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Abstracts
  • Kornmeier, J., & Bach, M. (2006). Bistable perception -- along the processing chain from ambiguous visual input to a stable percept. International Journal of Psychophysiology : Official Journal of the International Organization of Psychophysiology, 62(2), 345–349. https://doi.org/10.1016/j.ijpsycho.2006.04.007

    The observation of an ambiguous figure leads to spontaneous perceptual reversals while the observed picture stays unchanged. Some ERP studies on ambiguous figures report a P300-like component correlated with perceptual reversals supporting a top-down explanation, while other studies found early visual ERP components supporting a bottom-up explanation. Based on an experimental paradigm that permits a high temporal resolution of the endogenous reversal event, we compared endogenous Necker-cube reversals with exogenously-induced reversals of unambiguous cube variants. For both reversal types, we found a chain of ERP components with the following characteristics: (1) An early occipital ERP component (130 ms) is restricted to endogenous reversals. (2) All subsequent components also appear with exogenously-induced reversals, however 40-90 ms earlier than their endogenous counterparts. (3) The latency difference between reversal types is also reflected in the timing of manual reactions, which occur 100-130 ms after P300-like components. The results suggest that the P300-like component is the same as found in other ERP studies on ambiguous figures. This component does not reflect the reversal per se, but rather its cognitive analysis, 300 ms after a change of the representation in early visual areas. The presented ERP chains integrate the different ERP results and allow to pinpoint the steps where top-down mechanisms begin to exert their influence.

  • Kornmeier, J., Pfäffle, M., & Bach, M. (2011). Necker cube: stimulus-related (low-level) and percept-related (high-level) EEG signatures early in occipital cortex. Journal of Vision, 11(9), 12. https://doi.org/10.1167/11.9.12

    During observation of an ambiguous Necker cube, our percept changes spontaneously although the external stimulus does not. An EEG paradigm allowing time-resolved EEG measurement during endogenous perceptual reversals recently revealed a chain of ERP correlates beginning with an early occipital positivity at around 130 ms (Reversal Positivity, "RP"). In order to better understand the functional role of this RP, we investigated its relation to the P100, which is spatiotemporally close, typically occurring 100 ms after onset of a visual stimulus at occipital electrodes. We compared the relation of the ERP amplitudes to varying sizes of ambiguous Necker cubes. The main results are: (1) The P100 amplitude increases monotonically with stimulus size but is independent of the participants' percept. (2) The RP, in contrast, is percept-related and largely unaffected by stimulus size. (3) A similar pattern to RP was found for reaction times: They depend on the percept but not on stimulus size. We speculate that the P100 reflects processing of elementary visual features, while the RP is related to a processing conflict during 3D interpretation that precedes a reversal. The present results indicate that low-level visual processing (related to stimulus size) and (relative) high-level processing (related to perceptual reversal) occur in close spatial and temporal vicinity.

  • Kornmeier, J., Ehm, W., Bigalke, H., & Bach, M. (2007). Discontinuous presentation of ambiguous figures: how interstimulus-interval durations affect reversal dynamics and ERPs. Psychophysiology, 44(4), 552–560. https://doi.org/10.1111/j.1469-8986.2007.00525.x

    If we observe an ambiguous figure, our percept is unstable and alternates between the possible interpretations. Periodically interrupting the presentation sizably modulates the spontaneous reversal rate. We here studied event-related potential (ERP) correlates of the neural processes underlying these strong modulations. An ambiguous Necker stimulus was presented discontinuously with four randomly varying interstimulus intervals (ISI; 14, 43, 130, 390 ms) while participants indicated perceptual reversals. EEG was selectively averaged with respect to the participants' percept and ISI. ERP traces varied markedly between ISIs. A simple model explained a major part of this variation and showed that the ISI-dependent ERP modulation occurs after disambiguation has already taken place. We suggest that perceptual stability (or reversal) depends on a system state, slowly changing from one reversal to the next. ISI can shift this state on a scale between stability and instability.

  • Kornmeier, J., Wörner, R., Riedel, A., Bach, M., & Tebartz van Elst, L. (2014). A different view on the checkerboard? Alterations in early and late visually evoked EEG potentials in Asperger observers. PloS One, 9(3), e90993. https://doi.org/10.1371/journal.pone.0090993

    BACKGROUND: Asperger Autism is a lifelong psychiatric condition with highly circumscribed interests and routines, problems in social cognition, verbal and nonverbal communication, and also perceptual abnormalities with sensory hypersensitivity. To objectify both lower-level visual and cognitive alterations we looked for differences in visual event-related potentials (EEG) between Asperger observers and matched controls while they observed simple checkerboard stimuli. METHODS: In a balanced oddball paradigm checkerboards of two checksizes (0.6° and 1.2°) were presented with different frequencies. Participants counted the occurrence times of the rare fine or rare coarse checkerboards in different experimental conditions. We focused on early visual ERP differences as a function of checkerboard size and the classical P3b ERP component as an indicator of cognitive processing. RESULTS: We found an early (100-200 ms after stimulus onset) occipital ERP effect of checkerboard size (dominant spatial frequency). This effect was weaker in the Asperger than in the control observers. Further a typical parietal/central oddball-P3b occurred at 500 ms with the rare checkerboards. The P3b showed a right-hemispheric lateralization, which was more prominent in Asperger than in control observers. DISCUSSION: The difference in the early occipital ERP effect between the two groups may be a physiological marker of differences in the processing of small visual details in Asperger observers compared to normal controls. The stronger lateralization of the P3b in Asperger observers may indicate a stronger involvement of the right-hemispheric network of bottom-up attention. The lateralization of the P3b signal might be a compensatory consequence of the compromised early checksize effect. Higher-level analytical information processing units may need to compensate for difficulties in low-level signal analysis.

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