Recent developments in the study of information processing suggest that multiple memory systems may exist. One implication of this suggestion is that different kinds of memory may be differentially affected by age. For example, acquisition of the "implicit" knowledge, which does not require conscious evaluation of the material to be learned, may be unimpaired as a result of aging, whereas acquisition of explicit knowledge, which requires conscious processing of the material to be learned and effortful attention to the recall of this material may be more affected by the normal aging process. lt has been suggested that classical conditioning is a form of implicit learning, yet it has been found that both EB and electrodermal conditioning are impaired in the elderly. These findings are obviously incompatible with the above implication that implicit learning is relatively unaffected by age. However important control experiments were not employed in these previous studies, making it impossible to determine whether the age-related deficits obtained were due to acquisition or performance impairments. It is also possible that some types of implicit learning may be more affected by aging than others. To assess these alternatives we plan to study both eyeblink and heart rate conditioned responses in human subjects as a function of age and to control for age-related differences in performance. We will also determine whether the performance of subjects of different ages on classical conditioning tasks are related to tests of cognitive function that have been previously used to differentiate between explicit and implicit knowledge.