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Jonathan Wynn, Amy Jimenez, William Horan, Junghee Lee, Gabrielle Pascual, Eric Reavis, Michael Green; Illusory and Real Contour Processing: Findings from a Joint Event-related Potential – Functional MRI Analysis. Journal of Vision 2016;16(12):135. doi: 10.1167/16.12.135.
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Neural mechanisms involved in processing real and illusory contours (e.g., Kanizsa figures) have previously been assessed with event-related potentials (ERPs) or functional MRI (fMRI). In our study, we combined information from EEG and fMRI to assess the underlying neural structures and chronometry associated with illusory and real contour processing. ERP and fMRI data were collected from 20 participants who viewed images containing illusory contours (IC), no contours (NC), or real contours (RC). The P100, N100 and P200 ERP responses to the images were analyzed in the EEG data. The N100 was significantly larger for IC vs. NC, while the P200 was significantly larger for RC vs. IC. In the MRI data, the main contrasts examined were IC vs. NC and IC vs. RC. All stimuli activated the lateral occipital complex (LOC), with no significant differences in activation. We combined information from both modalities using a joint independent component analysis (jICA) approach (Calhoun et al., 2006), comparing IC vs. NC stimuli, and IC vs. RC stimuli. For jICA, the N100 was associated with activity in a frontal-parietal network, including the middle frontal gyrus, superior parietal lobule, and LOC, with significantly more activity for IC vs. RC and NC stimuli. The P200 was linked to activity in the occipital cortex, primarily LOC, and was significantly larger for RC vs. IC and NC stimuli. The ICA-based joint spatiotemporal analysis revealed findings that were not discernible in either the ERP and fMRI results alone. The analysis suggests that illusory contour processing involves both frontal and parietal regions to a greater extent than real contour processing. By contrast, the analysis suggests that processing of real contours is more closely associated with occipital activity. These results are consistent with a "frame-and-fill" mechanism.
Meeting abstract presented at VSS 2016
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