When two actions are easier than one: how inhibitory control demands affect response processing

Erroneous saccade co-execution during manual action control is independent of oculomotor stimulus-response translation ease

Recent multiple action control studies have demonstrated difficulties with single-action (vs. dual-action) execution when accompanied by the requirement to inhibit a prepotent additional response (e.g., a highly automatic eye movement). Such a dual-action performance benefit is typically characterized by frequent false-positive executions of the currently unwarranted response. Here, we investigated whether the frequency of false-positive saccades is affected by the ease of translating a stimulus into a spatial oculomotor response (S-R translation ease): Is it harder to inhibit a saccade that is more automatically triggered via the stimulus? Participants switched on a trial-by-trial basis between executing a single saccade, a single manual button press, and a saccadic-manual dual action in response to a single visual stimulus. Importantly, we employed three different stimulus modes that varied in oculomotor S-R translation ease (peripheral square > central arrow > central shape). The hierarchy of S-R translation ease was reflected by increasing saccade and manual reaction times. Critically, however, the frequency of false-positive saccades in single manual trials was not substantially affected by the stimulus mode. Our results rule out explanations related to limited capacity sharing (between inhibitory control and S-R translation demands) as well as accounts related to the time available for the completion of saccade inhibition. Instead, the findings suggest that the erroneous co-activation of the oculomotor system was elicited by the mere execution of a (frequently associated) manual response (action-based co-activation).

Flipping the script: Action-plan modification during single- and multiple-action control

In this paper, we tested the idea that local changes in action demands (e.g., due to an invalid cue or trial-by-trial) result in frugal modifications of existing action plans via action-plan-modification operations. We implemented an experimental procedure making use of a cue that indicates the action requirements for an upcoming signal with a certain degree of reliability. Crucially, incongruent cue-stimulus pairs either require action-plan modification or "resetting" the prepared action plan and reselecting a new response from scratch. We systematically varied the proportion of valid cues over four experiments. There were four most basic response conditions: left button press, right button press, dual button presses, no action. Results support the concept of action-plan modification rather than reset-reselect: switching between a left and a right response was faster and less error-prone than any other type of switch, both between trials and between cue and signal. Thus, it appears that given two responses that can be conceived of as polar opposites (within the same single-action category), there is an action-plan-modification operation ("invert") that transforms one into the other at a comparatively low cost. Furthermore, we observed a mixed pattern of dual-action costs and benefits. This indicates that participants represented dual actions holistically, that is, not based on a conjunction of single-action plans as building blocks. In addition, switching from null actions to overt actions appeared to require very similar action-plan-modification operations as other types of switches - thus, null actions are apparently not coded as empty sets, but rather represent actions in their own right. Finally, we observed strikingly similar patterns of results for trial-by-trial changes in action demands and intra-trial cue-signal incongruency. This implies that the mere cue-based formulation of an action plan - which is not actually executed - is sufficient to produce action-switching-like effects.

Dual-Action Costs and Benefits in a Uni-Modal Single-Onset Paradigm

While performing two actions at the same time has mostly been associated with reduced performance, several recent studies have observed the opposite effect, that is, dual-action benefits. Previous evidence suggests that dual-action benefits result from single-action inhibitory costs - more specifically, it appears that under certain circumstances, single-action representations are derived from dual-action representations by removing (i.e., inhibiting) one of the component actions. In the present paper, we investigated if this is tied to the presence of multi-modal response demands (i.e., responses making use of two different effector systems). We implemented a very simple experimental paradigm where participants responded to a single stimulus with zero, one, or two uni-modal responses. As predicted, we did not observe dual-action benefits, but rather significant dual-action costs. Furthermore, a trial-by-trial sequence analysis revealed that alternations between both single-action responses were associated with significantly better performance than all other types of action switches. This can be accounted for by assuming that actions are represented as "feature bundles" and that switching a single, binary distinctive feature of an action to its opposite is relatively easy.

Dual-action benefits: global (action-inherent) and local (transient) sources of action prepotency underlying inhibition failures in multiple action control

Previous research has shown that the simultaneous execution of two actions (instead of only one) is not necessarily more difficult but can actually be easier (less error-prone), in particular when executing one action requires the simultaneous inhibition of another action. Corresponding inhibitory demands are particularly challenging when the to-be-inhibited action is highly prepotent (i.e., characterized by a strong urge to be executed). Here, we study a range of important potential sources of such prepotency. Building on a previously established paradigm to elicit dual-action benefits, participants responded to stimuli with single actions (either manual button press or saccade) or dual actions (button press and saccade). Crucially, we compared blocks in which these response demands were randomly intermixed (mixed blocks) with pure blocks involving only one type of response demand. The results highlight the impact of global (action-inherent) sources of action prepotency, as reflected in more pronounced inhibitory failures in saccade vs. manual control, but also more local (transient) sources of influence, as reflected in a greater probability of inhibition failures following trials that required the to-be-inhibited type of action. In addition, sequential analyses revealed that inhibitory control (including its failure) is exerted at the level of response modality representations, not at the level of fully specified response representations. In sum, the study highlights important preconditions and mechanisms underlying the observation of dual-action benefits.

No impact of instructions and feedback on task integration in motor learning

This study examined the effect of instructions and feedback on the integration of two tasks. Task-integration of covarying tasks are thought to help dual-task performance. With complete task integration of covarying dual tasks, a dual task becomes more like a single task and dual-task costs should be reduced as it is no longer conceptualized as a dual task. In the current study we tried to manipulate the extent to which tasks are integrated. We covaried a tracking task with an auditory go/no-go task and tried to manipulate the extent of task-integration by using two different sets of instructions and feedback. A group receiving task-integration promoting instructions and feedback (N = 18) and a group receiving task-separation instructions and feedback (N = 20) trained on a continuous tracking task. The tracking task covaried with the auditory go/no-go reaction time task because high-pitch sounds always occurred 250 ms before turns, which has been demonstrated to foster task integration. The tracking task further contained a repeating segment to investigate implicit learning. Results showed that instructions, feedback, or participants' conceptualization of performing a single task versus a dual task did not significantly affect task integration. However, the covariation manipulation improved performance in both the tracking and the go/no-go task, exceeding performance in non-covarying and single tasks. We concluded that task integration between covarying motor tasks is a robust phenomenon that is not influenced by instructions or feedback.

Ways to Improve Multitasking: Effects of Predictability after Single- and Dual-Task Training

In this study we investigated the effect of predictability on dual-task performance in two experiments. In the first experiment 33 participants separately practiced a continuous tracking task and an auditory reaction time task. Both tasks had a repeating element that made them predictable; in the tracking task this was a repeating segment, and in the auditory task this was an auditory sequence. In addition, one group obtained explicit knowledge about the repeating sequence in the tracking task while the other group trained implicitly. After training, single- and dual-task performance was tested at a post test and retention test. Results showed that predictability only improved performance in the predictable tasks themselves and dual-task costs disappeared for the tracking task. To see whether the task-specific effect of predictability was the results of task prioritization, or because task representations did not have much chance to interact with each other, we conducted a second experiment. Using the same tasks as in Experiment 1, 39 participants now trained both tasks simultaneously. Results largely mirrored those of the first experiment, demonstrating that freed-up resources due to predictability in one task could not be re-invested to improve in the other task. We conclude that predictability has a positive but task-specific effect on dual-task performance.

Effector-Specific Characterization of Brain Dynamics in Manual vs. Oculomotor Go/NoGo Tasks

Motor inhibitory control (IC), the ability to suppress unwanted actions, has been previously shown to rely on domain-general IC processes that are involved in a wide range of IC tasks. Nevertheless, the existence of effector-specific regions and activation patterns that would differentiate manual vs. oculomotor response inhibition remains unknown. In this study, we investigated the brain dynamics supporting these two response effectors with the same IC task paradigm. We examined the behavioral performance and electrophysiological activity in a group of healthy young people (n = 25) with a Go/NoGo task using the index finger for the manual modality and the eyes for the oculomotor modality. By computing topographic analysis of variance, we found significant differences between topographies of scalp recorded potentials of the two response effectors between 250 and 325 ms post-stimulus onset. The source estimations localized this effect within the left precuneus, a part of the superior parietal lobule, showing stronger activity in the oculomotor modality than in the manual modality. Behaviorally, we found a significant positive correlation in response time between the two modalities. Our collective results revealed that while domain-general IC processes would be engaged across different response effectors in the same IC task, effector-specific activation patterns exist. In this case, the stronger activation of the left precuneus likely accounts for the increased demand for visual attentional processes in the oculomotor Go/NoGo task.

Effects of trying 'not to move' instruction on cortical load and concurrent cognitive performance

Motor and cognitive tasks often interfere when performed concurrently. The amount of interference typically scales with difficulty of the tasks involved. Thus, supposedly 'easy' motor tasks with restricted movement amplitude, like sitting on a chair, should show little or no interference with cognitive tasks at all. We measured the processing load induced by different postural tasks and their effect on cognitive performance under cognitive-motor dual-task conditions. Sixteen subjects performed postural motor tasks in three different positions: 'Lying in a sun lounger', 'Sitting on a bike saddle', and 'Upright on feet'. In each position, three different movement instructions were given; 'Stay stock-still', 'Relax', 'Move easily'. Each combination of position and instruction was performed as single task but also in a dual-task condition with a concurrent calculation task. Brain activity in the right prefrontal cortex was monitored using functional near-infrared spectroscopy. The instruction to 'Stay stock-still' produced higher cortical loads in single-task conditions for all positions compared to all other instructions. The calculation task induced additional brain activity in the same prefrontal area as the motor task. Calculation performance tended to be reduced in the 'Lying'-'Stay stock-still' condition. We discuss the relevance of these findings for learning scenarios in school.

Task Integration Facilitates Multitasking

The aim of this study was to investigate multi-task integration in a continuous tracking task. We were particularly interested in how manipulating task structure in a dual-task situation affects learning of a constant segment embedded in a pursuit-tracking task. Importantly, we examined if dual-task effects could be attributed to task integration by varying the structural similarity and difficulty of the primary and secondary tasks. In Experiment 1 participants performed a pursuit tracking task while counting high-pitched tones and ignoring low-pitched tones. The tones were either presented randomly or structurally 250 ms before each tracking turn. Experiment 2 increased the motor load of the secondary tasks by asking participants to tap their feet to the tones. Experiment 3 further increased motor load of the primary task by increasing its speed and having participants tracking with their non-dominant hand. The results show that dual-task interference can be moderated by secondary task conditions that match the structure of the primary task. Therefore our results support proposals of task integration in continuous tracking paradigms. We conclude that multi-tasking is not always detrimental for motor learning but can be facilitated through task-integration.