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TY - THES AU - Kiefer, Christian Matthias TI - Visual processing of naturalistic images: free viewing, guided visual searching, and memorization PB - RWTH Aachen University VL - Dissertation CY - Aachen M1 - RWTH-2023-08679 SP - 1 Online-Ressource : Illustrationen, Diagramme PY - 2023 N1 - Veröffentlicht auf dem Publikationsserver der RWTH Aachen University N1 - Dissertation, RWTH Aachen University, 2023 AB - Under natural conditions, eye movements are used to actively gather visual information from the environment, a process referred to as ‘active vision’. Despite active vision forming the basis for visual exploration in everyday life, research has often focused on simplified, artificial scenarios with restricted eye movements. As a result, the mechanisms underlying active vision remain comparatively unexplored. Particularly, it is unclear how goal-directed behavior such as during the search for a particular object influences the visual processing during active vision. In this dissertation, three distinct modes of active vision were investigated in a study of 31 subjects: performing a guided visual search and memorizing objects were compared to the free viewing of naturalistic images. Magnetoencephalography was used in conjunction with an eye-tracking system to simultaneously record the brain activity and the eye movements during the tasks while the subjects were viewing naturalistic images with embedded objects. To answer the question of how visual processing is affected by goal-directed behavior, causal interactions in the brain were compared for the free viewing and the visual searching tasks. First, regions of interest exhibiting significant fixation-related evoked activity were determined using spatiotemporal cluster permutation testing. Then, using generalized partial directed coherence, the whole-brain causality networks between these regions were computed. Four regions, namely the supramarginal gyrus, the superior temporal gyrus, the transverse temporal gyri, and the posterior insula, formed during free viewing a cluster in both hemispheres that was highly inter-connected. A near-identical cluster emerged during searching in the right hemisphere with the right supramarginal gyrus as a central node in the network. Based on the results, all four regions are likely involved in guiding attention and visual processing. Specifically, the right supramarginal gyrus might be involved in the integration of visual input related to objects. Furthermore, it might provide the supplementary eye field with information for the purpose of updating the search priority map, which guides the eye movements towards the search target. Finally, the random convolutional kernel transformation (ROCKET) classifier for time series was applied to the fixation-related evoked activity of object fixations performed during the memorization and the free viewing tasks. It was possible to classify unseen fixation data based on the task with 93 LB - PUB:(DE-HGF)11 DO - DOI:10.18154/RWTH-2023-08679 UR - https://publications.rwth-aachen.de/record/968610 ER -