The growing incidence of DAT in our society and the emerging therapeutic advances increases the need for brief and efficient approaches to early diagnosis. Neuropsychological approaches to early diagnosis have been a focus of interest, but some of the published protocols do not rely on demonstrated neurocognitive systems that are now known to be affected in the pre-clinical and early stages of DAT (Chiu et al., 2004; Mundt et al., 2000; Schneider & Levenson, 2002).
The OPAT was shown in the current study to be highly sensitive to the cognitive decline characteristic of the transitional phase to DAT, consistent with previous research. These results strongly support the inclusion of an object-place association paradigm in the general screening procedure for memory difficulties associated with DAT. Not only does the OPAT rely on demonstrated neurocognitive systems affected early in the disease progression, its qualities make it very practical and simple to use. The procedure can be administered within a few minutes, an important feature of screening procedures in the very busy clinical setting, and requires minimal expertise to administer and score. Importantly, performance in the OPAT is unlikely to be influenced by levels of education, cultural background or socio-economic class, and it is well tolerated by the aging population.
The results regarding the clock-anomalies detection paradigm in early detection are less consistent and require further investigation. Consistent with the expectation, detection of clock-anomalies did not distinguish between the groups in this study. The patients' performance in the traditional Clock-Drawing test during the routine neuropsychological examination was, however, mostly impaired. This pattern is conflicting with the suggestion that a semantic-conceptual dimension underlies impaired performance on the CDT (Saling et al., 2002), and suggests that further studies are needed to provide a better understanding of clock-related semantics in early DAT. Nevertheless, the valid clocks section of the CADT highly distinguished between the groups and further development of this approach will determine its applicability and value in the screening procedure.
The present study provides some important directions for future research. First, further investigation of the Object-Place Association paradigm will establish the extent to which forgetting object-place associations interacts with forgetting the objects or the locations themselves. Second, there is a need to further examine the finding that not only the acquisition of the object-place associations occurs slower, it also eliminates quicker in DAT patients. This was not directly investigated in this study but can nevertheless found to be an additional marker of the early stages of dementia. Third, it is proposed here that in early DAT, the breakdown in semantic ability manifests itself first as an increasing difficulty in identifying valid examples of a category due to a strong reliance on prototypical appearance. Only with the progression of this breakdown do patients lose their ability to detect anomalies in invalid instances of a category. Further studies are expected to evaluate this possibility.
In summary, the present investigation demonstrated that a desktop version of the Object-Place Association paradigm and classification of valid clocks to be sensitive markers reflecting the transitional phase between normal aging and DAT. Consistent with previous reports, DAT patients were found to perform poorly on forming arbitrary object-place associations, and on a delayed retrieval of these associations. While they were as able as normal controls to detect anomalies in clock faces, they showed significant impairment in their ability to correctly identify examples of valid clocks. With the growing need for brief and efficient techniques for early detection of DAT, these tasks can prove to be valuable tools in routine neuropsychological screening due to their reliance on impaired neurocognitive systems and their brief, simple and non-threatening nature.