Neurophysiology of Active Perception

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===== Who controls the attentional enhancement of targets, the blocking of distracters, and the resolution of conflict? ===== One of the things that distinguishes humans from lower animals is their ability to select task-relevant information in cluttered sensory environments. This ability goes beyond merely selecting the information to which one has to respond; it also involves the ability to deal with the conflict that emerges when multiple stimuli elicit incompatible responses. Initially, this situation of response conflict results from insufficient selection between the different stimuli but, following the detection of response conflict, it may also be resolved by increasing the selectivity (i.e., enhancing task-relevant information and blocking distractors). Therefore, it is no surprise that one of the central questions in cognitive neuroscience is how the brain allows for goal-directed behaviour by the selective gating of sensory information, depending on task-relevance. Although it is clear that selective attention plays a role in target enhancement, distracter blocking, and the resolution of conflict, little is know about the brain areas that control these processes. The dominant view here is that frontal cortical areas are responsible for this, and this view is consistent with the fact that fMRI studies of attentional control and conflict monitoring show a robust involvement of these frontal cortical areas, with lateral areas mainly involved in attentional orienting, and medial areas (i.c., the anterior cingulate) mainly involved in conflict monitoring. However, this view is based on studies with important limitations: - The studies that investigated attentional control studies did not allow to distinguish between target enhancement and distractor blocking. - The studies that investigated conflict monitoring used very short trials in which several processes could easily be confounded (conflict detection and its resolution via inhibition, target enhancement, and distracter blocking). In this study, we will identify the brain areas that control target enhancement, distracter blocking, and conflict Compared to fMRI studies, there is only limited evidence from electrophysiological studies showing the involvement of frontal cortical areas in the modulation of neural oscillations over sensory input areas. Two recent magnetoencephalography studies are exceptions to this rule ([[http://www.sciencemag.org/content/344/6182/424.short|Baldauf & Desimone, 2014]]; [[http://www.jneurosci.org/content/35/5/2074.short|Sacchet et al, 2015]]), and both found evidence for oscillatory coupling between the right inferior frontal cortex (rIFG) and different sensory areas (S1 in Sacchet et al, 2015; fusiform face area and parahippocampal place area in Baldauf & Desimone, 2014). A dominant view is that neural oscillations play a central role in this gating of sensory information. This starts from the common observation of alpha band (8-14 Hz) oscillations over posterior (occipito-parietal) areas and alpha- and beta band (15-25 Hz) oscillations over sensorimotor areas. With respect to the functional role of these oscillations, the dominant view involves that high amplitude neural oscillations block the sensory input (visual for the posterior and somatosensory for the sensorimotor areas) whereas low amplitude neural oscillations allow the sensory input to be transferred to downstream areas. It is surprising how little behavioural evidence there is for this claim, and the goal of this project proposal is to provide such evidence. At the end, for cognitive neuroscience, the only relevant neural parameters are those that are systematically related to cognition and behaviour. We will conduct a study in the visual modality, and this will allow us to investigate the relationship between alpha band oscillations over posterior areas and (1) behaviour (accuracy and reaction time), and (2) neural markers of motor preparation recorded over motor areas. We will analyse these relations over trials (instead of over participants), as this analysis will reveal patterns that do not depend on individual differences. In our experiment, the participant fixates the center of the screen while stimulus streams are presented in the left and the right visual field. The participant responds using two buttons, one for his left and one for his right hand. One of the two buttons has to be pressed depending on the content of the attended stimulus streams, as explained in the following. By means of a cue, one of these two streams will be indicated as the task-relevant one, and the other one will be the distracter. The streams are continuously present but their content varies over time. The content are symbols belonging to one of three different categories associated with the button press: //press left//, //press right//, and //don't press//. The participant's task is to respond as quickly as possible when a //press left// or a //press right// symbol shows up in the attended stream. By shortening the presentation time and by means of feedback, response speed will be stressed, thereby increasing the probability of an error. The data will be analyzed by first selecting relevant fixed-length epochs from the electrophysiological data: (1) epochs centered at stimulus events in which **one** of the streams shows a //press// symbol, separately for the attended and the non-attended stream, and (2) epochs centered at stimulus events in which **both** of the streams show a //press// symbol, separately for congruent (same response button indicated) and incongruent (different response buttons indicated) symbol pairs. This produces four conditions that will be compared on the combined behavioural-electrophysiological data. To investigate the role of visual alpha oscillations in the gating of sensory information, we will relate the pre-event visual alpha oscillations with the following post-event variables: - The behavioural response (accuracy and reaction time) to single //press// symbols in the attended stream only. - The neural response (in particular, the inhibitory response over the motor cortex) to single //press// symbols in the ignored stream only. - The behavioural and neural response to dual (in both streams) incongruent (conflicting) //press// symbols, which are to be compared to the responses to dual congruent //press// symbols. The relation between the pre-event visual alpha oscillations and the behavioural and neural responses to single //press// events will inform us about the oscillation's gating function in the context of single task-relevant or distracting stimuli. The same relation, but now investigated in epochs that involve dual //press// symbols will inform us about the oscillation's gating function in the context of conflicting stimuli. This project will be supervised by Eric Maris.