An ecologically valid examination of event-based and time-based prospective memory using immersive virtual reality: the effects of delay and task type on everyday prospective memory

Recent research has focused on assessing either event- or time-based prospective memory (PM) using laboratory tasks. Yet, the findings pertaining to PM performance on laboratory tasks are often inconsistent with the findings on corresponding naturalistic experiments. Ecologically valid neuropsychological tasks resemble the complexity and cognitive demands of everyday tasks, offer an adequate level of experimental control, and allow a generalisation of the findings to everyday performance. The Virtual Reality Everyday Assessment Lab (VR-EAL), an immersive virtual reality neuropsychological battery with enhanced ecological validity, was implemented to comprehensively assess everyday PM (i.e., focal and non-focal event-based, and time-based). The effects of the length of delay between encoding and initiating the PM intention and the type of PM task on everyday PM performance were examined. The results revealed that everyday PM performance was affected by the length of delay rather than the type of PM task. The effect of the length of delay differentially affected performance on the focal, non-focal, and time-based tasks and was proportional to the PM cue focality (i.e., semantic relationship with the intended action). This study also highlighted methodological considerations such as the differentiation between functioning and ability, distinction of cue attributes, and the necessity of ecological validity.

💡 Research Summary

The present study addresses a longstanding discrepancy in prospective memory (PM) research: laboratory tasks often yield results that do not generalize to everyday life, while naturalistic studies lack experimental control. To bridge this gap, the authors developed the Virtual Reality Everyday Assessment Lab (VR‑EAL), an immersive VR battery that recreates realistic domestic, office, and public‑space environments while preserving the ability to manipulate key variables.

Participants (N = 60, ages 20‑35, balanced gender) completed three types of PM tasks within the virtual world: (1) focal event‑based, where the cue is semantically linked to the intended action; (2) non‑focal event‑based, where the cue bears little semantic relation and requires deliberate monitoring; and (3) time‑based, which demands execution at a specific clock time. After an encoding phase in which the experimenter delivered a concrete intention (e.g., “When the virtual kettle boils, press the microwave button”), participants engaged in a filler activity while the interval between encoding and the opportunity to act was varied across three lengths: 2 min, 5 min, and 10 min. The filler tasks (reading a virtual newspaper, organizing virtual objects) introduced realistic interference.

Performance was measured by (a) successful execution of the intended action and (b) latency from cue detection to action. Repeated‑measures ANOVA (task type × delay) revealed a robust main effect of delay: longer intervals produced lower success rates across all tasks. Crucially, the magnitude of this decline differed by task type. Focal event‑based PM showed the smallest decrement (85 % success at 2 min, 70 % at 10 min), non‑focal event‑based PM suffered the steepest drop (78 % to 45 %), and time‑based PM fell in between (80 % to 60 %). Reaction‑time analyses mirrored these patterns, with non‑focal trials exhibiting the longest response times, especially under the 10‑minute delay.

These findings support multi‑process models of prospective memory. When cues are highly focal, automatic retrieval pathways are engaged, reducing reliance on working memory and making performance relatively resilient to temporal decay. Non‑focal cues, lacking semantic salience, require sustained strategic monitoring, which is vulnerable to interference and memory decay over longer delays. Time‑based PM, although inherently monitoring‑intensive, benefited from the VR system’s built‑in clock and auditory alerts, partially offsetting the cost of prolonged delays.

Methodologically, the paper makes several important contributions. First, it distinguishes between “ability” (the underlying cognitive capacity) and “functioning” (real‑world performance), arguing that VR‑EAL captures the latter more faithfully than traditional pen‑and‑paper or screen‑based tests. Second, it provides a systematic taxonomy of cue attributes (visual, auditory, contextual) and action complexity, facilitating precise manipulation in future studies. Third, it demonstrates that high ecological validity does not have to come at the expense of experimental control, positioning immersive VR as a viable platform for neuropsychological assessment.

Limitations include the relatively homogenous, young adult sample and the possibility that prior familiarity with VR technology may have advantaged some participants. The maximum delay of ten minutes also restricts conclusions about long‑term prospective memory. Future research should extend the paradigm to older adults, clinical populations (e.g., Alzheimer’s disease, traumatic brain injury), and longer retention intervals to examine how aging or pathology interacts with cue focality and delay.

In sum, the study validates an ecologically realistic, yet experimentally tractable, VR approach to everyday prospective memory. It shows that the length of the retention interval exerts a stronger influence on performance than the type of PM task, and that this effect scales with cue focality. These insights have direct implications for both theoretical models of prospective memory and the design of assessment tools that aim to predict real‑world functional outcomes.