The information available via our senses is restricted and to varying degrees ambiguous. It needs to be disambiguated and continuously
interpreted in order to construct stable and reliable percepts. The discrimination between reality and illusion is thus to a large degree based on
the capability of our perceptual system. Ambiguous figures are paradigmatic examples in this context. The observed stimulus, e.g. a Necker
cube, is maximally ambiguous, and percepts become unstable and alternate repeatedly between possible outcomes although the underlying
stimulus stays unchanged. We use this phenomenon of perceptual instability to study the psycho-physical relations and altered states of consciousness.
How long lasts a moment? The answer to this question is important for the understanding of perceptual processes, of consciousness and
also of altered states of consciousness. The estimated duration of a moment - about 3 s - corresponds to the duration of a temporal
Gestalt in music, to the duration of a linguistic element and also to the average duration of perceptual stability ("dwell time") of
an ambiguous figure. In the xx Achtsamkeitsmeditation meditators focus on the present moment in order to achieve an altered state of
consciousness with increased attention and high emotional control. It is assumed that the duration of a moment will be extended in such
an altered state of consciousness. Confirmation comes from experienced meditators. They show longer ambiguous figure dwell times
compared to non-meditating
The recently presented Necker-Zeno-model of bistable perception presents a mathematical relation between dwell times and two other basic
time scales of cognitive relevance: (a)the order threshold, (i.e. the minimal temporal distance of about 30 ms between two successive
stimuli to identify their order) and (b) the duration of about 300 ms between stimulus onset and perceptual awareness of the stimulus.
This model predicts that the temporal extension of a moment correlates with a deceleration of perceptual awareness and/or a shortening of the
order threshold (Atmanspacher et al. 2008). In an EEG study on the perception of ambiguous figures with meditators and non-meditator controls
we test these model predictions by focusing on the temporal patterns of event related potentials that are specific to the perception of
ambiguous figures (Kornmeier & Bach 2012).
Perception of ambiguous figures is unstable and alternates between different interpretations. Tiny figural changes can disambiguate an
ambiguous stimulus and stabilize its percept. Recently, we found an ERP ambiguity effect, consisting of two event-related potentials, a
fronto-central P200 and a parieto-central P400, with the following features: (a) the ERP amplitudes increase monotonously with decreasing
stimulus ambiguity, (b) the ERP latencies and spatial distributions are very similar across highly different visual categories (geometry,
motion and semantics, see Figure below).
We interpret these effects in the context of the following model: Our perceptual system weights the sensory information with concepts from
perceptual memory in order to construct stable and reliable percepts. A probabilistic inference unit estimates the reliability of the perceptual
constructs and the P200 and P400 amplitudes reflect the result. In a series of current projects we test the generalization of the ERP ambiguity
effect across modalities (visual, auditory and tactile). Further we plan to compare brain sources of the P200 and P400 signatures between
Perceptions result from a weighting of exogenous sensory information with endogenous memory concepts (see above). This weighting can
be biased in either direction, depending on the quality of the sensory information. Patients with Asperger Autism Spectrum Disorder put
more weight on sensory information and less weight on endogenous memorized concepts. In a cooperation project with the Clinic for
Psychiatry and Psychotherapy of the University Freiburg we study whether such perceptual differences between patients and healthy controls
are reflected in an altered ERP ambiguity effect (see above). We further plan a project where we compare the ERP ambiguity effect in
patients with Schizophrenia Spectrum Disorder and healthy controls.
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PD Dr. H. Atmanspacher (IGPP, Freiburg & Collegium Helveticum, Zürich, Schweiz)
Prof. M. Bach (Universitäts-Augenklinik, Freiburg)
Prof. M. Castelo-Branco (University of Coimbra, Portugal) /
PD Dr. T. Filk (Physik, Universität Freiburg)
Prof. G. Folkers (Collegium Helveticum, Zürich, Schweiz)
Dr. A. Giersch (Psychiatrie der Universität Strasbourg)
PD Dr. SP. Heinrich (Universitäts-Augenklinik, Freiburg)
Prof. R. O'Shea (Southern Cross University, Coffs Harbour, Australien)
Dr. Z. Sosic-Vasic (Psychiatrie der Universität Ulm)
Prof. M. Spitzer (Psychiatrie der Universität Ulm)
Prof. T. Stieglitz (Technische Fakultät der Universität Freiburg)
PD Dr. R. Roeber (Institut für Psychologie, Universität Leipzig)
Prof. L. Tebartz van Elst (Psychiatrie der Universität Freiburg)
PD Dr M. Wittmann (IGPP)