The concurrent validity of critical flicker fusion threshold (CFFT) and flicker threshold measurement was examined in 23 female and three male patients with primary degenerative dementia of the Alzheimer type (PDDAT). Patients had a mean age of 8 1.7 6.05 years (range 67-89). Diagnosis of PDDAT was based on the DSM-111-R classification. Both the CFFT and flicker thresholds were found to be highly and significantly correlated with standardized clinical assessment (Global Deterioration Scale), cognitive function (Abbreviated Mental Test) and psychomotor performance (Choice Reaction Time). The implications of these two measures for clinical trial research and the longitudinal assessment of patients with Alzheimer's disease are discussed.
KEY woms-Critical flicker fusion threshold, primary degenerative dementia of the Alzheimer's type, concurrent validity.
Alzheimer's disease affects the individual, the family and society. Because of its prevalence in very old people and the age structure of the population, it represents an increasing economic burden. Clinical trials in dementia are expensive, time-consuming and, to date, not very successful. Despite the wide range of potential drugs available, Byrne and Arie (1990) noted 'the time has not yet come to use these drugs other than as part of carefully designed research'. Although there are standardized diagnostic criteria (NINCDS-ADRA, DSM-111-R, etc) there is little agreement on which psychometric measures are the most valid and reliable for clinical evaluation of change. These and other differences between clinical trials make it difficult to compare different studies. It is therefore import-C:orrespondciice to first author. ant to have standardized, reliable and valid measures to assess new pharmaceutical compounds.
Critical flicker fusion threshold (CFFT) has been widely used in psychopharmacology for the past 30 years to evaluate psychotropic drugs including antidepressants, anxiolytics and nootropic drugs. However, most of these studies have been performed on young and elderly volunteers (Simonson