Brain and Cognition Research Center

Identifying factors whose fluctuations are associated with choice inconsistency is a major issue for rational decision theory. Here, we investigated the neuro-computational mechanisms through which mood fluctuations may bias human choice behavior. Intracerebral EEG data were collected in a large group of subjects (n=30) while they were performing interleaved quiz and choice tasks that were designed to examine how a series of unrelated feedbacks affect decisions between safe and risky options. Neural baseline activity preceding choice onset was confronted first to mood level, estimated by a computational model integrating the feedbacks received in the quiz task, and then to the weighting of option attributes, in a computational model predicting risk attitude in the choice task. Results showed that (1) elevated broadband gamma activity (BGA) in the ventromedial prefrontal cortex (vmPFC) and dorsal anterior insula (daIns) was respectively signaling periods of high and low mood, (2) increased vmPFC and daIns BGA respectively promoted and tempered risk taking by overweighting gain vs. loss prospects. Thus, incidental feedbacks induce brain states that correspond to different moods and bias the evaluation of risky options. More generally, these findings might explain why people experiencing positive (or negative) outcome in some part of their life tend to expect success (or failure) in any other.

Multisensory facilitation is known to improve the perceptual performances and reaction times of participants in a wide range of tasks, from detection and discrimination to memorization. We asked whether a multimodal signal can similarly improve action inhibition using the stop–signal paradigm. Indeed, consistent with a crossmodal redundant signal effect that relies on multisensory neuronal integration, the threshold for initiating behavioral responses is known for being reached faster with multisensory stimuli. To evaluate whether this phenomenon also occurs for inhibition, we compared stop signals in unimodal (human faces or voices) versus audiovisual modalities in natural or degraded conditions. In contrast to the expected multisensory facilitation, we observed poorer inhibition efficiency in the audiovisual modality compared with the visual and auditory modalities. This result was corroborated by both response probabilities and stop–signal reaction times. The visual modality (faces) was the most effective. This is the first demonstration of an audiovisual impairment in the domain of perception and action. It suggests that when individuals are engaged in a high–level decisional conflict, bimodal stimulation is not processed as a simple multisensory object improving the performance but is perceived as concurrent visual and auditory information. This absence of unity increases task demand and thus impairs the ability to revise the response.

Here, we provide an analysis of the microsaccades that occurred during continuous visual search and targeting of small faces that we pasted either into cluttered background photos or into a simple gray background. Subjects continuously used their eyes to target singular 3-degree upright or inverted faces in changing scenes. As soon as the participant’s gaze reached the target face, a new face was displayed in a different and random location. Regardless of the experimental context (e.g. background scene, no background scene), or target eccentricity (from 4 to 20 degrees of visual angle), we found that the microsaccade rate dropped to near zero levels within only 12 milliseconds after stimulus onset. There were almost never any microsaccades after stimulus onset and before the first saccade to the face. One subject completed 118 consecutive trials without a single microsaccade. However, in about 20% of the trials, there was a single microsaccade that occurred almost immediately after the preceding saccade’s offset. These microsaccades were task oriented because their facial landmark targeting distributions matched those of saccades within both the upright and inverted face conditions. Our findings show that a single feedforward pass through the visual hierarchy for each stimulus is likely all that is needed to effectuate prolonged continuous visual search. In addition, we provide evidence that microsaccades can serve perceptual functions like correcting saccades or effectuating task-oriented goals during continuous visual search.

Deep Reinforcement Learning has demonstrated the potential of neural networks tuned with gradient descent for solving complex tasks in well-delimited environments. However, these neural systems are slow learners producing specialized agents with no mechanism to continue learning beyond their training curriculum. On the contrary, biological synaptic plasticity is persistent and manifold, and has been hypothesized to play a key role in executive functions such as working memory and cognitive flexibility, potentially supporting more efficient and generic learning abilities. Inspired by this, we propose to build networks with dynamic weights, able to continually perform self-reflexive modification as a function of their current synaptic state and action-reward feedback, rather than a fixed network configuration. The resulting model, MetODS (for Meta-Optimized Dynamical Synapses) is a broadly applicable meta-reinforcement learning system able to learn efficient and powerful control rules in the agent policy space. A single layer with dynamic synapses can perform one-shot learning, generalizes navigation principles to unseen environments and manifests a strong ability to learn adaptive motor policies.

When the eyes move or a target moves, the target may be perceived at its predicted next location, displaced from its current retinal location. We hypothesised that this predictive mechanism is controlled by saccade maps found, for example, within the frontal eye fields (FEF) and the intraparietal sulcus (IPS). We examined whether repetitive transcranial magnetic stimulation (rTMS) over right FEF, right IPS, and a control site, peripheral V1/V2, diminished participants' perception of two cases of predictive position perception: trans-saccadic fusion, and the flash grab illusion. In trans-saccadic fusion, participants saccade toward a stimulus that is replaced with another stimulus at the same spatial location when the saccade lands, this frequently leads to a fused percept of both stimuli as if they had been presented together at the same location (Paeye, Collins, & Cavanagh, VSS2016). There was a main effect of rTMS condition on the frequency of trans-saccadic fusion (F(3,11)4.25, p=0.012) within 10 minutes of rTMS stimulation. rTMS to IPS led to a decrease in the frequency of trans-saccadic fusion reports in comparison to the no-TMS conditions (t(11)=3.8480,p=0.0027) and to rTMS to the control site (t(11)=3.3192,p=0.0068). rTMS to FEF also reduced the frequency of trans-saccadic fusion reports although not significantly (compared to no-TMS p=0.059, compared to control rTMS p=0.091). rTMS to the control site did not affect trans-saccadic fusion (p=0.6592). In the flash-grab illusion, a bar is flashed on a moving background leading to the percept that the bar has shifted in the direction of the motion after the flash (Cavanagh & Anstis, 2013). In contrast to the trans-saccadic fusion results, the reduction in the flash grab illusion after rTMS to IPS and FEF did not reach significance (p=0.6004.) These findings suggest that right IPS contains saccade maps that contribute to predictive position perception during trans-saccadic fusion. Meeting abstract presented at VSS 2016