Neural processing of sensory ambiguity in healthy subjects and patients with Asperger Autism

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The perception of an ambiguous figure is unstable and alternates between possible interpreta-tions. Tiny figural changes can disambiguate an ambiguous stimulus and stabilize its percept. Recently, we found two prominent event-related potentials, a fronto-central P200 and a pari-eto-central P400 with the following features: (1) their amplitudes increase monotonically with decreasing stimulus ambiguity and (2) their timing and spatial distributions are highly similar across very different visual dimensions (geometry, semantics and motion). We interpret these components in the context of the following model: Our perceptual system matches the incomplete and ambiguous sensory input with perceptual memory contents in order to construct stable and reliable percepts. A high-level probabilistic (Bayesian) inference unit calculates the reliability of the perceptual constructs, the result being reflected in the P200 and P400 amplitudes. The objective of this proposal has two tracks: In the Basic Research track we aim to study: (1) the generalisation of the P200/P400 ambi-guity effects across sensory modalities (visual, auditory, somatosensory), (2) the functional difference between P200 and P400, and (3) their spatial sources. The results from this track will help to further our understanding of the neural processes underlying perceptual reliability at an advanced cognitive level, integrated across sensory modalities.In the Clinical Research track we focus on participants with Asperger Autism (AA). AA par-ticipants rely more on sensory information and less on perceptual memory. Based on our model we predict that their P200/P400 amplitudes differ from controls, with steeper increases and lower maxima. We aim to study differences between AA participants and matched con-trols using: (1) a new behavioural marker (hysteresis distance) to quantify the influence of the preceding perceptual history on the current percept, (2) the relation between the hysteresis distance and the P200/P400 effect size and, (3) P200/P400 amplitude patterns with hidden figures, whose percepts depend mainly on the availability of perceptual memory contents. Although the perceptual symptoms of AA have recently gained importance in diagnostics, their underlying mechanisms are still poorly understood. The results form this track will help to clarify the specific feature of perceptual disambiguation in AA participants. Also, physio-logical markers of AA have been rare so far. The large effect sizes of the P200/P400 effects allow statistics within single participants and are thus promising candidates for such a marker.