The effect of stimulus availability on task choice in voluntary task switching

Arrington, Catherine M. · 2008 · OpenAlex-citations

DOI: 10.3758/mc.36.5.991

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Summary

This study investigates the factors influencing task selection in voluntary task switching, specifically examining how external stimulus availability interacts with internal preparatory processes. While standard task-switching paradigms measure performance costs, voluntary switching allows researchers to analyze why individuals choose specific tasks. Previous research yielded conflicting conclusions regarding the role of external stimuli: some studies suggested task choice is primarily top-down and goal-directed, while others found strong susceptibility to bottom-up stimulus features. This paper addresses this discrepancy by manipulating the temporal availability of stimuli and the time available for internal preparation. The researchers conducted two experiments using a voluntary task-switching paradigm where participants performed either an even/odd judgment on a digit or a consonant/vowel judgment on a letter. Both stimuli appeared on every trial, but their onset times were varied using stimulus onset asynchrony (SOA) levels of 0, 50, 100, or 150 milliseconds. Experiment 1 established that the probability of performing the task associated with the first-appearing stimulus (S1) increased linearly as the SOA increased, demonstrating that greater stimulus availability drives task choice. Experiment 2 introduced a manipulation of the response–stimulus interval (RSI), comparing short (400 ms) and long (2,000 ms) preparation intervals. This design allowed the authors to test whether internal preparation mitigates the influence of external stimulus timing. The results confirmed that stimulus availability significantly affects task choice, but this effect is modulated by the preparation interval. In Experiment 2, the increase in the probability of choosing the S1-associated task as SOA increased was significantly stronger at the short RSI than at the long RSI. At the short RSI, participants had less time to form an internal task goal before stimuli appeared, making them more reliant on whichever stimulus was available first. Conversely, at the long RSI, participants had sufficient time to establish an internal task set, reducing their dependence on stimulus availability. Additionally, standard switch costs were observed, with reaction times slower on task switches than repetitions, and these costs were larger at the short RSI. These findings reconcile previous conflicting literature by demonstrating that task choice in voluntary switching is driven by both internal, goal-directed processes and external, stimulus-driven factors. The study supports a model where internal preparation reduces the impact of bottom-up influences. Specifically, when internal task goals are established early, they guide attention and task selection regardless of stimulus timing. However, when preparation time is limited, external stimulus availability exerts a stronger influence on behavior. This implies that voluntary behavior in multitask environments is not purely top-down but results from a dynamic interaction between executive control and the immediate stimulus environment.

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• task switching

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• Empirical Findings: behavioral performance data