Representation of configural information in the visual system

Visual information that reaches the eye is complex and highly multidimensional. How is our visual system capable of extracting meaning from these inputs? In this thesis, we explored the mechanisms behind configural processing where separate parts (or features) from the inputs are organized into larger wholes. While such perceptual organization is well documented in psychology, less is known about its neural basis and possible computations leading to the structured outputs of the visual system.First, we presented participants with the so-called configural superiority task where an organization of parts into wholeshapes leads to a robust behavioral advantage in a visual search task. We found that the wholes elicited more distinct neural pattern of response than parts in higher visual areas, namely, the shape-selective lateral occipital cortex (LOC). Furthermore, by testing a neuropsychological patient DF who lacks LOC, we established a causal role of LOC in producing thisnbsp;advantage.Next, we asked what configural information in particular might be encoded in the visual system. In an fMRI experiment, we presented participants with various configurations of two lines. Some configurations were rather generic (e.g., a random placement of two lines), while others were very regular (e.g., a + sign). We found that LOC was sensitive to the amount of regularity in configurations. Moreover, in a behavioral experiment, we found that participants were also highly sensitive to changes in nonaccidental configurations that are thought to contribute to object recognition.What computations in the visual system might lead tonbsp;processing? By reviewing a large body of literature, we provide a novel synthesis of available empirical and theoretical work into a coherent framework of basic computations in the early visual processing, namely, computation of similarity between features and pooling of highly similar ones.Taken together, this thesis brings forward the idea that configural processing might be a fast and possibly feedforward process (although undoubtedly refined via recurrent loops) that is an inherent part of early visual processing.Summary Samenvatting Preface 1 | General introduction 2 | Brain-decoding fMRI reveals how wholes relate to the sum of parts 3 | Emergence of perceptual Gestalts in the human visual cortex 4 | Configural Gestalts remain nothing more than the sum of their parts in visual agnosia 5 | Encoding of configural regularity in the human visual system 6 | Sensitivity to nonaccidental configurations of two-line stimuli 7 | A conceptual framework of computations in mid-level vision 8 | General discussion Appendix A | From what scale of representation does multivariate pattern analysis decode information? Appendix B | A framework for streamlining research workflow in neuroscience and psychology Appendix C | Sharing code Acknowledgmentsnrpages: 241status: publishe