The role of task-related learned representations in explaining asymmetries in task switching

Abstract

Task switch costs often show an asymmetry, with switch costs being larger when switching from a difficult task to an easier task. This asymmetry has been explained by difficult tasks being represented more strongly and consequently requiring more inhibition prior to switching to the easier task. The present study shows that switch cost asymmetries observed in arithmetic tasks (addition vs. subtraction) do not depend on task difficulty: Switch costs of similar magnitudes were obtained when participants were presented with unsolvable pseudo-equations that did not differ in task difficulty. Further experiments showed that neither task switch costs nor switch cost asymmetries were due to perceptual factors (e.g., perceptual priming effects). These findings suggest that asymmetrical switch costs can be brought about by the association of some tasks with greater difficulty than others. Moreover, the finding that asymmetrical switch costs were observed (1) in the absence of a task switch proper and (2) without differences in task difficulty, suggests that present theories of task switch costs and switch cost asymmetries are in important ways incomplete and need to be modified.

Figure 1. An illustration of the arithmetic switch tasks with solvable and pseudo equations.

A. Trials of the arithmetic and symbol-switching task (Experiment 1). For the arithmetic task, participants had to solve equations and indicate whether the answer was correct, while for the symbol-switching task participants had to indicate the type of operation. B. Trials involving pseudo equations of the symbol-switch letter task where participants had to indicate type of operation (Experiment 2).

Figure 2. Switch-costs for the arithmetic- and symbol switch task.

Reaction time switch costs (computed as RT repeat – RT switch) for Experiment 1, depicted separately for trials that required switching to additions/‘+’ and subtractions/‘−’ and for the arithmetic-switching task (Arithmetic) versus the symbol-switching task (Symbol). Error bars depict the Standard Error of the Mean Difference between repeated and switched trials , .

Figure 3. Switch costs for symbol-switch tasks.

Reaction time switch costs (computed as RT repeat – RT switch) for A. the symbol-switching task using numbers equations (Numbers; from Experiment 1) and letter equations (Letters), and B. the symbol-switching task using only letter equations when stimulus presentation is fixed at 2.5 seconds (Fixed) and when stimuli are offset upon motor response (Stimulus offset), from Experiment 2. Error bars depict the Standard Error of the Mean Difference between repeated and switched trials , .

Figure 4. Switch costs for symbols type and size.

Switch costs in the mean reaction times (RTs) for Experiment 3, depicted separately for small and big single-line symbols and two-lines crossed symbols when only the size switched, only the symbol switched, or both the size and symbol switched (computed as RT on repeat trials – RT on switch trials). Error bars depict the Standard Error of the Mean Difference between repeated and switched trials , .