| Popis: |
During the observation of an ambiguous figure, our perception becomes unstable and alternates repeatedly between mutual exclusive interpretations. Tiny changes of the stimulus features can disambiguate the figure and stabilize percepts. Recent EEG studies found much smaller amplitudes of two event-related potentials (ERPs), an anterior P200, 200 ms after stimulus onset and a posterior P400, 200 ms later, when participants observed an ambiguous stimulus compared to disambiguated stimulus variants. Interestingly, this pattern of results was found across stimuli differing in ambiguity (geometry, motion and gestalt) and in visibility. We postulate a meta-perceptual / meta-cognitive evaluation instance that rates the reliability of perceptual constructs at a high processing level generalized beyond sensory details. We further postulate that the above described ERP effects reflect the outcome of this evaluation process. According to these hypotheses, the distributions of these ERP effects on the scalp across three different stimulus categories, should originate from the same neural structures in the sensor and source space. This was tested by calculating EEG inverse solutions using a novel artificial neural network-based approach.We found very similar sources across stimulus categories, both on the level of individual participants and on the group level. Regions involved in the earlier processing steps (P200) encompass lateral occipital cortex, inferior parietal cortex and medial cingulate cortex. Later processes (P400) originated mostly from the right inferior temporal cortex. Our findings were consistent with comparable studies using functional magnetic resonance imaging and EEG source imaging. In summary, we found highly coherent neural sources of the ERP Uncertainty Effects. The underlying processes may be related to a common uncertainty resolution at a higher processing level beyond sensory details. |
