EXPRESS: The processing mechanism of mixed prospective memory: Changes in internal and external attention.

Mixed prospective memory (MPM) is a special form of prospective memory (PM) with both time and event clues. Depending on the classification of the time clue clarity, MPM can also be divided into time-period MPM and time-point MPM. MPM and TBPM may have different processing mechanisms due to the additional event clue, and it involves two aspects of attention: internal and external attention. Internal attention is indirectly reflected in ongoing task performance, while external attention is directly reflected in the frequency of checking the time. This study aimed to investigate whether there are differences in the processing mechanisms between TBPM and the two types of MPM. The current study examined the changes in internal and external attention for different types of MPM and TBPM under both free and restricted time monitoring conditions. The results showed that in terms of the PM performance, time-point MPM was the best, followed by time-period MPM, with TBPM as the worst. In the performance of ongoing tasks, the two types of MPM were better than TBPM in some stages but worse than the baseline. In addition, the two MPMs evoked a lower time monitoring frequency than TBPM under different monitoring conditions. These results suggest that, compared with TBPM, MPM reduces both internal and external attention consumption. Internal attention consumption displayed dynamic changes for both types of MPM, and the time-point MPM had higher internal attention effectiveness than the time-period MPM. The dynamic multiprocess theory is supported by these results.