Dorit Wenke

Disrupting the experience of control in the human brain: pre-supplementary motor area contributes to the sense of agency

The feeling of controlling events through ones actions is fundamental to human experience, but its neural basis remains unclear. This ‘sense of agency’ (SoA) can be measured quantitatively as a temporal linkage between voluntary actions and their external effects. We investigated the brain areas underlying this aspect of action awareness by using theta-burst stimulation to locally and reversibly disrupt human brain function. Disruption of the pre-supplementary motor area (pre-SMA), a key structure for preparation and initiation of a voluntary action, was shown to reduce the temporal linkage between a voluntary key-press action and a subsequent electrocutaneous stimulus. In contrast, disruption of the sensorimotor cortex, which processes signals more directly related to action execution and sensory feedback, had no significant effect. Our results provide the first direct evidence of a pre-SMA contribution to SoA.

Subliminal priming of actions influences sense of control over effects of action

The experience of controlling ones own actions, and through them events in the outside world, is a pervasive feature of human mental life. Two experiments investigated the relation between this sense of control and the internal processes involved in action selection and cognitive control. Action selection was manipulated by subliminally priming left or right keypress actions in response to a supraliminal visual target. The action caused the display of one of several colours as an action effect. The specific colour shown depended on whether the participants action was compatible or incompatible with the preceding subliminal prime, and not on the prime identity alone. Unlike previous studies, therefore, the primes did not predict the to-be-expected action effects. Participants rated how much control they experienced over the different colours. Replicating previous results, compatible primes facilitated responding, whereas incompatible primes interfered with response selection. Crucially, priming also modulated the sense of control over action effects: participants experienced more control over colours produced by actions that were compatible with the preceding prime than over colours associated with prime-incompatible actions. Experiment 2 showed that this effect was not solely due to priming modulating action-effect contingencies. These results suggest that sense of control is linked to processes of selection between alternative actions, being strongest when selection is smooth and uncontested.

How voluntary actions modulate time perception

Distortions of time perception are generally explained either by variations in the rate of pacing signals of an “internal clock”, or by lag-adaptation mechanisms that recalibrate the perceived time of one event relative to another. This study compares these accounts directly for one temporal illusion: the subjective compression of the interval between voluntary actions and their effects, known as ‘intentional binding’. Participants discriminated whether two cutaneous stimuli presented after voluntary or passive movements were simultaneous or successive. In other trials, they judged the temporal interval between their movement and an ensuing tone. Temporal discrimination was impaired following voluntary movements compared to passive movements early in the action-tone interval. In a control experiment, active movements without subsequent tones produced no impairment in temporal discrimination. These results suggest that voluntary actions transiently slow down an internal clock during the action-effect interval. This in turn leads to intentional binding, and links the effects of voluntary actions to the self.

Trial-to-trial sequential dependencies in a social and non-social Simon task

Recent research has shown that joint-action effects in a social Simon task provide a good index of action co-representation. The present study aimed to specify the mechanisms underlying joint action by considering trial-to-trial transitions. Using non-social stimuli, we assigned a Simon task to two participants. Each was responsible for only one of two possible responses. This task was performed alone (Individual go/nogo task) and in cooperation with another person who was sitting alongside (Joint go/nogo task). As a further control task, we added a Standard Simon task. Replicating previous findings (Sebanz et al. in Cognition 88:B11–B21, 2003), we found no spatial compatibility effect in the Individual go/nogo task but we did find one in the Joint go/nogo task. A more detailed analysis showed that a sequential modulation of the Simon effect was present in both the Joint and the Individual go/nogo tasks. We found reliable Simon effects in trials following Simon compatible trials not only in the Joint go/nogo task but also to a somewhat smaller extent in the Individual go/nogo task. For both these go/nogo tasks, sequential modulation effects were stronger for nogo/go transitions than for go/go transitions. This suggests that low-level feature binding and repetition mechanisms contribute to the social Simon effect related to the specific requirement not to respond on nogo trials.

Instruction-based task-rule congruency effects

In the present study, we investigated the functional characteristics of task sets that were never applied before and were formed only on the basis of instructions. We tested if such task sets could elicit a task-rule congruency effect, which implies the automatic activation of responses in the context of another task. To this end, a novel procedure was developed that revealed instruction-based task-rule congruency effects in 2 experiments. Although the effect seems quite general (Experiment 1), it still necessitates the formation of a task set, as it cannot be induced by the mere maintenance of instructions in declarative working memory (Experiment 2). We conclude that a task set representing only key features of an upcoming task can be formed on the basis of instructions alone to such a degree that it can automatically trigger a response tendency in another task. Implications of our results for the impact of instructions on performance in general and for the occurrence of task-rule congruency effects in particular are discussed.

Neural Correlates of Overcoming Interference from Instructed and Implemented Stimulus–Response Associations

One of the major evolutionary advances of human primates in the motor domain is their ability to use verbal instructions to guide their behavior. Despite this fundamental role of verbal information for our behavioral regulation, the functional and neural mechanisms underlying the transformation of verbal instructions into efficient behavior are still poorly understood. To gain deeper insights into the motor representation of verbal instructions, we investigated the neural circuits involved in overcoming interference from stimulus– response (S-R) mappings that are merely instructed and S-R mappings that are implemented. Implemented and instructed S-R mappings revealed a partly overlapping pattern of fronto-parietal brain activity when compared with a neutral condition. However, the direct contrast revealed a clear difference with stronger activation for the implemented condition in the ACC, bilateral inferior parietal cortex, the cerebellum and the precentral sulcus. This indicates that instructed S-R mappings share some properties with implemented S-R mappings but that they are lacking the motor-related properties of implemented mappings.

Effects of feature integration in a hands-crossed version of the Social Simon paradigm

In previous research, hands-crossed versions of a social variant of the Simon task were used to distinguish between effector-based coding of the Social Simon effect (SSE, analogously to the standard Simon effect) or body-based coding, in which the coding of stimulus location and seating position of the participants functions as a spatial reference frame. In the present study, the analysis of the SSE with respect to previous task requirements (i.e., Simon compatibility in N−1) in a hands-crossed variant of the Social Simon task shows that neither type of coding provides a sole explanation of the pattern of a SSE. Instead, the data pattern seems to be explained more parsimoniously by the assumption of a strengthening of low level feature integration mechanisms in a social setting, taking repetitions and alternations of both agents’ stimulus and response features into account.

Medial prefrontal cortex predicts internally driven strategy shifts.

Many daily behaviors require us to actively focus on the current task and ignore all other distractions. Yet, ignoring everything else might hinder the ability to discover new ways to achieve the same goal. Here, we studied the neural mechanisms that support the spontaneous change to better strategies while an established strategy is executed. Multivariate neuroimaging analyses showed that before the spontaneous change to an alternative strategy, medial prefrontal cortex (MPFC) encoded information that was irrelevant for the current strategy but necessary for the later strategy. Importantly, this neural effect was related to future behavioral changes: information encoding in MPFC was changed only in participants who eventually switched their strategy and started before the actual strategy change. This allowed us to predict spontaneous strategy shifts ahead of time. These findings suggest that MPFC might internally simulate alternative strategies and shed new light on the organization of PFC.

Instruction-based response activation depends on task preparation

An increasing number of studies have demonstrated that a response in one task can be activated automatically on the basis merely of instructed stimulus–response (S–R) mappings belonging to another task. Such instruction-based response activations are considered to be evidence for the formation of S–R associations on the basis of the S–R mappings for an upcoming, but not yet executed, task. A crucial but somewhat neglected assumption is that instructed S–R associations are formed only under conditions that impose a sufficient degree of task preparation. Accordingly, in the present study we investigated the relation between task preparation and the instruction-based task-rule congruency effect, which is an index of response activation on the basis of instructions. The results from two experiments demonstrated that merely instructed S–R mappings of a particular task only elicit instruction-based response activations when that task is prepared for to a sufficient degree. Implications are discussed for the representation of instructed S–R mappings in working memory.

The shielding function of task sets and its relaxation during task switching

The goal of the presented experiments was to investigate the dynamic interplay of task shielding and its relaxation during task switching. Task shielding refers to the finding that single task sets in terms of 2-choice categorization rules help shielding against distraction from irrelevant stimulus attributes. During task switching, this shielding should temporarily be relaxed to prevent the perseveration of the previous task, on the downside making the system more vulnerable toward the intrusion of irrelevant information. Participants had to switch between a digit and a letter categorization task. An irrelevant stimulus feature (Experiment 1: color, Experiment 2: font) varied randomly, orthogonal to the task. The presence or absence of an interaction of the irrelevant feature (switch vs. repetition) and the response (switch vs. repetition) was taken as evidence for the absence or presence of task shielding, respectively. Replicating previous results, irrelevant feature and response did not interact on task repetitions, indicating successful shielding. On task switches, however, the irrelevant feature interacted with the response, supporting the assumption that task shielding is temporarily relaxed during task switching.