Neural mechanisms of top-down control during visual search: effects of template complexity

Neural mechanisms of top-down control during visual search: effects of template complexit

Multi-level agent-based modeling with the Influence Reaction principle

This paper deals with the specification and the implementation of multi-level agent-based models, using a formal model, IRM4MLS (an Influence Reaction Model for Multi-Level Simulation), based on the Influence Reaction principle. Proposed examples illustrate forms of top-down control in (multi-level) multi-agent based-simulations

The relationship between childhood aerobic fitness and brain functional connectivity

AbstractSeveral studies have indicated that higher levels of childhood aerobic fitness is associated with superior cognitive function, and this association is disproportionately observed in tasks requiring greater top-down control. We designed the current study to clarify the relationship between childhood fitness and top-down control in terms of functional connectivity among brain regions, by evaluating phase-locking values (PLVs), which is a measure of frequency-specific phase synchrony between electroencephalographic signals during a visual search task. Lower-fit and higher-fit children performed a visual search task that included feature search and conjunction search conditions. The conjunction search condition required greater top-down control to reduce interference from task-irrelevant distractors that shared a basic feature with the target. Results indicated that higher-fit children exhibited higher response accuracy relative to lower-fit children across search conditions. The results of PLVs showed that higher-fit children had greater functional connectivity for the conjunction relative to the feature search condition, whereas lower-fit children showed no difference in functional connectivity between search conditions. Furthermore, PLVs showed different time courses between groups; that is, higher-fit children sustained upregulation of top-down control throughout the task period, whereas lower-fit children transiently upregulated top-down control after stimulus onset and could not sustain the upregulation. These findings suggest that higher levels of childhood aerobic fitness is related to brain functional connectivity involved in the sustained upregulation of top-down control

Frontal top-down signals increase coupling of auditory low-frequency oscillations to continuous speech in human listeners

Humans show a remarkable ability to understand continuous speech even under adverse listening conditions. This ability critically relies on dynamically updated predictions of incoming sensory information, but exactly how top-down predictions improve speech processing is still unclear. Brain oscillations are a likely mechanism for these top-down predictions [1 and 2]. Quasi-rhythmic components in speech are known to entrain low-frequency oscillations in auditory areas [3 and 4], and this entrainment increases with intelligibility [5]. We hypothesize that top-down signals from frontal brain areas causally modulate the phase of brain oscillations in auditory cortex. We use magnetoencephalography (MEG) to monitor brain oscillations in 22 participants during continuous speech perception. We characterize prominent spectral components of speech-brain coupling in auditory cortex and use causal connectivity analysis (transfer entropy) to identify the top-down signals driving this coupling more strongly during intelligible speech than during unintelligible speech. We report three main findings. First, frontal and motor cortices significantly modulate the phase of speech-coupled low-frequency oscillations in auditory cortex, and this effect depends on intelligibility of speech. Second, top-down signals are significantly stronger for left auditory cortex than for right auditory cortex. Third, speech-auditory cortex coupling is enhanced as a function of stronger top-down signals. Together, our results suggest that low-frequency brain oscillations play a role in implementing predictive top-down control during continuous speech perception and that top-down control is largely directed at left auditory cortex. This suggests a close relationship between (left-lateralized) speech production areas and the implementation of top-down control in continuous speech perception

Voluntary task switching under load: contribution of top-down and bottom-up factors in goal-directed behavior

The present study investigated the relative contribution of bottom-up and top-down control to task selection in the voluntary task-switching (VTS) procedure. In order to manipulate the efficiency of top-down control, a concurrent working memory load was imposed during VTS. In three experiments, bottom-up factors, such as stimulus repetitions, repetition of irrelevant information, and stimulus task associations, were introduced in order to investigate their influence on task selection. We observed that the tendency to repeat tasks was stronger under load, suggesting that top-down control counteracts the automatic tendency to repeat tasks. The results also indicated that task selection can be guided by several elements in the environment, but that only the influence of stimulus repetitions depends on the efficiency of top-down control. The theoretical implications of these findings are discussed within the interplay between top-down and bottom-up control that underlies the voluntary selection of tasks

Top-Down Control of Lateral Interactions in Visual Cortex

V1 neurons are capable of integrating information over a large area of visual field. Their responses to local features are dependent on the global characteristics of contours and surfaces that extend well beyond their receptive fields. These contextual influences in V1 are subject to cognitive influences of attention, perceptual task and expectation. Previously it’s been shown that the response properties of V1 neurons change to carry more information about behaviorally relevant stimulus features (Li et al. 2004). We hypothesized that top-down modulation of effective connectivity within V1 underlies the behaviorally dependent modulations of contextual interactions in V1. To test this idea, we used a chronically implanted multi-electrode array in awake primates and studied the mechanisms of top-down control of contextual interactions in V1. We used a behavioral paradigm in which the animals performed two different perceptual tasks on the same stimulus and studied task-dependent changes in connectivity between V1 sites that encode the stimulus. We found that V1 interactions-both spiking and LFP interactions-showed significant task-dependent changes. The direction of the task-dependent changes observed in LFP interactions, measured by coherence between LFP signals, was dependent on the perceptual strategy used by the animal. Bisection task involving perceptual grouping of parallel lines increased LFP coherence while vernier task involving segregation of collinear line decrease LFP coherence. Also, grouping of collinear lines to detect a contour resulted in increased LFP interactions. Since noise correlations can affect the coding accuracy of a cortical network, we investigated how top-down processes of attention and perceptual task affect V1 noise correlations. We were able to study the noise correlation dynamics that were due to attentional shift separately from the changes due to the perceptual task being performed at the attended location. Top-down influences reduced V1 noise-correlations to a greater extent when the animal performed a discrimination task at the recorded locations compared to when the animal shifted its attention to the location. The reduction in noise correlation during the perceptual task was accompanied by a significant increase in the information carried about the stimulus (calculated as Fisher information). Our analysis was also able to determine the degree to which the task dependent change in information was due to the alteration in neuronal tuning compared to changes in correlated activity. Interestingly, the largest effects on information were seen between stimuli that had the greatest difficulty of discrimination

Task-specific effects of reward on task switching

Although cognitive control and reinforcement learning have been researched extensively over the last few decades, only recently have studies investigated their interrelationship. An important unanswered question concerns how the control system decides what task to execute and how vigorously to carry out the task once selected. Based on a recent theory of control formulated according to principles of hierarchical reinforcement learning, we asked whether rewards can affect top-down control over task performance at the level of task representation. Participants were rewarded for correctly performing only one of two tasks in a standard task-switching experiment. Reaction times and error rates were lower for the reinforced task compared to the non-reinforced task. Moreover, the switch cost in error rates for the non-reinforced task was significantly larger compared to the reinforced task, especially for trials in which the imperative stimulus afforded different responses for the two tasks, resulting in a "non-paradoxical" asymmetric switch cost. These findings suggest that reinforcement at the task level resulted in greater application of top-down control rather than in stronger stimulus-response pathways for the rewarded task