María Ruz

High density ERP indices of conscious and unconscious semantic priming.

The existence of differential brain mechanisms of conscious and unconscious processing is a matter of debate nowadays. The present experiment explores whether conscious and unconscious semantic priming in a lexical decision task at a long prime-target stimulus onset asynchrony (SOA) correlate with overlapping or different event related potential (ERP) effects. Results show that the N400 effect, which appeared when words were consciously perceived, completely disappeared when primes were masked at a level where the ability of participants to detect the prime was near chance. Instead, a rather different set of ERP effects was found to index unconscious semantic priming. This suggests that the processes at the basis of conscious and unconscious semantic analyses can under some circumstances be rather different. Moreover, our results support the notion that conscious and unconscious processes are at least partially separable in the brain.

Attention modulates initial stages of visual word processing

Selective attention has the potential to enhance the initial processing of objects, their spatial locations, or their constituent features. The present study shows that this capacity to modulate initial stages of processing also applies to linguistic attributes. A cueing paradigm focused attention at different levels of word representations on a trial-by-trial basis to study the time course of attentional modulation on visual word processing by means of a high-density electrophysiology recording system. Attention to different linguistic attributes modulated components related to semantic, phonological, and orthographic stages of word processing. Crucially, the N200, associated with initial stages of orthographic decoding, was enhanced by attention to the letter pattern of words. These results suggest that top-down attention has the capacity to enhance initial perceptual stages of visual word processing and support the flexibility of attention in modulating different levels of information processing depending on task goals.

Two brain pathways for attended and ignored words

The dependency of word processing on spare attentional resources has been debated for several decades. Recent research in the study of selective attention has emphasized the role of task load in determining the fate of ignored information. In parallel to behavioral evidence, neuroimaging data show that the activation generated by unattended stimuli is eliminated in task-relevant brain regions during high attentional load tasks. We conducted an fMRI experiment to explore how word encoding proceeds in a high load situation. Participants saw a rapid series of stimuli consisting of overlapping drawings and letter strings (words or nonwords). In different blocks, task instructions directed attention to either the drawings or the letters, and subjects responded to immediate repetition of items in the attended dimension. To look at the effect of attention on word processing, we compared brain activations for words and nonwords under the two attentional conditions. As compared to nonwords, word stimuli drove responses in left frontal, left temporal and parietal areas when letters were attended. However, although the behavioral measures suggested that ignored words were not analyzed when drawings were attended, a comparison of ignored words to ignored nonwords indicated the involvement of several regions including left insula, right cerebellum and bilateral pulvinar. Interestingly, word-specific activations found when attended and ignored words were compared showed no anatomical overlap, suggesting a change in processing pathways for attended and ignored words presented in a high attentional load task.

Emotional conflict in interpersonal interactions.

Facial displays of emotions can help to infer the mental states of other individuals. However, the expectations we generate on the basis of peoples emotions can mismatch their actual behaviour in certain circumstances, which generates conflict. In the present study, we explored the neural mechanisms of emotional conflict during interpersonal interactions. Participants had to accept or reject economic offers made by several partners who displayed emotional expressions. On every trial, a cue informed participants of whether they could trust the emotion of their partner or not. Trustworthy (low-conflict) partners with happy facial expressions were cooperative and those with angry expressions did not cooperate. Untrustworthy (high-conflict) partners, on the other hand, cooperated when their expression was angry and did not cooperate when they displayed a happy emotion. Behavioural responses were faster for trustworthy than for untrustworty partners. High-conflict partners activated the anterior cingulate and the anterior insula. In turn, trustworthy partners were associated with activations in the left precuneus. Our results suggest that the emotion displayed by another person affects our decision-making in social contexts. When emotional expressions are linked to their natural consequences, they engage ToM processes. In contrast, untrustworthy emotional expressions engage conflict-related brain regions.

Inattentional Amnesia to Words in a High Attentional Load Task

We investigated the dependence of visual word processes on attention by examining event-related potential (ERP) responses as subjects viewed words while their attention was engaged by a concurrent highly demanding task. We used a paradigm from a previous functional magnetic resonance imaging (fMRI) experiment [Rees, G., Russel, C., Frith, C. D., & Driver, J. Inattentional blindness vs. inattentional amnesia for fixated but ignored words. Science, 286, 25042506, 1999] in which participants attended either to drawings or to overlapping letters (words or nonwords) presented at a fast rate. Although previous fMRI results supported the notion that word processing was obliterated by attention withdrawal, the current electrophysiological results demonstrated that visual words are processed even under conditions in which attentional resources are engaged in a different task that does not involve reading. In two experiments, ERPs for attended words versus nonwords differed in the left frontal, left posterior, and medial scalp locations. However, in contrast to the previous fMRI results, ERPs responded differentially to ignored words and consonant strings in several regions. These results suggest that fMRI and ERPs may have differential sensitivity to some forms of neural activation. Moreover, they provide evidence to restore the notion that the brain analyzes words even when attention is tied to another dimension.

Interactions between perceived emotions and executive attention in an interpersonal game

The emotions displayed by others can be cues to predict their behavior. Happy expressions are usually linked to positive consequences, whereas angry faces are associated with probable negative outcomes. However, there are situations in which the expectations we generate do not hold. Here, control mechanisms must be put in place. We designed an interpersonal game in which participants received good or bad economic offers from several partners. A cue indicated whether the emotion of their partner could be trusted or not. Trustworthy partners with happy facial expressions were cooperative, and angry partners did not cooperate. Untrustworthy partners cooperated when their expression was angry and did not cooperate when they displayed a happy emotion. Event-Related Potential (ERP) results showed that executive attention already influenced the frontal N1. The brain initially processed emotional expressions regardless of their contextual meaning but by the N300, associated to affective evaluation, emotion was modulated by control mechanisms. Our results suggest a cascade of processing that starts with the instantiation of executive attention, continues by a default processing of emotional features and is then followed by an interaction between executive attention and emotional factors before decision-making and motor stages.

Social Information and Economic Decision-Making in the Ultimatum Game

The present study tested how social information about the proposer biases responders’ choices of accepting or rejecting real monetary offers in a classic ultimatum game (UG) and whether this impact is heightened by the uncertainty of the context. Participants in our study conducted a one-shot UG in which their responses had direct consequences on how much money they earned. We used trait-valenced words to provide information about the proposers’ personal characteristics. The results show higher acceptance rates for offers preceded by positive words than for those preceded by negative words. In addition, the impact of this information was higher in the uncertain than in the certain context. This suggests that when deciding whether or not to take money from someone, people take into account what they know about the person they are interacting with. Such non-rational bias is stronger in an uncertain context.

Modulation of neural activity by motivational and spatial biases.

Motivational biases and spatial attention both modulate neural activity and influence behavioural performance. The time course of motivational bias effects, as well as the relationship between motivation and attention across the time course of information processing, however, are relatively unknown. In the present study, event-related potentials (ERPs) were recorded whilst individuals performed a modified Posner task, in which cue stimuli indicated the reward stakes of a given trial and the probable spatial location of a subsequent target stimulus. Reaction times (RTs) were sensitive to motivation and to attention, with faster responses produced on valid and on rewarded trials. In addition, motivation modulated neural activity from the visual analysis of stimuli, with an earlier N1 peak for rewarded compared with non-rewarded stimuli. Effects of motivation were relatively independent from those of attention until late cognitive processing and response production, where motivation and attention interacted to enhance P300-like potentials and the lateralised readiness potential (LRP). The results suggest that multiple sources of modulatory influences may exist, with motivation and attention exerting independent influences over early stimulus and cognitive processing, followed by a late interaction allowing the construction of a comprehensive stimulus representation that contains information pertaining to both motivational and spatial expectations.

Social information and personal interests modulate neural activity during economic decision-making

In the present study we employed electrophysiological recordings to investigate the levels of processing at which positive and negative descriptions of other people bias social decision-making in a game in which participants accepted or rejected economic offers. Besides social information, we manipulated the fairness of the assets distribution, whether offers were advantageous or not for the participant and the uncertainty of the game context. Results show that a negative description of the interaction partner enhanced the medial frontal negativity (MFN) in an additive manner with fairness evaluations. The description of the partner interacted with personal benefit considerations, showing that this positive or negative information only biased the evaluation of offers when they did not favor the participant. P300 amplitudes were enhanced by advantageous offers, suggesting their heightened motivational significance at later stages of processing. Throughout all stages, neural activity was enhanced with certainty about the personal assignments of the split. These results provide new evidence on the importance of interpersonal information and considerations of self-interests relative to others in decision-making situations.

Cognitive and affective control in a flanker word task: common and dissociable brain mechanisms.

In the present study we compared the nature of cognitive and affective conflict modulations at different stages of information processing using electroencephalographic recordings. Participants performed a flanker task in which they had to focus on a central word target and indicate its semantic category (cognitive version) or its valence (affective version). Targets were flanked by congruent or incongruent words in both versions. Although tasks were equivalent at the behavioral level, event-related potentials (ERPs) showed common and dissociable cognitive and emotional conflict modulations. At early stages of information processing, both tasks generated parallel sequential conflict effects in the P1 and N170 potentials. Later, the N2 and the first part of the P3 wave were exclusively modulated by cognitive conflict, whereas the last section of the P3 deflection/Late Positive Component (LPC) was only involved in affective current conflict processing. Therefore, the whole data set suggests the existence of early common mechanisms that are equivalent for cognitive and affective materials and later task-specific conflict processing.