Deficits in visual attention after mild and severe traumatic brain injuries

A whole report paradigm was used to quantify three different components of attention related to visual processing capacity: perceptual threshold, processing speed, and working memory (WM) storage capacity in patients with traumatic brain injury (TBI). The subjects sample was composed of 25 patients with mild TBI (mTBI), 23 patients with severe TBI (sTBI), and 24 matched healthy control subjects. Patient groups were assigned according to the Glasgow Coma Scale. Patients of the mTBI group presented intracranial lesions (termed complicated mTBI). Bundesen’s theory of visual attention (TVA; Bundesen, 1990, 1998) served as a theoretical framework for the analysis of the results. Results indicated augmented perceptual thresholds, as well as impairment in processing speed and WM storage capacity in sTBI, while mTBI showed solely deficits in processing speed. WM storage capacity was associated with trauma severity. The probable importance of white matter connectivity on these impaired parameters is discussed. Through the use of a partial report task, visual selective attention was assessed in 23 patients with mild traumatic brain injury (mTBI), and 23 patients with severe TBI (sTBI). Patient groups were assigned according to the Glasgow Coma Scale (GCS). Based on Bundesen’s theory of visual attention (TVA; 1990, 1998), two parameters were estimated out of the accuracy data of the task performance: top-down control of attentional selection (parameter α), representing task-related attentional weighting for prioritizing relevant visual stimuli, and spatial distribution of attentional weights across both hemifields (parameter wlat). Compared to the task performance of 23 healthy matched control subjects, sTBI patients displayed significantly reduced efficiency of top-down control selection and a pathological imbalance of spatial attentional weighting across hemifields. The performance of mTBI patients was intact in these measures. Parameter α was correlated with the GCS score. On the basis of the literature on clinical TVA-based assessment, the impact of very large lesion types (e.g., contusions) on impaired top-down control as well as the role of an interhemispheric imbalance on the unbalanced attentional weighting in the sTBI group are discussed. In combination with Bundesen’s theory of visual attention (1990, 1998), the whole and the partial report of briefly displayed letter arrays provide the estimation of psy-chophysical parameters related to the visual capacity and the attentional weighting of a given participant: visual perceptual threshold, visual processing speed, visual working memory storage capacity, spatial distribution of attention, and top-down control. Two previous studies of this dissertation (study 1 and 2, see chapter 4 and 5) have already demonstrated that patients with traumatic brain injury (TBI) show a decline in all of these parameters. The aim of the present study was to examine whether these parameters are related to other clinical measures in a TBI population, as demonstrated in a study by Finke et al. (2005) in healthy subjects. In a sample of 51 TBI patients (27 patients with mild and 24 patients with severe TBI, as assessed with the Glasgow Coma Scale), the correlation matrix showed correlations that were comparable to those obtained by Finke et al. (2005) for some measures. However, also unexpected associations between TVA parameters and conventional neuropsychological tests were found, indicating that the correlation pattern change in clinical groups when actual deficits are present. These results are discussed in respect to the potential mechanisms leading to these changes in a group of TBI patients