Visual attention deficits in Alzheimer's disease: Simple versus conjoined feature search

The authors investigated selective attention in patients with Alzheimer's d isease (AD), using a well-known visual search procedure. In simple feature search, the deficit observed in AD patients represented a baseline shift in the median hit reaction time (RT). On the conjoined feature search task, t he median hit RT for AD patients increased disproportionately with increasi ng array size, indicating an additional cognitive impairment on this task. Of particular importance, the cognitive deficit observed in conjunction sea rch was more profound than that predicted on the basis of previous reports of global cognitive slowing in AD. There was some evidence that the perform ance of AD patients improved more than the performance of controls over the duration of the experimental test session. Patients also had more difficul ty in detecting targets on the right side of hemispace and in more peripher al locations.