[Truncated abstract] Controlled and automatic processing are broad categories, and how best to measure these constructs and their impact on functioning after mild traumatic brain injury (TBI) remains uncertain. The purpose of this thesis was to examine automatic and controlled processing aspects of attention after mild TBI using the Paced Auditory Serial Addition Task (PASAT) and event-related potentials (ERPs). The PASAT is one of the most frequently used tests to evaluate attentional functioning. It has been demonstrated to be a measure sensitive to both acute and longer-term effects of mild TBI, presumably due to demands for rapid processing and executive attentional control. ERPs provide a noninvasive neurophysiological index of sensory processing and cognitive functions and have demonstrated sensitivity to even minor cognitive dysfunction. The parameters provided by this functional technique may be those most likely to distinguish individuals with mild TBI from controls. Initially, it was hypothesized that successful novice PASAT performance requires the engagement of executive attention to establish novel controlled information processing strategies. Ten individuals who had suffered a mild TBI an average of 15.20 months previously were therefore expected to demonstrate processing abnormalities on the PASAT, relative to 10 healthy matched controls. Although the mild TBI group reported significant intensification of subjective symptoms since their injury, compared to controls, the mild TBI group provided a similar amount of correct PASAT responses. ... In the first experiment a visual search task consisting of an automatic detection and a controlled search condition was developed. In the second experiment the search task was performed concurrently with the PASAT task in a dual-task paradigm. In the mild TBI group, prior failure to establish more efficient forms of information processing with practice was found to significantly interfere with simultaneous performance of the PASAT task and the attention demanding condition of the search task. The pattern of impaired performance was considered to reflect a reduction in processing resources rather than a deficit in resource allocation. Dual-task performance in the control group was not associated with a large interference effect. In general, the results of this thesis suggest that individuals with mild TBI are impaired in their ability to progress from the stage of effortful controlled information processing to a stage of more efficient, automatic processing, and thus suffer a subtle attentional deficit. Following mild TBI, performance levels equivalent to controls may only be achieved with an abnormal expenditure of cognitive effort. As a result of the neuropathologic consequences of injury, individuals who have sustained a mild TBI are less able to benefit from practice, experience difficulty coping with simultaneous performance of secondary task, and are susceptible to distressing subjective symptomatology.
|Publication status||Unpublished - 2007|