Characterising monitoring processes in event-based prospective memory: Evidence from pupillometry

Moyes, Joseph; Sari-Sarraf, Nadia; Gilbert, Sam J. · 2018 · OpenAlex-citations

DOI: 10.1016/j.cognition.2018.12.007

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Summary

This study investigates the cognitive mechanisms underlying event-based prospective memory (EBPM), specifically addressing the debate between sustained monitoring and transient checking processes. In EBPM tasks, participants perform an ongoing activity while maintaining an intention to respond to specific cues. A common finding is the "PM cost," where response times on non-target trials are slowed when a prospective intention is active. Theoretical accounts suggest this cost arises from either a sustained "retrieval mode" maintained throughout the task or a transient "checking" process triggered by each stimulus. Because behavioral measures cannot distinguish processes occurring in the gaps between trials, the authors employed pupillometry to measure continuous cognitive load. They hypothesized that sustained monitoring would produce a constant increase in pupil diameter, whereas transient checking would yield time-locked pupillary responses aligned with stimulus presentation. The researchers conducted two experiments using a lexical decision task with three conditions: ongoing-only, single-item PM (focal, requiring detection of a specific word), and category PM (nonfocal, requiring detection of words belonging to a semantic category). Pupil diameter was recorded continuously using an eye tracker. To isolate monitoring processes from target detection, the analysis focused exclusively on trials preceding the presentation of any PM targets within each block. This design allowed the authors to detect intention-related processing unconfounded by the act of responding to a cue. The experimental design included counterbalanced block orders and matched target frequencies to control for order effects and carryover influences. Behavioral results confirmed the presence of a PM cost in both single-item and category conditions, with significantly greater slowing observed in the category condition. Pupillometric analysis revealed that pupil size was significantly larger in the category PM condition compared to the ongoing-only baseline, but not significantly different from the single-item condition. Crucially, the increase in pupil diameter in the category condition was sustained throughout the trial duration rather than fluctuating in time-locked patterns associated with stimulus onset. There was no significant interaction between condition and time bins, indicating an absence of transient pupillometric signatures for checking non-targets. However, strong transient pupillary responses were observed when actual targets were presented, confirming the sensitivity of the measure to target detection. These findings provide empirical evidence for a sustained monitoring process in EBPM, particularly in nonfocal tasks where semantic categorization is required. The sustained pupillary dilation suggests that cognitive resources are continuously allocated to maintain the prospective intention, even during inter-trial intervals where no stimulus is present. This supports the multiprocess theory of EBPM, which posits that nonfocal tasks rely on top-down monitoring rather than spontaneous retrieval. By demonstrating that monitoring persists in the gaps between trials, the study clarifies the nature of the PM cost and offers a physiological marker for prospective memory maintenance, distinguishing it from transient, stimulus-driven checking processes.

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• prospective memory interruptions