Measuring task structure with transitional response times: Task representations are more than task sets

Dykstra, Tobin; Smith, Derek M.; Schumacher, Eric H.; Hazeltine, Eliot · 2022 · Psychonomic Bulletin & Review

DOI: 10.3758/s13423-021-02035-3

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Summary

This study addresses the limitations of conventional task-switching paradigms, which rely on experimenter-defined categories to measure "switch costs" in cognitive control. The authors argue that this approach assumes a priori knowledge of how stimulus-response (SR) mappings are organized, potentially obscuring the true structure of task representations. To overcome this, Dykstra et al. introduce a novel method using transitional response times (RTs), which analyzes the change in RT based on specific response sequences without predefined task sets. The goal was to determine if this fine-grained approach reveals structural details of task representations that conventional switch cost measures miss. The researchers conducted two experiments involving participants responding to centrally presented stimuli using eight keys on a keyboard. In Experiment 1, 72 participants were assigned to conditions varying by stimulus set (one set of numbers vs. two sets: numbers and faces) and response mode (one-hand vs. two-hand). Experiment 2 involved 36 participants using only face stimuli to replicate the one-set, one-hand condition with arbitrary mappings. The authors analyzed data using both conventional ANOVA for switch costs and a transitional RT approach, where RTs were z-scored and visualized as network graphs using force atlas modeling to depict connectivity between responses. Conventional analysis revealed significant switch costs when responses switched sides (left to right or vice versa), but these costs were unaffected by stimulus set or response mode, suggesting no change in task structure. In contrast, the transitional RT analysis revealed distinct organizational patterns. In conditions with a single stimulus category, responses formed a linear "chain" where neighboring keys on the keyboard had significantly shorter transitional RTs, mirroring the physical layout of the keys. This chain structure persisted in Experiment 2 with face stimuli, though it was weaker. However, when two distinct stimulus categories were used, this neighbor-based chain was broken, and responses clustered by side rather than adjacency. Post hoc analyses confirmed that the benefit of neighboring responses was significant and moderated by stimulus set and response mode. The findings demonstrate that task representations are more complex than simple task sets. The transitional RT approach detected a chain-like organization driven by response proximity in single-set conditions, a structure invisible to conventional switch cost measures. This suggests that switch costs can arise from factors other than switching between distinct task sets, such as the physical configuration of responses. The study concludes that transitional RT analysis provides a more detailed and assumption-free picture of task structure, offering a valuable tool for future research into the neural and behavioral signatures of cognitive control.

Key finding

Transitional response time analysis reveals that single-stimulus-category tasks organize responses into linear chains, a structural pattern undetectable by conventional switch cost measures which showed no effect of stimulus category.

Methodology

lab_experiment

Sample size: 108

Provenance

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Topics

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• task switching