Unconscious semantic priming from pictures under backward masking and continuous flash suppression.

It is debated whether the meaning of invisible pictures can be processed unconsciously. We tested whether pictures of animals or objects presented under backward masking or continuous flash suppression could prime the subsequent categorization of target words into animal or non-animal. In Experiment 1, the backward masking part failed to replicate the priming effect reported in two previous studies, despite sufficient statistical power (N = 59). Similarly, the continuous flash suppression part provided no evidence for a priming effect. In Experiment 2 (N = 65) we shortened the prime-target SOA from 290 ms to 90 ms, but again failed to obtain unconscious semantic priming under backward masking. Thus, our study did not provide evidence for unconscious semantic processing of pictures. These findings support the emerging view that unconscious processing is rather limited in scope.

Spontaneous eyeblinks during breaking continuous flash suppression are associated with increased detection times.

An eyeblink has a clear effect on low-level information processing because it temporarily occludes all visual information. Recent evidence suggests that eyeblinks can also modulate higher level processes (e.g., attentional resources), and vice versa. Despite these putative effects on different levels of information processing, eyeblinks are typically neglected in vision and in consciousness research. The main aim of this study was to investigate the timing and the effect of eyeblinks in an increasingly popular paradigm in consciousness research, namely breaking continuous flash suppression (b-CFS). Results show that participants generally refrain from blinking during a trial, that is, when they need to detect a suppressed stimulus. However, when they do blink during a trial, we observed a sharp increase in suppression time. This suggests that one needs to control for blinking when comparing detection times between conditions that could elicit phasic changes in blinking.

Feeling the conflict: the crucial role of conflict experience in adaptation.

In the study reported here, we examined the role of conflict experience in cognitive adaptation to conflict. Although the experience of conflict is generally neglected in theoretical models of cognitive control, we demonstrated that it plays a critical role in cognitive adaptation. Using a masked-priming paradigm, we showed that conflict adaptation was present only after trials on which participants experienced response conflict. Furthermore, when subjective experience did not coincide with actual conflict, adaptation effects in the error rates were observed after the experience of conflict, not after response conflict. We conclude that the experience of conflict, and not response conflict per se, is the crucial factor underlying cognitive adaptation effects. The current findings provide a new perspective on the question of why the human cognitive system exerts cognitive control, and they suggest that a crucial role of subjective experience is to allow for top-down control of behavior.

Distinct brain mechanisms for conscious versus subliminal error detection.

Metacognition, the ability to monitor one's own cognitive processes, is frequently assumed to be univocally associated with conscious processing. However, some monitoring processes, such as those associated with the evaluation of one's own performance, may conceivably be sufficiently automatized to be deployed non-consciously. Here, we used simultaneous electro- and magneto-encephalography (EEG/MEG) to investigate how error detection is modulated by perceptual awareness of a masked target digit. The Error-Related Negativity (ERN), an EEG component occurring ~100 ms after an erroneous response, was exclusively observed on conscious trials: regardless of masking strength, the amplitude of the ERN showed a step-like increase when the stimulus became visible. Nevertheless, even in the absence of an ERN, participants still managed to detect their errors at above-chance levels under subliminal conditions. Error detection on conscious trials originated from the posterior cingulate cortex, while a small response to non-conscious errors was seen in dorsal anterior cingulate. We propose the existence of two distinct brain mechanisms for metacognitive judgements: a conscious all-or-none process of single-trial response evaluation, and a non-conscious statistical assessment of confidence.

Unconscious information integration: A replication and the role of spatial window in masking experiments.

Consciousness and high-level information integration have commonly been closely related to each other (Baars, 2002; Dehaene & Naccache, 2001; Tononi, 2004). Different results, however, have challenged this assumption by showing that information integration can occur for stimuli presented outside of conscious awareness. More recently, a re-examination of some of the data and different replication attempts questioned these results thereby again suggesting a close link between consciousness and information integration. The current study aimed at (i) replicating another piece of evidence for unconscious information integration and (ii) investigating if the size of the spatial window in which the information to be integrated is presented could explain why unconscious information integration sometimes fails. Results showed a reliable replication so providing further evidence for unconscious information integration in a subliminal priming paradigm. Furthermore, our results revealed that unconscious integration depends on the size of the spatial window in which the information is presented.

Dynamic Weighting of Time-Varying Visual and Auditory Evidence During Multisensory Decision Making.

Perceptual decision-making in a dynamic environment requires two integration processes: integration of sensory evidence from multiple modalities to form a coherent representation of the environment, and integration of evidence across time to accurately make a decision. Only recently studies started to unravel how evidence from two modalities is accumulated across time to form a perceptual decision. One important question is whether information from individual senses contributes equally to multisensory decisions. We designed a new psychophysical task that measures how visual and auditory evidence is weighted across time. Participants were asked to discriminate between two visual gratings, and/or two sounds presented to the right and left ear based on respectively contrast and loudness. We varied the evidence, i.e., the contrast of the gratings and amplitude of the sound, over time. Results showed a significant increase in performance accuracy on multisensory trials compared to unisensory trials, indicating that discriminating between two sources is improved when multisensory information is available. Furthermore, we found that early evidence contributed most to sensory decisions. Weighting of unisensory information during audiovisual decision-making dynamically changed over time. A first epoch was characterized by both visual and auditory weighting, during the second epoch vision dominated and the third epoch finalized the weighting profile with auditory dominance. Our results suggest that during our task multisensory improvement is generated by a mechanism that requires cross-modal interactions but also dynamically evokes dominance switching.

Setting the stage subliminally: unconscious context effects.

An important approach to understand how the brain gives rise to consciousness is to probe the depth of unconscious processing, thus to define the key features that cause conscious awareness. Here, we investigate the possibility for subliminal stimuli to shape the context for unconscious processing. Context effects have generally been assumed to require consciousness. In the present experiment, unconscious context processing was investigated by looking at the impact of the context on the response activation elicited by a subliminal prime. We compared the effects of the same subliminal prime on target processing when the prime was embedded in different unconscious contexts. Results showed that the same prime can evoke opposite responses depending on the unconscious context in which it is presented. Taken together, the results of this study show that context effects can be unconscious.

Local build-up of sleep pressure could trigger mind wandering: Evidence from sleep, circadian and mind wandering research.

Mind wandering (MW), or having thoughts unrelated to the task at hand, is a very pervasive phenomenon. Although research on MW has exponentially grown during the last decade and a half, the mechanisms behind this omnipresent phenomenon remain largely unknown. In this review, we will discuss some factors that have been shown to contribute to the occurrence of MW: the quality of sleep, the time of day when the task is performed, the chronotype of the individual and the duration of the task. The intriguing commonality between these specific factors is that they all suggest a relation between MW and sleep pressure. In line with recent work relating MW to local sleep-like activity, we here will argue that one of the mechanisms underlying the pervasiveness of MW might be the local build-up of homeostatic sleep pressure that inevitably occurs during task performance in the brain areas related to the task. Mind wandering could then occur not only to serve a biological purpose, e.g. brain protection, but also a functional one, e.g. off-line learning, that can be beneficial for behavioral performance.

Local use-dependent activity triggers mind wandering: Resource depletion or executive dysfunction?

Mind wandering (MW) is a highly prevalent phenomenon despite its negative consequences on behavior. Current views about its origin share the idea that MW occurs due to changes in the executive functions system. Here, we argue that not all instances of MW are necessarily related to changes in that system. Combining results from MW and sleep research, we propose that MW could also be related to the depletion of resources in primary task-related networks. To test this hypothesis, participants performed four sessions of the texture discrimination task (TDT) on a day. The TDT is a perceptual learning task in which performance is negatively related to the local build-up of sleep pressure. During the TDT, MW was recorded in both a subjective (i.e., with thought probes) and an objective (i.e., phasic pupillary response) manner. Results showed that accuracy on the TDT was mirrored in the objective measure of MW. For the subjective measure, the pattern was similar to that of task performance but could not be interpreted as reliable. These results demonstrate that not all MW is necessarily related to changes in the executive system and support the hypothesis that MW could be related to the depletion of local, task-related resources. (PsycInfo Database Record (c) 2021 APA, all rights reserved).

Hippocampal contribution to early and later stages of implicit motor sequence learning.

Implicit motor sequence learning refers to an important human ability to acquire new motor skills through the repeated performance of a motor sequence. This learning process is characterized by slow, incremental gains of motor performance. The present fMRI study was developed to better delineate the areas supporting these temporal dynamics of learning. By using the serial color matching paradigm, our study focused on the motor level of sequence learning and tracked the time course of learning-related neural changes. Imaging results showed a significant contribution of the left anterior hippocampus in an early sequence acquisition stage (first scanning session) as well as during a later stage with stabilized learning effects (second scanning session). Hippocampal activation significantly correlated with the behavioral learning process and was affected by a change of the motor sequence. These results suggest a strong involvement of the hippocampus in implicit motor sequence learning. On the other hand, a very extensive and bilateral neural network of parietal, temporal and frontal cortical areas (including SMA, pre-SMA) together with parts of the cerebellum and striatum were found to play a role during random visuo-motor task performance.

Unconscious task application.

The nature of unconscious information processing is a heavily debated issue in cognitive science (e.g., Kouider & Dehaene, 2007), and neuroscience (e.g., Crick & Koch, 1998). Traditionally, it has been thought that unconscious cognitive processing is restricted to knowledge that is strongly prepared by conscious processes (e.g., Dehaene et al., 1998). In three experiments, we show that the task that is performed consciously can also be applied unconsciously to items outside the current task set. We found that a same-different judgment of two target stimuli was also performed on two subliminally presented prime stimuli. This was true for target and prime stimuli from entirely different categories, as well as for prime and target stimuli at different levels of abstraction. These results reveal that unconscious processing can generalize more widely than previously accepted.

Influence of content and intensity of thought on behavioral and pupil changes during active mind-wandering, off-focus, and on-task states.

Mind wandering (MW) is a pervasive phenomenon that occurs very frequently, regardless of the task. A content-based definition of MW holds that it occurs when the content of thought switches from an ongoing task and/or an external stimulus-driven event to self-generated or inner thoughts. A recent account suggests that the transition between these different states of attention occurs via an off-focus state. Following this suggestion, previous work relating MW to pupil size might have lumped attentional states that are critically different from each (i.e., off-focus and MW states). In the present study, both behavior and pupil size were measured during a sustained-attention-to-response task, to disentangle the content of thought (on task or MW) from an off-focus state of mind. The off-focus state was operationalized by probing the intensity with which participants were on task or mind-wandering. The results of two experiments showed that the behavioral and phasic pupillary responses were sensitive to changes related to the content of thought. The behavioral responses were furthermore related to the intensity of the thought. However, no clear relation between the different attentional states and tonic pupillary diameter was found, suggesting that it is an unreliable proxy for MW.

The neural representation of extensively trained ordered sequences.

The role of the intraparietal sulcus (IPS) in number processing is largely agreed on. A current debate however concerns the specificity of the involvement of the IPS in representing numbers or ordinal sequences more generally. To test this specificity, we investigated whether the IPS would be activated by extensive training on an arbitrary ordered sequence. We found that the hippocampal-angular gyrus activation initially involved in learning the ordered sequences extends with extensive training to the left inferior frontal gyrus (left IFG), but not to the IPS. These results suggest that left IFG can be involved in processing ordinal information, and that there is no need for an IPS area specifically dedicated to the representation of all ordinal sequences. Instead, we propose that the locus of the representation might be determined by the nature of the stimuli rather than its ordinal nature per se.

Striatal dopamine D2 binding correlates with locus of control: Preliminary evidence from [11C]raclopride Positron Emission Tomography.

The ability to exert control has been widely investigated as a hallmark of adaptive behaviour. Dopamine is recognized as the key neuromodulator mediating various control-related processes. The neural mechanisms underlying the subjective perception of being in control, or Locus of Control (LOC) are however less clear. LOC indicates the subjective tendency to attribute environmental outcomes to one's actions (internal LOC) or instead to external incontrollable factors (external LOC). Here we hypothesized that dopamine levels also relate to LOC. Previous work shows that dopamine signaling mediates learning of action-outcome relationships, outcome predictability, and opportunity cost. Prominent theories propose dopamine dysregulation as the key pathogenetic mechanism in schizophrenia and depression. Critically, external LOC is a risk factor for schizophrenia and depression, and predicts increased vulnerability to stress. However, a direct link between LOC and dopamine levels in healthy control had not been demonstrated. The purpose of our study was to investigate this link. Using [11C]raclopride Positron Emission Tomography we tested the relationship between D2 receptor binding in the striatum and LOC (measured with the Rotter Locus of Control scale) in 15 healthy volunteers. Our results show a large and positive correlation: increased striatal D2 binding was associated with External LOC. This finding opens promising avenues for the study of several psychological impairments that have been associated with both dopamine and LOC, such as addiction, schizophrenia, and depression.

A colorful walk, but is it on the mental number line? Reply to Cohen Kadosh, Tzelgov, and Henik.

Cohen Kadosh, Tzelgov, and Henik [Cohen Kadosh, R., Tzelgov, J., and Henik, A. (2008). A synesthetic walk on the number line: The size effect. Cognition, 106, 548-557] present a new paradigm to probe properties of the mental number line. They describe two experiments which they argue to be inconsistent with the exact small number model proposed by Verguts, Fias, and Stevens [Verguts, T., Fias, W., Stevens, M. (2005). A model of exact small-number representation. Psychonomic Bulletin and Review, 12, 66-80]. We discuss the data, assumptions, and conclusions of Cohen Kadosh et al.'s paper in relation to existing models of numerical cognition.

Dissecting the symbolic distance effect: comparison and priming effects in numerical and nonnumerical orders.

When participants are asked to compare two stimuli, responses are slower for stimuli close to each other on the relevant dimension than for stimuli further apart. Previously, it has been proposed that this comparison distance effect originates from overlap in the representation of the stimuli. This idea is generally accepted in numerical cognition, where it is assumed that representational overlap of numbers on a mental number line accounts for the effect (e.g., Cohen Kadosh et al., 2005). In contrast, others have emphasized the role of response-related processes to explain the comparison distance effect (e.g., Banks, 1977). In the present study, numbers and letters are used to show that the comparison distance effect can be dissociated from a more direct behavioral signature of representational overlap, the priming distance effect. The implication is that a comparison distance effect does not imply representational overlap. An interpretation is given in terms of a recently proposed model of quantity comparison (Verguts, Fias, & Stevens, 2005).

Task-Relevant Information Modulates Primary Motor Cortex Activity Before Movement Onset.

Monkey neurophysiology research supports the affordance competition hypothesis (ACH) proposing that cognitive information useful for action selection is integrated in sensorimotor areas. In this view, action selection would emerge from the simultaneous representation of competing action plans, in parallel biased by relevant task factors. This biased competition would take place up to primary motor cortex (M1). Although ACH is plausible in environments affording choices between actions, its relevance for human decision making is less clear. To address this issue, we designed an functional magnetic resonance imaging (fMRI) experiment modeled after monkey neurophysiology studies in which human participants processed cues conveying predictive information about upcoming button presses. Our results demonstrate that, as predicted by the ACH, predictive information (i.e., the relevant task factor) biases activity of primary motor regions. Specifically, first, activity before movement onset in contralateral M1 increases as the competition is biased in favor of a specific button press relative to activity in ipsilateral M1. Second, motor regions were more tightly coupled with fronto-parietal regions when competition between potential actions was high, again suggesting that motor regions are also part of the biased competition network. Our findings support the idea that action planning dynamics as proposed in the ACH are valid both in human and non-human primates.

Metacognition and cognitive control: behavioural adaptation requires conflict experience.

Cognitive control allows adapting our behaviour to improve performance. A behavioural signature of cognitive control is the Gratton effect. This effect is observed in conflict tasks and indicates smaller congruency effects after incongruent trials than after congruent trials. Metacognitive experience may play a role in this effect: When participants introspect on their conflict experience, the Gratton effect follows the conflict introspection instead of the stimulus congruency. However this Gratton effect could also be triggered by the labelling that the introspective method implies and/or by a misperception of the stimulus conflict. The current study investigated whether the experiential component of the introspection is necessary to trigger cognitive control or whether labelling a trial as conflicting or not can be sufficient. In a priming task, Gratton effects following metacognitive conflict experience and conflict label were contrasted. Replicating earlier reports, results showed that the metacognitive experience of conflict can trigger a Gratton effect. However a conflict label, either generated by the participants themselves or presented to the participants via feedback was not able to induce cognitive control. Results are discussed in light of current theories of cognitive control.

Signed reward prediction errors drive declarative learning.

Reward prediction errors (RPEs) are thought to drive learning. This has been established in procedural learning (e.g., classical and operant conditioning). However, empirical evidence on whether RPEs drive declarative learning-a quintessentially human form of learning-remains surprisingly absent. We therefore coupled RPEs to the acquisition of Dutch-Swahili word pairs in a declarative learning paradigm. Signed RPEs (SRPEs; "better-than-expected" signals) during declarative learning improved recognition in a follow-up test, with increasingly positive RPEs leading to better recognition. In addition, classic declarative memory mechanisms such as time-on-task failed to explain recognition performance. The beneficial effect of SRPEs on recognition was subsequently affirmed in a replication study with visual stimuli.

Subjective experience of difficulty depends on multiple cues.

Human cognition is characterized by subjective experiences that go along with our actions, but the nature and stability of these experiences remain largely unclear. In the current report, the subjective experience of difficulty is studied and it is proposed that this experience is constructed by integrating information from multiple cues. Such an account can explain the tight relationship between primary task performance and subjective difficulty, while allowing for dissociations between both to occur. Confirming this hypothesis, response conflict, reaction time and response repetition were identified as variables that contribute to the experience of difficulty. Trials that were congruent, fast or required the same response as the previous trial were more frequently rated as easy than trials that were incongruent, slow or required a different response as the previous trial. Furthermore, in line with theoretical accounts that relate metacognition to learning, a three day training procedure showed that the influence of these variables on subjective difficulty judgments can be changed. Results of the current study are discussed in relation to work on meta-memory and to recent theoretical advancements in the understanding of subjective confidence.