Three hypotheses were tested in the current study. Firstly, it was
hypothesized that patients with a diagnosis of very early DAT would
perform worse than a matched control group of non-demented individuals
on the Object-Place Association Task (OPAT):
1. On the delayed recall trial of the task, the patient group would be more impaired in their ability to associate the objects with their location.
2. In the acquisition phase, patients would show a slower improvement than the control group, and therefore would require more trials to arrive at a perfect performance.
Secondly, it was hypothesized that the Clock-Anomalies Detection Task (CADT) would not be successful in discriminating between the groups at an early stage of the disease, and therefore that no significant difference would be found between the groups in detection of anomalies. Thirdly, it was hypothesized that participants would be correctly classified into either the patient group or the control group solely on the basis of their performance on the CADT and the OPAT.
Clock-Anomalies Detection Task (CADT)
Consistent with the recently successful demonstration of the Clock-Anomalies Detection task as a strong predictor of membership in a group of mild to moderate dementia (Saling, Maccuspie-Moore et al., 2002b), this study investigated the utility of this task in screening for the earliest end of the dementia spectrum. As semantic processing was suggested to be mediated by temporoparietal structures, it seems reasonable to speculate that at the early stages of AD, when levels of temporoparietal hypometabolism are relatively low, the detection of clock anomalies will not be significantly impaired compared to a group of healthy elderly controls.
Object-Place Association Task
Recent studies have demonstrated the difficulty of DAT patients in forming and maintaining associations between objects placed in arbitrary locations using the computerized PAL task (Blackwell et al., 2004; Fowler et al., 2002). In the current study, a similar desktop version of the PAL task was evaluated, with the aim to reconfirm the value of this paradigm in the earliest stages of AD with the use of a non-computerized version. As some elderly individuals may feel intimidated by computerized tests, the desktop version might be better tolerated by some of these patients.
The Object-Place Association Task (OPAT) developed for this study measures the ability to form arbitrary associations between every-day objects and boxes located on a small board in which they are hidden. The task was administered with both an acquisition phase, and a delayed recall trial. These tasks rely on a demonstrated relationship with specific neurocognitive systems affected in early DAT. Further, the OPAT and CADT can be administered within a few minutes, with minimal professional knowledge, and are non-threatening. These features emphasize their potential value in clinical settings.