Exploring the Influence of Temporal Factors on Age Differences in Working Memory Dual Task Costs

Working memory is defined by many as the system that allows us to simultaneously store information over brief time periods while engaging in other information processing activities. In a previous study (Rhodes et al., 2019) we found that retention of serially presented letters was disrupted by the introduction of an arithmetic processing task during a 10 second delay period. Importantly, the magnitude of this dual task disruption increased with age from 18 to 81. The demands of each task were adjusted prior to dual task so that age differences did not reflect baseline differences in single task performance. Motivated by these findings, theories of working memory, and additional analyses of processing reaction times from this previous experiment, we report two experiments, using the same tasks and adjustment procedure, attempting to modulate the magnitude of age differences in dual task effects via manipulations focused on time for encoding to-be-remembered material. Providing a delay prior to processing activities, to facilitate switching between the two tasks, did not modulate age differences. Neither did separating the to-be-remembered material temporally, to allow for the creation of more distinct representations. These findings provide two replications of our initial finding and suggest that age differences in working memory dual tasking are not due to limitations in the speed of encoding.