Optimization of encoding specificity for the diagnosis of early AD: The RI-48 task

Abstract

The aim of this study was to evaluate the discriminant validity of the RI-48 test, a shorter French version of the Category Cued Recall portion of the Double Memory Test developed initially by Buschke and colleagues (1997), in the diagnosis of mild and very mild Alzheimer disease (AD). The distinctive feature of the RI-48 task is that encoding specificity was increased by adding an immediate cued recall stage at the encoding phase. The results show that the RI-48 task seems to be well adapted to the clinical context and to have good psychometric properties, in particular a lack of a ceiling effect. Moreover, this task appears to be especially well suited for the diagnosis of both mild and very mild AD (sensitivity of 93% and 83.8%). From a more theoretical point of view, this study confirms the importance of optimizing the encoding specificity for the diagnosis of very mild AD, since the more encoding specificity is accentuated, the more discriminating power is increased for the diagnosis of very mild AD.

S. Adam is supported by Grant 98/03–215 of the Government of the French-Language Community of Belgium (Actions de Recherche Concertées).

Notes

¹ These tasks are based on the theoretical principle of “encoding specificity” (Thomson & Tulving, 1970), which postulates that acquisition and retrieval conditions must be coordinated to maximally enhance spontaneous free recall in an episodic memory test (see also Schacter & Tulving, 1982).

² Brown and Storandt used only the category cued recall portion of the DMT (that is, the condition where the same semantic cue is given both at encoding and retrieval) as this was the condition that provided the greatest discriminating power for the diagnosis of dementia.

³ Compared to the 64-CCR task, we preferred to decrease the number of semantic categories rather than the number of items per category. Indeed, as task complexity increases with the cue load, the risk to observing a ceiling effect decreases.

⁴ To illustrate these two subscores, we can, for example, consider the performance of one participant on the RI-48 scale. He had an ICR score of 34/48, and a DCR score of 26/48. Of the 34 words encoded with only one trial in the encoding phase, 22 were recalled in the delayed cued recall phase. The DCRa subscore was therefore equal to .65 (i.e., 22/34). Of the 14 words not recalled at the first trial in the encoding phase, 4 were recalled subsequently in the delayed cued recall phase. Therefore, the DCRb subscore was equal to .29 (i.e., 4/14).

⁵ The discriminant validity of a test is determined by the area under the curve: the larger the area under the curve, the greater the diagnostic power.

Adam, S., Van der Linden, M., Poitrenaud, J., Kalafat, M., et les membres du groupe GRECO Mémoire (2004). L'épreuve de rappel indicé à 48 items (RI-48). In M. Van der Linden, S. Adam, A. Agniel, C. Baisset Mouly, et al. (Eds.), L'évaluation des troubles de la mémoire: Présentation de quatre tests de mémoire épisodique (avec leur étalonnage). Marseille, France: Solal.