could have inflated the difference in RT between the PM versus no-PM conditions; practice effects of performing the decision task could have accrued so that Block 3 was much quicker than if a no-PM condition had preceded the PM condition. Such an effect would be most evident in the Severe TBI group because adults with severe TBI have been shown to have a longer and slower practice effect trajectory in RT measures (Schweinberger, Buse, & Sommer, 1993), which would have resulted in a downward trajectory up to block 4 when the reminder occurred. This also does not necessarily appear to be the case as the Severe TBI group appears to have reached a RT plateau by block 3 and remained stable through block 4 as depicted in Figure 2.
