The role of the frontopolar cortex in the exploratory redistribution of attentional resources

Abstract

The successful navigation in rapidly changing environments heavily relies on focus- ing on what is important while ignoring the irrelevant. Attention helps us doing this by supporting the facilitated processing of relevant information, often automatically and governed by implicit motives. At the same time, changing circumstances leave us being confronted with the need to adjust our behavior. Such adaptation requires a redistribution of attentional resources towards a new strategy or goal. Although neuroimaging evidence could link the anterior prefrontal, specifically the frontopo- lar cortex (FPC), to exploratory re-weighting of attentional weights, we only have started to unravel the neurocognitive mechanisms that help us to find a balance be- tween continuing to do what we know works for us and trying something new. The series of experiments presented in this dissertation was designed to investigate the role of FPC in exploratory shifts of attention. In the first experiment, a novel behav- ioral masking paradigm was designed to test if shifts of feature-based attention can occur in response to fully invisible stimulus changes in young healthy human par- ticipants. The second experiment followed up the first experiment using functional magnetic resonance imaging (fMRI) to study if and how the FPC supports shifts of visual attention in the absence of visual awareness. The third experiment, again car- ried out using fMRI, used a novel virtual foraging task to examine FPC’s implication in so-called patch-leaving behavior, that is, to what extend FPC supports partici- pants’ decision to initiate behavioral exploration. Combining signal detection theory and subjective measures of awareness in experiment 1 and 2, we showed that per- formance on unaware trials was consistent with visual selection being weighted to- wards repeated orientations of Gabor patches and reallocated in response to a novel unconsciously processed orientation. This was particularly present in trials in which the prior feature was strongly weighted and only if the novel feature was invisible. The fMRI data revealed that the ventral attention network responded to invisible feature changes whereas activity patterns in FPC conveyed the feature information of the novel stimulus attentional resources needed to be redirected to. Together these results foster the notion that FPC, not specifically implicated in the detection of in- visible stimulus changes, supports shifts of visual attention by representing infor- mation about alternative goals. Building on these findings, the third experiment showed that inter-individual differences in the propensity to pursue an either ex- ploitative or exploratory foraging strategy, indexed by participants’ giving-up times (GUT), modulated the signal strength in both medial, and lateral FPC time-locked to the onset of exploratory behavior. Those participants who showed a behavioral bias towards exploration, showed stronger signaling bilaterally in the medial and lateral FPC in the moment of exploration. Altogether, the experiments provide important new insights into FPC’s functioning that extend existing findings by showing that FPC encodes information of an unconsciously perceived stimulus attention needs to be directed to as well as that it takes a specific role in exploratory decision-making by supporting the shifting from an exploitative towards an exploratory mode of cog- nitive control. At the same time, they highlight that further research benefits from taking differences in behavioral strategies into account when making predictions about FPC’s involvement in exploratory decision-making.