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Radboud University, 18 september 2023, Promotores : Fries, P., Poeppel, D., Contains fulltext : 295471.pdf (Publisher’s version ) (Closed access), Visual gamma oscillations are a network phenomenon generated by excitation-inhibition interactions in early visual cortex. They depend on stimulus drive and homogeneity, can be influenced by cognitive and stimulus-history factors, and have been proposed to underlie both the binding of visual information into objects, and selective neuronal communication. While tremendous progress has been achieved over the last thirty years, many questions on the mechanisms, prerequisites, and functions of gamma oscillations remain. Using MEG and psychophysical experiments in human participants, I have demonstrated that a) colored stimuli of equal L-M retinal cone contrast induce equally strong gamma oscillations, that b) gamma oscillations show gamma repetition suppression over few stimulus repetitions and gamma repetition enhancement over many repetitions, that gamma repetition enhancements are stimulus-specific, persist over many minutes and strengthen feedforward functional connectivity along the visual hierarchy, and that c) as predicted by the CTC hypothesis of gamma function, phase-leading stimuli are processed and perceived more intensely than phase-lagging stimuli.

20 januari 2021, Item does not contain fulltext

Radboud University, 07 juli 2022, Promotores : Poeppel, D., Norris, D.G. Co-promotor : Michalareas, G., Contains fulltext : 251083.pdf (Publisher’s version ) (Open Access)

Planning to speak is a challenge for the brain, and the challenge varies between and within languages. Yet, little is known about how neural processes react to these variable challenges beyond the planning of individual words. Here, we examine how fundamental differences in syntax shape the time course of sentence planning. Most languages treat alike (i.e., align with each other) the 2 uses of a word like “gardener” in “the gardener crouched” and in “the gardener planted trees.” A minority keeps these formally distinct by adding special marking in 1 case, and some languages display both aligned and nonaligned expressions. Exploiting such a contrast in Hindi, we used electroencephalography (EEG) and eye tracking to suggest that this difference is associated with distinct patterns of neural processing and gaze behavior during early planning stages, preceding phonological word form preparation. Planning sentences with aligned expressions induces larger synchronization in the theta frequency band, suggesting higher working memory engagement, and more visual attention to agents than planning nonaligned sentences, suggesting delayed commitment to the relational details of the event. Furthermore, plain, unmarked expressions are associated with larger desynchronization in the alpha band than expressions with special markers, suggesting more engagement in information processing to keep overlapping structures distinct during planning. Our findings contrast with the observation that the form of aligned expressions is simpler, and they suggest that the global preference for alignment is driven not by its neurophysiological effect on sentence planning but by other sources, possibly by aspects of production flexibility and fluency or by sentence comprehension. This challenges current theories on how production and comprehension may affect the evolution and distribution of syntactic variants in the world’s languages.