Moving Forward: On the Limits of Motor-Based Forward Models.

The human ability to anticipate the consequences that result from action is an essential building block for cognitive, emotional, and social functioning. A dominant view is that this faculty is based on motor predictions, in which a forward model uses a copy of the motor command to predict imminent sensory action-consequences. Although this account was originally conceived to explain the processing of action-outcomes that are tightly coupled to bodily movements, it has been increasingly extrapolated to effects beyond the body. Here, we critically evaluate this generalization and argue that, although there is ample evidence for the role of predictions in the processing of environment-related action-outcomes, there is hitherto little reason to assume that these predictions result from motor-based forward models.

Perception of action-outcomes is shaped by life-long and contextual expectations.

The way humans perceive the outcomes of their actions is strongly colored by their expectations. These expectations can develop over different timescales and are not always complementary. The present work examines how long-term (structural) expectations - developed over a lifetime - and short-term (contextual) expectations jointly affect perception. In two studies, including a pre-registered replication, participants initiated the movement of an ambiguously rotating sphere by operating a rotary switch. In the absence of any learning, participants predominantly perceived the sphere to rotate in the same direction as their rotary action. This bias toward structural expectations was abolished (but not reversed) when participants were exposed to incompatible action-effect contingencies (e.g., clockwise actions causing counterclockwise percepts) during a preceding learning phase. Exposure to compatible action-effect contingencies, however, did not add to the existing structural bias. Together, these findings reveal that perception of action-outcomes results from the combined influence of both long-term and immediate expectations.

Exploring the role of motor and non-motor predictive mechanisms in sensory attenuation: Perceptual and neurophysiological findings.

Sounds that result from our own actions are perceptually and neurophysiologically attenuated compared to sounds with an external origin. This sensory attenuation phenomenon is commonly attributed to prediction processes implicated in motor control. However, accumulating evidence suggests that attenuation effects can also result from prediction processes beyond the motor domain. The aim of the present study was two-fold. First, we attempted to replicate the role of identity-specific motor predictions in sensory attenuation. Second, we set out to examine whether attenuation effects can be observed when tones cannot be predicted from preceding actions, but only from the non-motor cues accompanying them. Participants completed a two-alternative forced choice task on the loudness of tones whose pitch was congruent or incongruent with previously learned key-tone or cue-tone associations. No convincing evidence was observed for identity predictions on a perceptual level nor on a neurophysiological level. However, exploratory analyses revealed that attenuation was more pronounced for participants who first learned to rely on motor (instead of non-motor predictions). Together, these findings suggest that the role of motor identity predictions in sensory attenuation might have to be reconsidered.

The influence of action-effect anticipation on bistable perception: differences between onset rivalry and ambiguous motion.

Perception is strongly shaped by the actions we perform. According to the theory of event coding, and forward models of motor control, goal-directed action preparation activates representations of desired effects. These expectations about the precise stimulus identity of one's action-outcomes (i.e. identity predictions) are thought to selectively influence perceptual processing of action-contingent effects. However, the existing evidence for such identity-prediction effects is scarce and mixed. Here, we developed a new paradigm to capture such effects and examined whether action-outcome predictions can bias the perception of binocular onset rivalry (Experiments 1a and 1b) and bistable motion (Experiment 2). Participants performed learning tasks in which they were exposed to action-outcome associations. On test trials, actions were followed by bistable stimuli that could be perceived as being either congruent or incongruent with the aforementioned associations (i.e. rivalrous oriented gratings in Experiments 1a and 1b and spheres with ambiguous rotation directions in Experiment 2). Across three experiments, we show that, whilst exposure to action-effect associations can bias the apparent motion direction of ambiguous spheres, it fails to influence perceptual selection of grating orientations in binocular onset rivalry. This pattern of results extends previous work on ambiguous motion by demonstrating that action-induced modulations do not generalize to all types of bistable percepts.

Cortical information flow during inferences of agency.

Building on the recent finding that agency experiences do not merely rely on sensorimotor information but also on cognitive cues, this exploratory study uses electroencephalographic recordings to examine functional connectivity during agency inference processing in a setting where action and outcome are independent. Participants completed a computerized task in which they pressed a button followed by one of two color words (red or blue) and rated their experienced agency over producing the color. Before executing the action, a matching or mismatching color word was pre-activated by explicitly instructing participants to produce the color (goal condition) or by briefly presenting the color word (prime condition). In both conditions, experienced agency was higher in matching vs. mismatching trials. Furthermore, increased electroencephalography (EEG)-based connectivity strength was observed between parietal and frontal nodes and within the (pre)frontal cortex when color-outcomes matched with goals and participants reported high agency. This pattern of increased connectivity was not identified in trials where outcomes were pre-activated through primes. These results suggest that different connections are involved in the experience and in the loss of agency, as well as in inferences of agency resulting from different types of pre-activation. Moreover, the findings provide novel support for the involvement of a fronto-parietal network in agency inferences.

When moving without volition: implied self-causation enhances binding strength between involuntary actions and effects.

The conscious awareness of voluntary action is associated with systematic changes in time perception: The interval between actions and outcomes is experienced as compressed in time. Although this temporal binding is thought to result from voluntary movement and provides a window to the sense of agency, recent studies challenge this idea by demonstrating binding in involuntary movement. We offer a potential account for these findings by proposing that binding between involuntary actions and effects can occur when self-causation is implied. Participants made temporal judgements concerning a key press and a tone, while they learned to consider themselves as the cause of the effect or not. Results showed that implied self-causation (vs. no implied self-causation) increased temporal binding. Since intrinsic motor cues of movement were absent, these results suggest that sensory evidence about the key press caused binding in retrospect and in line with the participant's sense of being an agent.

Positive priming and intentional binding: eye-blink rate predicts reward information effects on the sense of agency.

Human society is strongly rooted in people's experiences of agency; that is, the pervasive feeling that one engages in voluntary behavior and causes one's own actions and resulting outcomes. Rewards and positive affect play an important role in the control of voluntary action. However, the role of positive reward signals in the sense of agency is poorly understood. This study examined effects of reward-related information on the sense of agency by employing the intentional binding paradigm. This paradigm measures the extent to which actions and their effects subjectively shift together across time, reflecting a crucial component of people's sense of agency. Results showed that intentional binding is stronger when participants are primed with reward-related information via brief exposure to positive pictures. Interestingly, this positive priming effect was moderated by baseline eye-blink rates (an indirect marker of striatal dopaminergic functioning); reward-related information increased intentional binding mainly for participants displaying higher baseline eye-blink rates. These findings suggest a possible role for striatal dopamine activity in the process by which reward-related information shapes the way people see themselves as agents.