EEG mismatch responses in a multimodal roving stimulus paradigm provide evidence for probabilistic inference across audition, somatosensation, and vision.

The human brain is constantly subjected to a multimodal stream of probabilistic sensory inputs. Electroencephalography (EEG) signatures, such as the mismatch negativity (MMN) and the P3, can give valuable insight into neuronal probabilistic inference. Although reported for different modalities, mismatch responses have largely been studied in isolation, with a strong focus on the auditory MMN. To investigate the extent to which early and late mismatch responses across modalities represent comparable signatures of uni- and cross-modal probabilistic inference in the hierarchically structured cortex, we recorded EEG from 32 participants undergoing a novel tri-modal roving stimulus paradigm. The employed sequences consisted of high and low intensity stimuli in the auditory, somatosensory and visual modalities and were governed by unimodal transition probabilities and cross-modal conditional dependencies. We found modality specific signatures of MMN (~100-200 ms) in all three modalities, which were source localized to the respective sensory cortices and shared right lateralized prefrontal sources. Additionally, we identified a cross-modal signature of mismatch processing in the P3a time range (~300-350 ms), for which a common network with frontal dominance was found. Across modalities, the mismatch responses showed highly comparable parametric effects of stimulus train length, which were driven by standard and deviant response modulations in opposite directions. Strikingly, P3a responses across modalities were increased for mispredicted stimuli with low cross-modal conditional probability, suggesting sensitivity to multimodal (global) predictive sequence properties. Finally, model comparisons indicated that the observed single trial dynamics were best captured by Bayesian learning models tracking unimodal stimulus transitions as well as cross-modal conditional dependencies.

Visual attention during cognitive reappraisal in adolescent major depression: Evidence from two eye-tracking studies.

Adolescent major depression (MD) is associated with impaired emotion regulation. However, results on cognitive reappraisal (CR) are mixed. Investigation of gaze behavior during CR allows a more thorough understanding of intact and deviant CR processes in MD. These studies examined for the first time the role of visual attention during CR in MD. We applied an established CR paradigm in two separate studies, with each study focusing on a different CR strategy. In Study 1, we investigated "distancing" in 39 adolescents with MD and 44 healthy controls (HCs). In Study 2, we applied "reinterpretation" in an independent sample of 37 HCs and 19 adolescents with MD. In both studies, adolescents either down-regulated negative affect to negative pictures via CR or attended them, while eye-movements were continuously recorded. Results of both studies showed that adolescents with MD and HCs did not differ in self-reported ER success. The groups showed comparable gaze behaviour patterns for emotional interest areas and entire pictures. Findings suggest that adolescents with MD are capable of applying CR when instructed and show intact visual attention processes. Future studies should examine whether repeatedly instructing adolescents with MD to apply CR might lead to improved emotion regulation in daily life.

Dissociating Perceptual Awareness and Postperceptual Processing: The P300 Is Not a Reliable Marker of Somatosensory Target Detection.

A central challenge in the study of conscious perception lies in dissociating the neural correlates of perceptual awareness from those reflecting its precursors and consequences. No-report paradigms have been instrumental in this endeavor, demonstrating that the event-related potential P300, recorded from the human scalp, reflects reports rather than awareness. However, these paradigms cannot probe the degree to which stimuli are consciously processed from trial to trial and, thus, leave open the possibility that the P300 is a genuine correlate of conscious access enabling reports. Here, instead of removing report requirements, we took the opposite approach and equated postperceptual task demands across conscious and unconscious trials by orthogonalizing target detection and overt reports in a somatosensory detection task. We used Bayesian model selection to track the transformation from physical to perceptual processing stages in the EEG data of 24 male and female participants and show that the early P50 component scaled with physical stimulus intensity, whereas the N140 component was the first correlate of target detection. The late P300 component was elicited for both perceived and unperceived stimuli and was not substantially modulated by target detection. This was in stark contrast to a control experiment using a classical direct report task, which replicated the P50 and N140 effects but additionally showed a strong effect of target detection in the P300 time range. Our results demonstrate the task dependence of the P300 in the somatosensory modality and show that late cortical potentials dissociate from perceptual awareness even when stimuli are always reported.SIGNIFICANCE STATEMENT The time it takes for sensory information to enter our conscious experience can be an indicator of the neural processing stages that lead to perceptual awareness. However, because many cognitive processes routinely correlate with perception, isolating those signals that uniquely reflect perceptual awareness is not a trivial task. Here, we show that late electroencephalography signals cease to correlate with somatosensory awareness when common task confounds are controlled. Importantly, by balancing report requirements instead of abolishing them, we show that the lack of late effects cannot be explained by a lack of conscious access. Instead, we propose that conscious access occurs earlier, at ∼150 ms, supporting the view that early activity in sensory cortices is a neural correlate of conscious perception.

Rehearsal of tactile working memory: Premotor cortex recruits two dissociable neuronal content representations.

Recent working memory (WM) research has focused on identifying brain regions that retain different types of mental content. Only few neuroimaging studies have explored the mechanism of attention-based refreshing, which is a type of rehearsal and is thought to implement the dynamic components of WM allowing for update of WM contents. Here, we took advantage of the distinct coding properties of the superior parietal lobe (SPL), which retains spatial layout information, and the right inferior frontal gyrus (IFG), which retains frequency information of vibrotactile stimuli during tactile WM. In an fMRI delayed match-to-sample task, participants had to internally rehearse sequences of spatial layouts or vibratory frequencies. Our results replicate the dissociation of SPL and IFG for the retention of layout and frequency information in terms of activation differences between conditions. Additionally, we found strong premotor cortex (PMC) activation during rehearsal of either stimulus type. To explore interactions between these regions we used dynamic causal modeling and found that activation within the network was best explained by a model that allows the PMC to drive activity in the SPL and IFG during rehearsal. This effect was content-specific, meaning that the PMC showed stronger influence on the SPL during pattern rehearsal and stronger influence on the IFG during frequency rehearsal. In line with previously established PMC contributions to sequence processing, our results suggest that it acts as a content-independent area that flexibly recruits content-specific regions to bring a WM item into the focus of attention during the rehearsal of tactile stimulus sequences.

Neural basis of somatosensory target detection independent of uncertainty, relevance, and reports.

Research on somatosensory awareness has yielded highly diverse findings with putative neural correlates ranging from activity within somatosensory cortex to activation of widely distributed frontoparietal networks. Divergent results from previous studies may reside in cognitive processes that often coincide with stimulus awareness in experimental settings. To scrutinise the specific relevance of regions implied in the target detection network, we used functional magnetic resonance imaging (n = 27) on a novel somatosensory detection task that explicitly controls for stimulus uncertainty, behavioural relevance, overt reports, and motor responses. Using Bayesian Model Selection, we show that responses reflecting target detection are restricted to secondary somatosensory cortex, whereas activity in insular, cingulate, and motor regions is best explained in terms of stimulus uncertainty and overt reports. Our results emphasise the role of sensory-specific cortex for the emergence of perceptual awareness and dissect the contribution of the frontoparietal network to classical detection tasks.

Decoding vibrotactile choice independent of stimulus order and saccade selection during sequential comparisons.

Decision-making in the somatosensory domain has been intensively studied using vibrotactile frequency discrimination tasks. Results from human and monkey electrophysiological studies from this line of research suggest that perceptual choices are encoded within a sensorimotor network. These findings, however, rely on experimental settings in which perceptual choices are inextricably linked to sensory and motor components of the task. Here, we devised a novel version of the vibrotactile frequency discrimination task with saccade responses which has the crucial advantage of decoupling perceptual choices from sensory and motor processes. We recorded human fMRI data from 32 participants while they performed the task. Using a whole-brain searchlight multivariate classification technique, we identify the left lateral prefrontal cortex and the oculomotor system, including the bilateral frontal eye fields (FEF) and intraparietal sulci, as representing vibrotactile choices. Moreover, we show that the decoding accuracy of choice information in the right FEF correlates with behavioral performance. Not only are these findings in remarkable agreement with previous work, they also provide novel fMRI evidence for choice coding in human oculomotor regions, which is not limited to saccadic decisions, but pertains to contexts where choices are made in a more abstract form.

Conscious access in the near absence of attention: critical extensions on the dual-task paradigm.

Whether conscious perception requires attention remains a topic of intense debate. While certain complex stimuli such as faces and animals can be discriminated outside the focus of spatial attention, many simpler stimuli cannot. Because such evidence was obtained in dual-task paradigms involving no measure of subjective insight, it remains unclear whether accurate discrimination of unattended complex stimuli is the product of automatic, unconscious processing, as in blindsight, or is accessible to consciousness. Furthermore, these paradigms typically require extensive training over many hours, bringing into question whether this phenomenon can be achieved in naive subjects. We developed a novel dual-task paradigm incorporating confidence ratings to calculate metacognition and adaptive staircase procedures to reduce training. With minimal training, subjects were able to discriminate face-gender in the near absence of top-down attentional amplification, while also displaying above-chance metacognitive accuracy. By contrast, the discrimination of simple coloured discs was significantly impaired and metacognitive accuracy dropped to chance-level, even in a partial-report condition. In a final experiment, we used blended face/disc stimuli and confirmed that face-gender but not colour orientation can be discriminated in the dual task. Our results show direct evidence for metacognitive conscious access in the near absence of attention for complex, but not simple, stimuli.This article is part of the theme issue 'Perceptual consciousness and cognitive access'.