Attention and expectation likely underlie temporal binding measured using the Libet Clock.

An interesting finding that has emerged in studies of the sense of agency is that of a perceived compression of the temporal interval between actions and the outcomes they produce. This is generally referred to as temporal binding. Although temporal binding has been studied using various paradigms, possibly the most popular of these is the Libet Clock task. The Libet task is also interesting because it suggests that temporal binding can be decomposed into two components, one purportedly relating to actions and the other relating to outcomes. These are termed action binding and outcome binding, respectively. In this article, I focus specifically on temporal binding revealed using the Libet Clock task and propose the idea that attention underpins the action binding effect, while outcome binding, on the other hand, is driven by the effects of expectation.

Having a sense of agency can improve memory.

In most situations, we are able to tell those outcomes we cause from those we do not. By now, research has provided us with a reasonably good understanding of the cognitive processes that underlie this sense of agency - it is thought to be produced by a comparison between a prediction of the outcome and the actual outcome that occurs. What is less clear is whether having a sense of agency can, itself, influence cognition. In the current study, we examined the possibility that sense of agency can affect memory, and we report evidence that stimuli that one feels a sense of agency over are, in fact, better remembered than counterparts without this. This self-agency effect can be distinguished from previously described control-related memory enhancements and adds to what we know of the cognitive consequences of having a sense of agency.

Outcome processing and the sense of agency.

People can distinguish outcomes they cause from those they do not; that is, they are quite able to sense self-agency in outcomes. A well-received idea is that the sense of agency is produced by a comparison between a predicted outcome and the actual outcome that occurs. While research has generally focused on understanding predictive representations and the comparison process, less work has been done on the actual outcomes and, in particular, how these are perceived or apprehended. Here, we studied this issue. In two experiments, we found outcomes are continuously, as opposed to partially, sampled throughout their span. Specifically, we found that prediction-inconsistent signals embedded within otherwise prediction-consistent outcomes were able to influence agency ratings, and this was true whether the contrary signals were embedded early or late in the outcome.

Learning in the Target Prevalence Effect.

Rare or low prevalence targets are detected less well than counterparts that occur with higher probability. It stands to reason, though, that before such a deficit is apparent, information about a given target's probability of occurrence must be apprehended. In this study, we investigated how much target experience is necessary for target probabilities to be fully acquired and established within mental task representations. A central finding was that different target probability values required approximately the same amount of target sampling to learn. This was true whether learning about target probabilities from a naive start-point (Experiment 1) or when recalibrating from one probability value to another (Experiment 2). We discuss these findings in relation to how mental task representations are modified when new task-relevant information is received and the attentional consequences of such changes.

Outside influence: The sense of agency takes into account what is in our surroundings.

We are quite capable of distinguishing those outcomes we cause from those we do not. This ability to sense self-agency is thought to be produced by a comparison between a predictive representation of an outcome and the actual outcome that occurs. It is unclear, though, specifically what types of information can be entered into agency computations. Here, we demonstrate that information from non-target stimuli (stimuli that are not directly acted upon) incidentally present in our surroundings can influence predictions of outcomes, consequently modulating the sense of agency over clearly-defined target outcomes (those that occur to acted-upon stimuli). This provides the first evidence that our sense of agency is contextualized with respect to what is in our immediate visual environment. Furthermore, our data suggest that agency computations, instead of just a single comparison, may involve comparisons performed in stages, with different stages involving different types/classes of information. A model of such multi-stage comparisons is described.

Attention and the sense of agency: A review and some thoughts on the matter.

Much is now known about the sense of agency and how it is produced. What is lacking, though, is an understanding of how it relates to other cognitive domains and operations. Here, the relationship between the sense of agency and attention is explored. A review of the literature suggests that attention is involved in the sense of agency in (at least) two key ways. First, agency processing is dependent on attentional resources. Second, attentional enhancement is necessary for extraneous information to have an influence over the sense of agency. These are discussed and some suggestions for future research are offered.

Striatal activity is modulated by target probability.

Target probability has well-known neural effects. In the brain, target probability is known to affect frontal activity, with lower probability targets producing more prefrontal activation than those that occur with higher probability. Although the effect of target probability on cortical activity is well specified, its effect on subcortical structures such as the striatum is less well understood. Here, I examined this issue and found that the striatum was highly responsive to target probability. This is consistent with its hypothesized role in the gating of salient information into higher-order task representations. The current data are interpreted in light of that fact that different components of the striatum are sensitive to different types of task-relevant information.

A response time cost when different representations of an attended object are integrated.

When selected, attention is thought to spread across the whole of an object. Such spreading is thought to occur via the integration and mutual enhancement of the different mental representations of said object. Neurophysiological studies have demonstrated that such integration is not instantaneous with selection, but rather occurs after some delay. It is currently unclear whether the time needed for integration to be established has a behavioural consequence. Here, it was found that trials that required integration were responded to more slowly than those that did not, even though correct responses in both could be determined by the same information. These data thus suggest that the time taken for integration between representations to be established has a consequence on behaviour, one that can be observed as a response time cost. Furthermore, these findings enlighten the time-course of integration vis-a-vis the processing of information at different levels of the processing stream.

Sleep deprivation produces feelings of vicarious agency.

A variety of self-related psychological constructs are supported by the fundamental ability to accurately sense either self-agency or lack of agency in some action or outcome. Agency judgments are typically studied in individuals who are well-rested and mentally-fresh; however, in our increasingly fast-paced world, such judgments often need to be made while in less optimal states. Here, we studied the effect of being in one such non-optimal state - when sleep-deprived - on judgments of agency. We found that 24h of total sleep deprivation elevated agency ratings on trials designed to produce a strong sense of non-agency. These data provide the first evidence that physiological state variables can affect agency processing in the normal population.

Rare targets are less susceptible to attention capture once detection has begun.

Rare or low probability targets are detected more slowly and/ or less accurately than higher probability counterparts. Various proposals have implicated perceptual and response-based processes in this deficit. Recent evidence, however, suggests that it is attentional in nature, with low probability targets requiring more attentional resources than high probability ones to detect. This difference in attentional requirements, in turn, suggests the possibility that low and high probability targets may have different susceptibilities to attention capture, which is also known to be resource-dependent. Supporting this hypothesis, we found that, once attentional resources have begun to be engaged by detection processes, low, but not high, probability targets have a reduced susceptibility to capture. Our findings speak to several issues. First, they indicate that the likelihood of attention capture occurring when a given task-relevant stimulus is being processed is dependent, to some extent, on how said stimulus is represented within mental task sets. Second, they provide added support for the idea that the behavioural deficit associated with low probability targets is attention-based. Finally, the current data point to reduced top-down biasing of target templates as a likely mechanism underlying the attentional locus of the deficit in question.

Preoccupied minds feel less control: sense of agency is modulated by cognitive load.

People have little difficulty distinguishing effects they cause and those they do not. An important question is what underlies this sense of agency. A prevailing idea is that the sense of agency arises from a comparison between a predictive representation of the effect (of a given action) and the actual effect that occurs, with a clear match between the two producing a strong sense of agency. Although there is general agreement on this comparison process, one important theoretical issue that has yet to be fully determined is whether these computations are consciously performed. Here, we studied this issue by requiring participants to perform a simple judgment of agency task under conditions of different concurrent working memory load. Working memory operations are known to tax conscious cognitive resources. We found that agency judgments were moderated by working memory load, with lower agency ratings being observed in the high load condition, suggesting that the sense of agency is dependent on the availability of conscious cognitive resources. An examination of the time-course of this load effect suggests that it is the construction of the mental representation of the predicted effect which is particularly dependent on said resources.

Why rare targets are slow: evidence that the target probability effect has an attentional locus.

Target probability has a well-known effect on detection times: Targets that occur with lower probability are detected more slowly than their higher-probability counterparts. A long-standing issue of interest is what causes this effect. In the two experiments of this study, we examined the possibility that the target probability effect has an attentional locus. We report two key findings that are consistent with this hypothesis. First, we observed a magnification of the effect when the attentional resources available for target detection were limited. Second, we also observed the complementary pattern: an attenuation of the effect when more attentional resources were available for detection. We propose that the target probability effect is caused by an asymmetry in the attentional demands made by targets that occur with different probabilities, with low-probability targets being more attentionally demanding than high-probability ones.

The trajectory of the target probability effect.

The effect of target probability on detection times is well-established: Even when detection accuracy is high, lower probability targets are detected more slowly than higher probability ones. Although this target probability effect on detection times has been well-studied, one aspect of it has remained largely unexamined: How the effect develops over the span of an experiment. Here, we investigated this issue with two detection experiments that assessed different target probability ratios. Conventional block segment analysis and linear mixed-effects modeling converged on two key findings. First, we found that the magnitude of the target probability effect increases as one progresses through a block of trials. Second, we found, by examining the trajectories of the low- and high-probability targets, that this increase in effect magnitude was driven by the low-probability targets. Specifically, we found that low-probability targets were detected more slowly as a block of trials progressed. Performance to high-probability targets, on the other hand, was largely invariant across the block. The latter finding is of particular interest because it cannot be reconciled with accounts that propose that the target probability effect is driven by the high-probability targets.

Dysconnectivity in the frontoparietal attention network in schizophrenia.

Cognitive impairment is common in patients with schizophrenia, and even those with relatively preserved function perform worse than healthy volunteers (HVs) on attentional tasks. This is consistent with the hypothesis that connectivity - in the frontoparietal network (FPN) activated during attention - is disrupted in schizophrenia. We examined attentional effects on connectivity in the FPN, in schizophrenia, using magnetoencephalography (MEG). Twenty-three HVs and 19 first-episode schizophrenia patients were scanned during a simple visual change test, known to activate the FPN, in which attention was monitored and directed with an orthogonal flicker-detection task. Dynamic causal modeling (DCM) of evoked responses was used to assess effective connectivity - and its modulation by changes in the attended stimulus dimension - in the following network: higher visual area; temporoparietal junction (TPJ); intraparietal sulcus (IPS); dorsal anterior cingulate cortex; and ventrolateral prefrontal cortex. The final MEG analysis included 18 HVs and 14 schizophrenia patients. While all participants were able to maintain attention, HVs responded slightly, but non-significantly, more accurately than schizophrenia patients. HVs, but not schizophrenia patients, exhibited greater cortical responses to attended visual changes. Bayesian model comparison revealed that a DCM with attention dependent changes in both top-down and bottom-up connections best explained responses by patients with schizophrenia, while in HVs the best model required only bottom-up changes. Quantitative comparison of connectivity estimates revealed a significant group difference in changes in the right IPS-TPJ connection: schizophrenia patients showed relative reductions in connectivity during attended stimulus changes. Crucially, this reduction predicted lower intelligence. These data are consistent with the hypothesis that functional dysconnections in the FPN contribute to cognitive impairment in schizophrenia.

Different types of target probability have different prefrontal consequences.

One of the factors known to affect target detection is target probability. It is clear, though, that target probability can be manipulated in different ways. Here, in order to more accurately characterize the effects of target probability on frontal engagement, we examined the effects of two commonly-used but different target probability manipulations on neural activity. We found that manipulations that affected global stimulus class probability had a pronounced effect on ventrolateral prefrontal cortex and the insula, an effect which was absent with manipulations that only affected the likelihood of specific target stimuli occurring. This latter manipulation only modulated activity in dorsolateral prefrontal cortex and the precentral sulcus. Our data suggest two key points. First, different types of target probability have different neural consequences, and may therefore be very different in nature. Second, the data indicate that ventral and dorsal portions of prefrontal cortex respond to different types of task-relevant information.

Evidence for long-range feedback in target detection: Detection of semantic targets modulates activity in early visual areas.

In a variety of attention and search tasks, single-cell recordings of the primate brain have frequently shown an enhancement of responses in early visual areas to selected target stimuli. This enhancement is observed only at longer latencies, suggesting the possibility that it reflects the action of feedback or return signals from upstream processing areas. However, in typical studies, targets are specified on the basis of elementary visual features; as these are coded at multiple levels of the visual system, it is impossible to determine where enhanced target processing begins. Using human functional magnetic resonance imaging (fMRI), we demonstrate enhancement of activity in early visual areas even when low-level visual information is insufficient for target detection to occur. We found enhanced activity in early visual areas to targets defined purely by semantic category, suggesting that feedback signals returning from at least as far forward as temporal lobe semantic processing can influence visual responses. These findings also suggest feedback signaling as a mechanism by which early and late brain systems coding for different properties of a target object can integrate their activity, allowing for the target object to dominate overall processing.

A discussion of the role of frontoparietal activity in cognition.

A consistently observed pattern in the functional brain imaging literature is that of joint frontal and parietal activation. Because this pattern of activation has been observed under many different experimental conditions and when different cognitive domains have been tested, it is likely that frontoparietal activity plays a very general role in cognition. This article considers one such possible role--the representation of behaviorally relevant information.

Frontoparietal activity with minimal decision and control.

In the human brain, a well known frontoparietal circuit, including lateral prefrontal cortex (LPFC), presupplementary motor area/anterior cingulate cortex (pre-SMA/ACC), and both the superior and inferior parietal cortex, is involved in cognitive control. One proposal is that the frontoparietal cortex holds a flexible description of attended or task-relevant information, biasing processing in favor of this information in many different parts of the brain. Here, we separate frontoparietal coding of attended information from its active use in behavior. In two experiments, subjects watch a stream of visual stimuli in a fixed location. In the first experiment, there is no task to perform; in the second, decisions are orthogonal to the occurrence of new stimulus events. Even in these simple circumstances, we find that attended stimulus changes give extensive activation of LPFC, pre-SMA/ACC and parietal cortex, whereas unattended changes do not. Even without behavior to control, these classical "control" regions are active in simple update of attended information.

Frequency of concrete words modulates prefrontal activation during semantic judgments.

The effect of word frequency on semantic processing was characterized by studying two groups of right-handed participants using fMRI. Stimuli were presented in blocks of either high frequency or low frequency word triplets where a sample word appeared above a pair of test words. One group (n = 8) made semantic judgments by selecting the word from the test pair that was more closely associated with the sample. Stimulus triplets were designed such that relatedness between sample and "correct" items was obvious. The other group (n = 8) read the words silently without making any semantic decision and pressed a button on completing the reading of each triplet. Semantic judgments while no less accurate, were associated with greater left prefrontal BOLD signal change when they involved low frequency words, whereas there was no reliable effect of word frequency in the reading condition. These findings suggest that retrieval effort modulates left prefrontal activity when deliberate access to semantics is required.