Neurophysiology of Active Perception

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===== Do we slow down when we get conflicting information ? ===== 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 may result 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. Conflict monitoring is a set of cognitive processes that allows us to deal with conflict between different stimuli in our environment, but also between internal factors such as desire and fear. In this project, we will focus on the former type, conflict between different stimuli that are associated with different behavioural responses. A well accepted behavioural index of conflict monitoring is the so-called //conflict effect//: the reaction time (RT) difference between stimulus configurations in which the components elicit different responses (incongruent stimuli) and stimulus configurations in which the components elicit the same response (congruent stimuli). The typical observation is that the RT to incongruent stimuli is larger than the one to the congruent stimuli. This has been observed in several tasks, such as the [[https://en.wikipedia.org/wiki/Eriksen_flanker_task|flanker]], the [[https://en.wikipedia.org/wiki/Stroop_effect|Stroop]] and the [[https://en.wikipedia.org/wiki/Simon_effect|Simon]] task, each of which involves a different stimulus configuration. From the conflict effect, it has been concluded that the monitoring of response conflict (i.c., its detection and subsequent resolution) is an automatic process, triggered by stimulus incongruency. However, to my knowledge, there is no conclusive evidence for the automaticity of this process. As an alternative hypothesis, I put forward that people can typically often make use of spatial attention to prevent response conflict. Therefore, I predict that, when spatial attention is deployed to one of the stimulus components, the conflict effect is no longer observed. To investigate this hypothesis, we will use a novel experimental paradigm that extends and improves on existing paradigms. In this experimental, the participant fixates a dot at the centre of the screen while stimulus streams are presented in the left and the right visual field. These streams are composed of stimuli that change continuously over the course of time. There are two stimulus categories, and here we assume they are letters and digits. The participant responds using two buttons, one for his left and one for his right hand. Each of the two buttons is associated to one stimulus category (letters or digits), and the participant has to press this button when the fixation dot increases size (the so-called go-signal). A snapshot of an example stimulus stream is shown in Figure 1. Over the course of time, the stimulus streams change, with letters being replaced by digits or other letters, and vice versa for digits that are being replaced. {{:slide07.jpg?400 |Snapshot of example stimulus stream}} At any point in time, one of the two stimulus streams is the relevant one: it indicates the hand (left or right) with which the participant must press the corresponding button after the go-signal (an increase in the size of the fixation dot). The relevant stimulus stream is indicated by the colour of the fixation dot, for example, with yellow denoting left and blue denoting right. Because the response hand indicated by the attended stimulus stream changes over time, so does the participant’s preparation, and this requires a continuous engagement over the course of a trial. The trial length is determined by the time between stream onset and go-signal, and this period may contain several alternations between left and right hand preparation. This mimics the continuous changes in sensory input in daily life. However, this experimental paradigm does not mimic daily life with respect to the continuous changes in the location of the relevant stimulus. In fact, depending on the colour of the fixation dot (the attentional cue), either the left or the right visual stream would be the relevant one in the course of the whole trial. Therefore, to force the participant to shift his attention to a continuously varying location, we continuously varied the colour of the fixation dot between yellow and blue. By continuously varying the attentional cue, we continuously change the side to which spatial attention is directed. The largest uncertainty about where attention should be directed is when the fixation dot’s colour is exactly halfway between yellow and blue (i.e., green). In combination with an incongruent stimulus pair (a letter and digit), the distance between a given colour and the colour green (along the yellow-blue colour line), is an index of response competition. We will use this stimulus type to investigate our hypothesis that the conflict effect is no longer observed when spatial attention is deployed to one of the stimulus stream. More specifically, we predict the following: - When attention is directed exclusively to one of the two stimulus streams, there will be no conflict effect (i.e., no difference between congruent and incongruent stimulus streams). - When attention not directed to either of the two stimulus, the conflict effect will be maximal. This project will be supervised by Eric Maris.