THE EFFECTS OF CLOSED-HEAD INJURY, SENILE DEMENTIA OF THE ALZHEIMERS TYPE, AND PARKINSONS-DISEASE ON COVERT ORIENTATION OF VISUAL-ATTENTION

Covert orientation of visual attention was studied in four clinical gr oups: mild closed head injury (CHI mild), moderate to severe closed he ad injury (CHI mod/severe), dementia of the Alzheimer type (DAT), and Parkinson's disease (PD). Subjects rapidly pressed a button in respons e to one of two lateral peripheral targets. The target was preceded by a central cue that was either neutral, valid or invalid with respect to target location. A NoGo cue indicated that no response should be ma de. Whereas the normal control subjects of all age groups showed a ben efit in reaction time (RT) to targets in expected locations and a RT c ost when targets occurred in the unexpected side of space, both CHI gr oups showed reduced or no benefit but a normal cost. The PD group show ed a reduced cost but normal benefit, and the DAT group were faster in response to targets after valid than invalid cues, but slowest to neu trally cued targets. Analysis of the amplitude of the contingent negat ive variation (CNV) and the amplitude and latency of the P3 related to targets supported the implication that different mechanisms of visual attention are impaired in these groups with different brain disorders . In the CHI groups, the focusing of attention during the cue-target i nterval was impaired. In DAT, division of attention was compromised, a nd in PD there was poor maintenance of attention. The impairments may be attributed to dysfunction of the distributed brain regions of the c ortico-cortical network subserving visual spatial attention.