Spoken word recognition in individuals with dementia of the Alzheimer's type: Changes in talker normalization and lexical discrimination

Four experiments were conducted to examine the effects of dementia of the Alzheimer's type (DAT) on talker normalization and lexical discrimination. Talker normalization has been proposed as the principal mechanism underlying listeners' ability to maintain perceptual constancy for speech signals. Lexical discrimination refers to the ability to distinguish individual words from phonetically similar items stored in the mental lexicon. Healthy older adults served as controls. Comparisons of controls and very mildly impaired patients with DAT revealed no significant change in either lexical discrimination or talker normalization. In contrast, individuals with more advanced DAT (mildly demented) exhibited significant declines in both abilities. The results are discussed with respect to the possible roles of general slowing and inhibitory declines as factors affecting speech perception in DAT.