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

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.10 page(s

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

<p>Reaction time switch costs (computed as RT repeat – RT switch) for <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0061729#s2" target="_blank">Experiment 1</a>, 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 <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0061729#pone.0061729-Franz1" target="_blank">[66]</a>, <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0061729#pone.0061729-Pfister1" target="_blank">[67]</a>.</p

Mean reaction times (RTs; in ms) followed by the Standard Error of the Mean (<i>SEM</i>) and mean proportion of errors (ERR, in %) followed by standard deviation (<i>SD</i>) for same and switched addition (+) and subtraction (−) conditions, listed separately for the arithmetic task and the symbol-identification task of Experiment 1.

<p>Mean reaction times (RTs; in ms) followed by the Standard Error of the Mean (<i>SEM</i>) and mean proportion of errors (ERR, in %) followed by standard deviation (<i>SD</i>) for same and switched addition (+) and subtraction (−) conditions, listed separately for the arithmetic task and the symbol-identification task of <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0061729#s2" target="_blank">Experiment 1</a>.</p

Mean reaction times (RTs, in ms) followed by the Standard Error of the Mean (<i>SEM</i>) and mean proportion of errors (ERR) followed by standard deviation (<i>SD</i>), for big and small single line or two crossed line stimuli, depicted separately for no switch (Same), switched size, switched symbol and size and symbol switched conditions of Experiment 3.

<p>Mean reaction times (RTs, in ms) followed by the Standard Error of the Mean (<i>SEM</i>) and mean proportion of errors (ERR) followed by standard deviation (<i>SD</i>), for big and small single line or two crossed line stimuli, depicted separately for no switch (Same), switched size, switched symbol and size and symbol switched conditions of <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0061729#s4" target="_blank">Experiment 3</a>.</p

Switch costs for symbol-switch tasks.

<p>Reaction time switch costs (computed as RT repeat – RT switch) for <b>A</b>. the symbol-switching task using numbers equations (Numbers; from <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0061729#s2" target="_blank">Experiment 1</a>) and letter equations (Letters), and <b>B</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 <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0061729#s3" target="_blank">Experiment 2</a>. Error bars depict the Standard Error of the Mean Difference between repeated and switched trials <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0061729#pone.0061729-Franz1" target="_blank">[66]</a>, <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0061729#pone.0061729-Pfister1" target="_blank">[67]</a>.</p