Understanding brain networks underlying perceptual selection and attention in bi-stable viewing.

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Perceptual selection is a fundamental function of our brain. When confronted with complex or ambiguous visual input, our brain selects and consciously perceives the relevant information and suppresses the irrelevant, automatically and without mental effort. In contrast to this, directing visual attention towards particular locations or features is an effortful and active process that can directly support or interact with automatic selection processes, by enhancing neural representations of the attended stimuli. At the neural level, only little is understood about the relationship between the seemingly spontaneous and automatic nature of perceptual selection, the role of attention in it, and their contribution to gating access to consciousness. In the current application, our main interest lies in examining neural processes involved in bistable selection and their interaction with mechanisms of directed attention. We aim to shed light on the influence of neural populations encoding consciously perceived versus unperceived stimuli on the outcome of perceptual selection, and aim to measure their respective modulation by directed attention. To achieve this, we will examine different nodes of the fronto-parietal attention network and their interaction with mid-level and early visual cortices. Psychophysics suggest that bi-stable viewing involves strong interactions between early and higher levels of processing, yet only little is known about the neural substrates underlying this communication, and whether it differs during automatic perceptual selection and during directed attention. It is also unknown how it affects neural populations encoding the perceived versus non-perceived stimulus representations. These questions may shed additional light onto potential reasons underlying the discrepancy between electrophysiological and neuroimaging signals observed in bi-stable vision experiments in early visual cortex.We propose five sets of experiments conducted by two researchers, addressing each of the above questions using the appropriate method. In particular, we will disturb brain activity using transcranial magnetic stimulation (TMS) in prefrontal, parietal and visually specialized areas with and without conscious access to probe their direct influence on perceptual selection. fMRI experiments at 3 Tesla will complement these studies at the whole-brain level. Ultra-high-resolution fMRI studies using 9.4 Tesla aim to resolve activity of different cortical layers to examine feedforward and feedback influences on neural populations with or without conscious access, with and without top-down attention.The results will provide unprecedented insights into neural mechanisms of perceptual selection and their relation to visual attention, and shed a fundamental light onto the relationship of both to conscious and unconscious processing.