Underlying mechanisms of visual mismatch responses - An EEG-fMRI study.

Unexpected compared to expected visual events are accompanied by stronger neural responses. Two key mechanisms for these heightened responses are prediction errors to oddballs and adaptation to frequent stimuli. Whether these mechanisms vary systematically between early and late responses or differentlt in different cortical areas is yet unknown. In the current study, we simultaneously measured EEG and fMRI during an oddball task with control conditions tailored to distinguish between the different mechanisms. Results showed visual mismatch negativity and an enhanced P3 in the EEG and increased activations in the occipital cortex (OC) and superior parietal lobe (SPL) in fMRI. While adaptation predominantly drove early mismatch responses in the EEG and posterior OC, responses at later time points and in the anterior OC and SPL could best be explained by prediction error. This pattern suggests that the relative contribution of different mechanisms to deviance processing varies systematically in time and space.