Decoding Human Visual Colour EEG Information Using Machine Learning and Visual Evoked Potentials

With the rapid development of brain-computer interfaces (BCIs), human visual decoding, one of the important research directions of BCIs, has attracted a substantial amount of attention. However, most visual decoding studies have focused on graphic and image decoding. In this paper, we first demonstrate the possibility of building a new kind of task-irrelevant, simple and fast-stimulus BCI-based experimental paradigm that relies on visual evoked potentials (VEPs) during colour observation. Additionally, the features of visual colour information were found through reliable real-time decoding. We selected 9 subjects who did not have colour blindness to participate in our tests. These subjects were asked to observe red, green, and blue screens in turn with an interstimulus interval of 1 second. The machine learning results showed that the visual colour classification accuracy had a maximum of 93.73%. The latency evoked by visual colour stimuli was within the P300 range, i.e., 176.8 milliseconds for the red screen, 206.5 milliseconds for the green screen, and 225.3 milliseconds for the blue screen. The experimental results hereby show that the VEPs can be used for reliable colour real-time decoding.

EMOSEX – emotion prevails over sex during implicit judgment of faces

Appraisals can be influenced by cultural beliefs and stereotypes. In line with this, past research has shown that judgments about the emotional expression of a face are influenced by the face’s sex, and vice versa that judgments about the sex of a person somewhat depend on the person’s facial expression. For example, participants associate anger with male faces, and female faces with happiness or sadness. However, the strength and the bidirectionality of these effects remain debated. Moreover, the interplay of a stimulus’ emotion and sex remains mostly unknown in the auditory domain. To investigate these questions, we created a novel stimulus set of 121 avatar faces and 121 human voices (available at https://bit.ly/2JkXrpy) with matched, fine-scale changes along the emotional (happy to angry) and sexual (male to female) dimensions. In a first experiment (N=76), we found clear evidence for the mutual influence of facial emotion and sex cues on ratings, and moreover for larger implicit (task-irrelevant) effects of stimulus’ emotion than of sex. These findings were replicated and extended in two preregistered studies – one laboratory categorisation study using the same face stimuli (N=108; https://osf.io/ve9an), and one online study with vocalisations (N=72; https://osf.io/vhc9g). Overall, results show that the associations of maleness-anger and femaleness-happiness exist across sensory modalities, and suggest that emotions expressed in the face and voice cannot be entirely disregarded, even when attention is mainly focused on determining stimulus’ sex. We discuss the relevance of these findings for cognitive and neural models of face and voice processing.

Deciding on Optical Illusions: Reduced Alpha Power in Body Dysmorphic Disorder

Background: Body dysmorphic disorder (BDD) is a psychiatric disorder characterized by excessive preoccupation with imagined defects in appearance. Optical illusions induce illusory effects that distort the presented stimulus thus leading to ambiguous percepts. Using electroencephalography (EEG), we investigated whether BDD is related to differentiated perception during illusory percepts. Methods: 18 BDD patients and 18 controls were presented with 39 optical illusions together with a statement testing whether or not they perceived the illusion. After a delay period, they were prompted to answer whether the statement is right/wrong and their degree of confidence for their answer. We investigated differences of BDD on task performance and self-reported confidence and analysed the brain oscillations during decision-making using nonparametric cluster statistics. Results: Behaviorally, the BDD group exhibited reduced confidence when responding incorrectly, potentially attributed to higher levels of doubt. Electrophysiologically, the BDD group showed significantly reduced alpha power at mid-central scalp areas, suggesting impaired allocation of attention. Interestingly, the lower the alpha power of the identified cluster, the higher the BDD severity, as assessed by BDD psychometrics. Conclusions: Results evidenced that alpha power during illusory processing might serve as a quantitative EEG biomarker of BDD, potentially associated with reduced inhibition of task-irrelevant areas.

The rosy future paradox: Positive future thinking without task relevance enhances negative biases and anxiety for aversive events

Expectations have an important role in guiding behavior and the interpretation of novel information, but can contain negative biases such as is the case in anxiety disorders. Positive future thinking may provide an accessible way to attenuate these negatively biases. However, much is still unclear about the optimal form of such positive interventions, and it is unknown if the effects go beyond subjective experience. Here, we used a positive future thinking intervention to adapt the way a stressful event is experienced. Participants imagined either task-relevant (N = 21) or irrelevant (N = 21) positive future events before being subjected to the Trier Social Stress Task, or did not receive the intervention (N= 20). We recorded resting state EEG during the anticipation and recovery phases of the TSST to assess intervention and trait anxiety related differences in the level of frontal delta-beta coupling, which is considered a neurobiological substrate of emotion regulation. Results show that the intervention reduces event-related stress and anxiety, and increases social fixation behavior and task performance, but only if future thinking is task relevant. Paradoxically, task-irrelevant positive future thoughts enhance negative perceptual biases and stress reactivity. This increase in stress reactivity in the task-irrelevant group was corroborated by the elevated levels frontal delta-beta coupling during event anticipation, especially for those with high trait anxiety. This suggests an increased demand for emotion regulation following the task-irrelevant intervention, possibly due to the contextual incongruence between positive imagery and the stressor. Together, these results show that positive future thinking can mitigate the negative emotional, behavioral and neurobiological consequences of a stressful event, but that it should not be applied indiscriminately. Task-relevant positive future thinking can be an accessible way to boost efficacy of exposure therapy for pathological anxiety, and can help people deal with negative anticipation in daily life.

Reward priming differentially modulates enhancement and inhibition in auditory decision-making

In cognitive sciences, rewards, such as money and food, play a fundamental role in individuals' daily lives and well-being. Moreover, rewards that are irrelevant to the task alter individuals' behavior. However, it is unclear whether explicit knowledge of reward irrelevancy has an impact on reward priming enhancements and inhibition. In this study, an auditory change-detection task with task-irrelevant rewards was introduced. The participants were informed explicitly in advance that the rewards would be given randomly. The results revealed that while inhibition related to reward priming only occurred when the participants were explicitly informed about rewards, implicit instruction thereof resulted in enhancement and inhibition associated with reward priming. These findings highlight the contribution of explicit information about rewards associated with auditory decisions.

Belief in Control: Voluntary Choice Enhances Subsequent Task Performance under Undefeated Choice-Outcome Causation

Humans are believed to have volition through which they act upon and change the external environment. As an exercise of volition, making a voluntary choice facilitates the subsequent behavioral performance relative to a forced choice. However, it is unclear how this facilitation is constrained by the perceived relationship between a choice and its outcome. In a series of experiments, participants were free or forced to choose one of two presented pictures. The outcome of the choice was then revealed, which could be always the chosen picture or always the unchosen picture (i.e., a confirmed choice-outcome causation), a blank screen with no picture at all (i.e., an unrevealed choice-outcome relation), the chosen or unchosen picture with equal probability (i.e., a defeated choice-outcome causation), or a third picture different from the two preceding options (again, a defeated choice-outcome causation). Participants then complete a visual search task with the task-irrelevant picture (or the blank screen) serving as a background. Results showed that the search performance was improved after a voluntary choice under both the confirmed causation and the unrevealed relation, but not under the defeated causation. Over individuals, the improved performance due to voluntary choice under confirmed causation positively correlated with the improved performance under the unrevealed relation, and with the reported belief in controlling the outcome of the choice. Our findings suggest that the exercise of volition motivates subsequent behavior, and this motivation is restricted to an “undefeated” choice-outcome causation which affords a belief in controlling the outcome by exerting volition.

Neural Indices of Emotional Distraction

<p>Emotional stimuli capture our attention. The preferential processing of emotional information is an adaptive mechanism that when relevant to our goal highlights potentially important aspects in the environment. However, when emotional information is task-irrelevant, their presence in the environment can trigger involuntary shifts in attention that cause detriments to performance. One challenge to investigating emotional distraction in the lab is how to objectively investigate the allocation of attention between different elements on the same stimulus display (e.g. between the task and the distractors). One neural measure that overcomes this issue is the Steady-State-Visual-Evoked-Potential (SSVEP). An SSVEP is the neural response of the visual cortex to a flickering stimulus and can be used as a measure of attentional resource allocation (Norcia, Appelbaum, Ales, Cottereau, & Rossion, 2015). In the past, emotional distraction has been studied using spatially separated tasks and distractors. The current thesis presents two experiments using SSVEPs to investigate emotional distraction in a superimposed design. Experiment 1 aimed to conceptually replicate Hindi Attar and colleagues (2010) who developed an SSVEP emotional distraction paradigm to examine attentional resource allocation between background task-irrelevant emotional distractors and a foreground dot-motion task. Participants viewed a stimulus display of moving, flickering dots, while positive or neutrally valanced distractors (or unidentifiable scrambles) were presented in the background of the task. SSVEPs were reduced in the presence of positive intact compared to neutral intact distractors suggesting that the presentation of task-irrelevant emotional stimuli in the same spatial location as a foreground task initiates an involuntary shift of attention away from the task. Unexpectedly, in both Experiments 1 and 2 valence differences were found in SSVEPs between positive and neutral scrambled images; this suggests that there are some perceptual differences between the stimulus sets (e.g. colour) contributing to the drop in SSVEP found for positive intact images. Importantly, in the SSVEP analysis significant valence x image type interactions were found, demonstrating that the drop for positive images was stronger for intact than scrambled image conditions, suggesting that a significant amount of the drop in SSVEP was driven by a difference in valence between the intact distractors. Behavioural results also suggest evidence for emotional distraction through reduced hit rate in the presence of positive intact images compared to neutral intact images in Experiment 1, and reduced detection sensitivity and response criterion for positive intact images in Experiment 2. Overall, the current thesis demonstrates support for the hypothesis that emotional information is more distracting than neutral information and provides a valuable starting point for the examination of emotion attention interactions when the task and distractors share the same location. Future studies could use SSVEPs to examine neural processing differences between emotional and neutral scrambled images.</p>

Learning to Expect the Predictable: The Role of Expectation in the Cognitive Control of Attention

<p>Some of the visual world is relevant to our goals and needs. Much more is not. A problem we face frequently in day-to-day living is that we are distracted by what is not relevant to our goals at the cost of attention towards what is. Emotional stimuli in particular have been shown to be very effective distractors, out-competing task-relevant stimuli for our attentional resources (Carretié, 2014; Pessoa, 2005; Pourtois et al., 2013). How often emotional distractors occur can alter our ability to ignore them and remain task focussed (Grimshaw et al., 2018; Schmidts et al., 2020). The Dual Mechanisms of Control framework (Braver et al., 2007; Braver, 2012) suggests that, because we can expect upcoming distractors when they occur frequently, we can effectively avoid distraction through proactive control; the use of effortful preparatory cognitive control strategies. That said, when distractors are frequent, we also become more experienced with them, and resolving the attentional conflict they create. The present investigation spanned two experiments assessing whether expectation of upcoming distractors would elicit proactive control while holding the experience of previous distractors constant. In Experiment 1 participants performed a simple perceptual task at fixation while neutral or negative task irrelevant images appeared peripherally on 25% of trials, either predictably in sequence (every fourth trial) or randomly. Expectation of distraction did not improve participants’ ability to avoid emotional distraction. A paradoxical expectation effect was also found wherein distraction was increased rather than decreased when distractors occurred predictably. In Experiment 2 distractors appeared either predictably (every fourth trial), on a random 25% of trials, or on a random 75% of trials. However, neutral and emotional images were now presented at fixation with the perceptual task presented above and below. Greater distractor frequency led to lower distraction and expectation of upcoming distractors again did not improve control, although a paradoxical increase in distraction was not replicated. Findings indicate that expectation of upcoming distractors alone is not sufficient to drive individuals to implement proactive control. Rather, distractor frequency is suggested to drive proactive control through implicit changes in top-down control settings based on experience. While the processes behind experience-driven proactive control are unclear, conflict adaptation and selection history are discussed as possible mechanisms of experience driven proactive control. Critically, present findings also indicate that emotional stimuli may present a unique challenge to our ability to control our attention.</p>