A preliminary study of the validity of memory tests recommended by the Working Group for individuals with moderate to severe intellectual disability

Normal aging and Dementia of Alzheimer's Type (DAT) among higher functioning individuals with intellectual disability (ID) have been relatively well studied using a variety of cognitive tests. However, cognitive studies for lower functioning individuals with ID are scarce in the literature. The Working Group recommended the Test Battery for the Diagnosis of Dementia in Individuals with various level of ID. Few studies have investigated whether the Test Battery is useful to study dementia among individuals with moderate to severe ID. The purpose of this study is to investigate whether the memory subtests of the Test Battery are useful for measuring memory function and studying DAT in individuals with moderate to severe ID.

We compared performances on the memory subtests in the Test Battery between 31 normal controls and 13 DAT patients with moderate to severe ID. Performance on the Picture Recognition Test was also compared between five normal controls and five DAT patients. This test was designed by our team to measure memory functions of individuals with moderate to severe ID.

Among the memory subtests of the Test Battery, the Autobiographical Memory and the Orientation were found to be useful for studying normal and abnormal aging among individuals with moderate to severe ID. Preliminary data for the Picture Recognition Test demonstrated that these individuals properly responded to this test and the majority of DAT patients could be differentiated from the normal controls based on their performance.

Further studies are necessary to improve usefulness of the memory subtests of the Test Battery for lower functioning individuals with ID. While the results suggest that the Picture Recognition Test may be more effective in discriminating individuals with DAT, given the very small sample sizes, a study with larger sample sizes should be undertaken to validate these findings.