Accumulating evidence about what prospective memory costs actually reveal.

Strickland, Luke; Heathcote, Andrew; Remington, RW; Loft, Shayne · 2017 · Journal of Experimental Psychology Learning Memory and Cognition

DOI: 10.1037/xlm0000400

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Summary

This study investigates the cognitive mechanisms underlying prospective memory (PM) costs, specifically testing whether these costs result from capacity-sharing between tasks or from strategic delays in response selection. PM costs refer to the slowing of response times on an ongoing task when participants must also remember to perform a specific action upon encountering a cue. Competing theories attribute this slowing either to the division of limited cognitive resources (capacity-sharing) or to an increase in the amount of evidence required before responding (delay theory). Previous modeling studies suggested delay theory was more accurate, but those studies used PM tasks that may not have sufficiently demanded shared processing resources. To address this, Strickland et al. employed a lexical decision task where participants determined if letter strings were words or non-words. They introduced two PM conditions: a non-focal condition requiring detection of words belonging to a semantic category (e.g., animals), and a focal condition requiring detection of a single specific target word. The semantic non-focal task was chosen because it likely shares processing resources with lexical decisions more than previous visual-based PM tasks. The authors modeled the data using the Linear Ballistic Accumulator (LBA) and the Diffusion Decision Model (DDM) to separate changes in processing speed (drift rate) from changes in response caution (threshold) and non-decision time. The results showed that PM costs in both focal and non-focal conditions were driven primarily by increases in response thresholds, with no significant decrease in drift rates. This finding supports delay theory, indicating that participants strategically slowed their responses to allow more time for PM retrieval, rather than suffering from reduced processing capacity. Specifically, threshold increases were larger for word trials than non-word trials, suggesting a strategic bias to withhold word responses when PM targets were always words. Additionally, under non-focal conditions, thresholds increased for non-words as well, implying that the perceived complexity of the non-focal task induced a global strategic slowing, whereas the focal task did not. Non-decision time contributed minimally to costs and was less consistent across models. These findings challenge capacity-sharing theories of PM costs, demonstrating that even when PM tasks are designed to overlap significantly with ongoing task processing, the resulting slowdown is strategic rather than resource-based. The study clarifies that PM costs reflect a trade-off where participants prioritize accuracy on the less frequent PM task by increasing response criteria, rather than a depletion of functional cognitive capacity. This distinction is crucial for understanding how prospective memory interacts with concurrent cognitive processes.

Key finding

Prospective memory costs are caused by strategic increases in response thresholds rather than reduced processing speed or capacity-sharing.

Methodology

lab_experiment

Sample size: 35

Provenance

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Topics

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• prospective memory interruptions