Task complexity and signal detection analyses of lexical decision performance in Alzheimer's disease

This experiment addressed the issue of whether the changes in semantic memo ry performance associated with Alzheimer's disease (AD) could be distinguis hed from a generalized cognitive slowing. Young adults, healthy older adult s, and AD patients performed 3 different reaction time (RT) tasks involving yes-no responses to visually presented letter strings. Task complexity ana lyses indicated that performance in the semantic task (lexical decision) wa s consistent with a generalized slowing of cognitive function that was grea ter in magnitude for AD than for normal aging. Signal detection analyses of the lexical decision data demonstrated AD-related changes in word-nonword discrimination, response bias, and the relation between discrimination and RT. The general cognitive slowing associated with AD was accompanied by add itional changes specific to the performance of this semantic memory task.