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Abstract. A common observation in dual tasking is a performance decrement in one or both tasks compared with single tasking. Besides, more specific interference occurs depending on certain characteristics of the two tasks. In particular, even Task 1 performance is often improved when responses in both tasks are compatible (e.g., both require left responses) compared to when they are incompatible: the compatibility-based backward crosstalk effect (BCE). Similar to what is observed for conflict tasks, the BCE is sequentially modulated: It is larger following compatible than following incompatible trials. Previous work has attributed this observation to adaptation effects triggered by response conflict arising during incompatible trials. In two experiments, we assessed sequential modulations following trials with different degrees of such a response conflict. In contrast to our expectations, a clear and sizeable sequential modulation was observed even under conditions where no BCE, and thus no empirical sign of an objective response conflict, was present in the previous trial. Therefore, our results show sequential modulations even without prior response conflict, which is not the (sole) trigger of sequential modulations accordingly. We discuss these results with regard to other potential triggers such as the subjective experience of conflict or difficulty, episodic retrieval, and repetitions of response combinations.

A common explanation for processing limitations in dual-tasking is the existence of a bottleneck during response selection, meaning that the selection of responses can only occur serially for different tasks. However, a large body of data shows that features of a (secondary) Task 2 can already influence the processing of a (primary) Task 1. Such effects are referred to as backward crosstalk effects (BCEs). In the present study, two types of such BCEs were investigated: the compatibility-based BCE, which depends on the dimensional (often spatial) overlap between task features, and a BCE based on a go/no-go task in Task 2 (no-go BCE). Joining a line of research that suggests different mechanisms for these two types of BCEs, we investigated them using a mouse tracking setup. Time continuous analyses revealed that the compatibility-based BCE triggered a spatial activation of the Task 2 response early during Task 1 processing, whereas the no-go BCE triggered an inhibitory effect in the case of a no-go Task 2, which spills over to Task 1 execution. This occurred, however, earlier in the time-course than expected. The results are discussed with regard to recent models of dual-task processing.

According to ideomotor theory, we select actions by recalling and anticipating their sensory consequences, that is, their action effects. Compelling evidence for this theory comes from response–effect compatibility (REC) experiments, in which a response produces an effect with which it is either compatible or incompatible. For example, pressing a left/right response key is faster if it is predictably followed by an action effect on the same, compatible side compared with the other, incompatible side, even though the effect itself appears only after response time is measured. Recent studies investigated this effect with continuous responses (i.e., computer mouse movements) and reported an REC effect in a forced-choice but not in a free-choice task. From the keypressing literature, the opposite result pattern or no differences would have been expected. To clarify this issue, we report 3 experiments with mouse movement responses. Experiment 1 used a simpler scenario than in prior studies and found a similar result: The REC effect was evident in a forced- but not in a free-choice task. Also, sequential modulations of the REC effect were exploratorily analyzed and replicated with higher power in Experiment 2. However, Experiment 3 demonstrated that at least part of the REC effect with mouse movements can be attributed to stimulus–response compatibility (SRC), with a much smaller compatibility effect evident with a procedure for which SRC was reduced. We conclude that a sequentially modulated compatibility effect can be observed with mouse movements, but previous studies may have underestimated the contribution from SRC. The results are also discussed in terms of why the compatibility effect was observed in forced- but not free-choice tasks with mouse movement responses.

Action choices are influenced by future and recent past action states. For example, when performing two actions in succession, response times (RT) to initiate the second action are reduced when the same hand is used. These findings suggest the existence of effector-specific processing for action selection. However, given that each hand is primarily controlled by the contralateral hemisphere, the RT benefit might actually reflect body side or hemisphere-specific rather than effector-specific repetition effects. Here, participants performed two consecutive movements, each with a hand or a foot, in one of two directions. Direction was specified in an egocentric reference frame (inward, outward) or in an allocentric reference frame (left, right). Successive actions were initiated faster when the same limb (e.g., left hand - left hand), but not when the other limb of the same body side (e.g., left foot - left hand) executed the second action. The same-limb advantage was evident even when the two movements involved different directions, whether specified egocentrically or allocentrically. Corroborating evidence from computational modeling lends support to the claim that repetition effects in action selection reflect persistent changes in baseline activity within neural populations that encode effector-specific action plans.