Attentional decline plays a major role in cognitive changes with aging. However, which specific aspects of attention contribute to this
decline is as yet little understood. To identify the contributions of various potential sources of age decrements in visual search, we combined
response time measures with lateralized event-related potentials of younger and older adults performing a compound-search task, in which
the target-defining dimension of a pop-out target (color/shape) and the response-critical target feature (vertical/horizontal stripes) varied
independently across trials. Slower responses in older participants were associated with age differences in all analyzed event-related
potentials from perception to response, indicating that behavioral slowing originates from multiple stages within the information-processing
stream. Furthermore, analyses of carry-over effects from one trial to the next revealed repetition facilitation of the target-defining dimension
and of the motor response—originating from preattentive perceptual and motor execution stages, respectively—to be independent of age.
Critically, we demonstrated specific age deficits on intermediate processing stages when intertrial changes required more executively
controlled processes, such as flexible stimulus-response (re-)mapping across trials.