Understanding brain networks underlying perceptual selection and attention in bi-stable viewing.
Final Report Abstract
In this project, we studied the neural mechanisms of perceptual selection in bi-stable viewing conditions, their interaction with top-down attention, and their relation to visual grouping and segmentation. Bi-stable visual input can perceptually be interpreted in two different, mutually exclusive ways. Such ambiguous input forces the visual system to select one of the two alternatives at a time, and perception spontaneously switches between them over the viewing period. In a series of experiments, we studied how brain areas at different levels of the visual hierarchy contribute to this perceptual selection process. We used behavioural paradigms coupled with transcranial magnetic stimulation (TMS) to probe the causal contribution of parietal and feature-selctive regions to conscious perception, and we used fMRI experiments in order to quantify neural involvement across visual and parieto-frontal regions. Our work yielded several important findings. First, we found that early visual areas such as V1 and V2 contain a fine-grained pattern of activity that reflects the subjective impression of the stimulus. When the visual stimulation was identical, but the observer experienced a coherent figure, topographic areas of the visual cortex corresponding to the figure’s foreground were ‘selected’ and their activity was enhanced, while areas corresponding to the background were suppressed. As these activity changes happen in the absence of the bottom-up input, they must be generated by a top-down feedback process. Second, we found that the mid-level visual motion-selective area V5+/MT+, contributed to the perceptual selection process in a bottom-up fashion. Interfering with its activity using transcranial magnetic brain stimulation (TMS) led to similar perceptual effects as manipulation of the physical properties of the stimulus at the input stage. This suggests that any top-down influences may happen at higher levels of the visual hierarchy. Third, we found a link between inattention symptoms in adult ADHD and the duration of perceptual transitions in bistable perception. The more severe the clinical symptoms, the longer were the transitions in our ADHD sample. These results point to the important role of inhibition at early visual processing stages in ADHD, and further studies in this direction could help understand mechanisms involved in this disorder. Fourth, a set of TMS experiments using the offline protocol of continuous theta burst stimulation (cTBS) showed that this particular TMS protocol is not a reliable method to elicit consistent behavioural effects when applied on parietal cortex, even for participants where clear effects on motor cortex were present. These results were obtained on a comparably large set of participants, replicated across several distinct bi-stable viewing paradigms, and null-findings confirmed using Bayesian analysis. Finally, a series of neuroimaging experiments provided several important insights into the role of the posterior parietal cortex (PPC) – one of the major nodes of the attention network. In several fMRI experiments we found that the region in PPC that is classically known to be involved in attention is also involved in mechanisms of rivalrous stimulus selection, stimulus grouping (i.e. reduction of items by grouping into a whole), and stimulus segmentation (i.e. segmenting items apart). We also found that PPC takes on this function regardless of stimulus size, suggesting that PPC is generally involved whenever a perceptual selection process is needed to generate a more complex interpretation of the visual input. We complemented the fMRI findings with EEG frequency analyses, and found that parietal beta-band activity correlated with internally-driven processes of Gestalt perception, providing a mechanistic link to attentional processes.
Publications
-
(2013) Perceptual effects of stimulating V5/hMT+ during binocular rivalry are state-specific. Curr Biol 23:R919–R920
Zaretskaya N, Bartels A
-
(2014) Introspection, attention or awareness? The role of the frontal lobe in binocular rivalry. Front Hum Neurosci 8
Zaretskaya N, Narinyan M
-
(2015) Gestalt perception is associated with reduced parietal beta oscillations. Neuroimage 112:61–69
Zaretskaya N, Bartels A
-
(2016) Parietal cortex mediates perceptual Gestalt grouping independent of stimulus size. Neuroimage 133:367–377
Grassi PR, Zaretskaya N, Bartels A
-
(2017) Binocular rivalry transitions predict inattention symptom severity in adult ADHD. Eur Arch Psychiatry Clin Neurosci.
Jusyte A, Zaretskaya N, Höhnle NM, Bartels A, Schönenberg M
-
(2017) Scene segmentation in early visual cortex during suppression of ventral stream regions. Neuroimage 146:71–80
Grassi PR, Zaretskaya N, Bartels A
-
(2018) A generic mechanism for perceptual organization in the parietal cortex. J Neurosci.
Grassi PR, Zaretskaya N, Bartels A
