Severity of cognitive impairment in Alzheimer's disease affects list learning using the California Verbal Learning Test (CVLT)

Impairment in list learning is considered a primary symptom of Alzheimer's disease (AD), yet there are no published reports examining the relationship between list learning and severity of cognitive impairment. We gave nine-item and 16-item versions of the California Verbal Learning Test (CVLT; Delis et al., 1987), a standardized shopping list assessment of memory, to 24 AD patients (mean age = 76.2 +/- 8.1; mean years of education = 13.8 +/- 2.4), who were stratified into four groups based on MMSE scores (mean = 16.0 +/- 5.6). ANOVAs revealed severity effects for total list learning (p < 0.001), the first trial (p < 0.001), the last trial (p < 0.001) and short- and long-delay recall measures. Most of these differences seemed due to floor effects. For example, the modal number of words recalled after a delay was 0 by subjects with MMSE scores below 21. Severity of cognitive impairment was associated with the proportion of intrusions such that the most severely demented subjects gave almost entirely intrusion responses. Surprisingly, list length did not significantly affect any of the free recall measures. Our results suggest that list learning and recall seem to be lost relatively early in AD. Measures of list recall like the CVLT may not be useful in tracking severity of cognitive impairment over time.