‘Selective attention’ describes our ability to focus processing resources on particular aspects of our internal or external environment, whilst disregarding others (for example, concentrating on a specific conversation at a party, whilst ignoring other conversations, the music, etc.). What factors drive attentional selection? A broad distinction can be made between the exogenous (bottom-up) ‘capture’ of attention and the endogenous (top-down), voluntary steering of attention. Top-down attention mechanisms can further be broken down into ‘spatial attention’ and ‘feature-based attention’. The former describes the ability to voluntarily focus one’s attention on a particular region in space (even without moving one’s eyes towards that location), and the latter describes the ability to focus on particular visual features of the environment, for example on a particular color or shape. Bottom-up driven attention refers to the quasi-automatic capture of spatial attention by physically conspicuous (salient) stimuli, such as moving stimuli, and stimuli of high local luminance contrast (e.g. a red flower on a green meadow).

Bottom-up mechanisms of attentional capture have evolved to alert us to potentially important (harmful or helpful) stimuli in our environment. However, if attention were solely driven in a bottom-up manner, we would find it impossible to achieve goal-directed behavior, since we would constantly have our attention distracted by external stimuli. Thankfully, we have the ability to employ top-down attention mechanisms to steer attention towards stimuli that we deem important for reasons other than their physical conspicuity. This allows us, for instance, to read a book when sitting at a bus stop, while ignoring the ongoing traffic in front of us. However, it would be similarly detrimental if attention were governed exclusively by top-down factors: even when concentrating hard on our book, our attention still needs to be susceptible to highly salient bottom-up stimulation, such as a crashing car in front of us (or the bus arriving). Thus, a fine balance between externally and internally driven attention is crucial for successfully navigating through life, and an imbalance between these mechanisms may lie at the root of some psychopathologies, such as Attention Deficit Disorder. Importantly, bottom-up and top-down mechanisms of attention are interactive, that is, the effect of one depends on the current state of the other. For instance, the effectiveness of a particular stimulus in attracting our attention in a bottom-up manner depends on the current ‘settings’ of top-down spatial and feature-based attention. If you are searching for lemons at the grocery store, other small yellow objects are liable to capture your attention more than little red objects. If you were looking for tomatoes, the opposite would hold.

We are interested in elucidating the neural mechanisms that mediate the interaction between bottom-up and top-down influences on selective attention, particularly within the visual domain. Specifically, we combine functional magnetic resonance imaging (fMRI) and eye-tracking with experimental paradigms that typically require the participant to detect or find (and categorize) a ‘target’ stimulus among other, non-target stimuli (i.e., visual search). In these paradigms, we can manipulate the nature of bottom-up stimulus salience of the target and non-target stimuli, on the one hand, and the degree and type (spatial, feature-based) of top-down (cue) information that is available to the participant prior to the search, on the other hand. Evidently, the strategic use of cue information to guide attention in these experiments is also relevant to our interest in cognitive control mechanisms. Furthermore, we are interested in the functional interactions between brain regions that mediate attentional orienting and brain regions that are involved in motivating these shifts of attention in real life, such as limbic areas that are responsible for appraising the motivational significance of external stimuli. This work is another example of investigating interactions between attention and ‘emotional’ processes, and has close overlap with our interest in affective control mechanisms.