The present study investigated a simple screening procedure for the cognitive difficulties associated with the early stages of DAT. Object-Place Association and the Clock-Anomalies Detection tasks were developed as part of this study on the basis of previous research (Fowler et al., 2002; Saling, Maccuspie-Moore et al., 2002b). The primary objective was to establish whether a group of early DAT patients could be distinguished from a group of matched control subjects. It was hypothesized that the OPAT would distinguish between early DAT patients and a matched control group given that the earliest stages of DAT are characterized by impaired associative memory (Blackwell et al., 2004; Fowler et al., 2002; Swainson et al., 2001). It was further hypothesized that the CADT would be less likely to discriminate between the groups because semantic impairment appears at a later stage than the associative memory impairment (Nagy et al., 1999; Yilmazer-Hanke & Hanke, 1999).
With regard to the first hypothesis, the findings were supportive. DAT patients performed significantly worse than the control group over the first three trials of the acquisition phase of the OPAT and significantly worse on the delayed recall trial. With regard to the second hypothesis, the findings were partially supportive. While the patients did not perform any worse than controls in their overall clock anomalies detection, a tendency to offer explanations limited to the clock face rather than to the conceptual level was noted in the DAT group. Although this difference did not reach significance, the effect size was nevertheless found to be moderate, suggesting that it would be of interest to repeat this comparison with a larger sample. The unexpected finding, however, was that patients performed significantly worse than the control group in their ability to correctly classify valid clocks. The third hypothesis was that the participants could be classified into their original diagnostic groups on the ba sis of their test performances. This hypothesis was confirmed, and all participants were assigned to their original diagnostic group by a combination of associative memory and clock-related semantics.
These findings are discussed below in relation to previous research, and theoretical issues will be addressed. Subsequently, methodological difficulties will be evaluated and finally implications of the current study and suggestions for future research will be discussed.