We studied the influence of knowledge in the interpretation of partly occluded objects. In the past decades, amodal completion has often been studied by using abstract, meaningless outlines of rather stylistic, geometric shapes. It has been recognized that smooth continuation of partly occluded contours behind an occluding surface is a strong completion tendency. In the current study we contrast this structurally driven completion tendency with knowledge driven tendencies. We used a set of partly occluded well-known objects for which structure-based completions and knowledge-based completions resulted in either the same or different interpretations. We adopted the behavioural primed matching paradigm to measure differential priming effects due to these completion tendencies. Our results implied differential temporal properties for structure-based and knowledge-based effects during perception of partly occluded objects. Interestingly, knowledge has an influence as early as 150 ms after the onset of the prime.

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The aim of this study was to investigate the temporal cortical activation patterns underlying different stages of humor comprehension (e.g., detection of incongruity stage, resolution of incongruity stage, and affective stage). Event-related potentials (ERPs) were measured when 16 subjects were apprehending cartoon pictures including humorous, non-humorous and unrelated items. Results showed that both humorous and unrelated items elicited a more negative ERP deflection (N500-800) than non-humorous ones between 500-800 ms, which might reflect detection to incongruent element during humor apprehension. Then, both humorous and non-humorous items elicited a more positive ERP deflection (P800-1000) than unrelated ones between 800-1000 ms, which might reflect a classification process preliminarily evaluating whether there were attainable cues in the pictures used to form possible association between context and picture (we named it "association evaluation" stage). Furthermore, humorous items elicited a more positive slow wave than non-humorous items which also elicited a more positive wave than unrelated items between 1000-1600 ms, during which this component might be involved in the forming of novel associations (resolution of incongruity). Lastly, between 1600-2000 ms, humorous items elicited a more positive ERP deflection (P1600-2000) than both non-humorous and unrelated items, which might be related to emotion processing during humor apprehension. Based on these results, we deeply subdivided the second stage (resolution of incongruity) into two stages: association evaluation and incongruity resolution.

We studied interpretations of partly occluded shapes. Models that account for amodal completion mostly deal with local and global contour characteristics. In the current study, we were interested in the effects of colour on local and global contour completions. In our stimuli, local contour completions comprised simple linear extensions of the partly occluded contours, whereas global contour completions accounted for global shape regularities. Our stimuli were designed such that the visible surface colour could also be completed in a local or global fashion, being consistent or inconsistent with contour completions. We tested the preferred interpretations of the partly occluded shapes by using a sequential matching task. Participants had to judge whether a test shape could be a previously shown partly occluded shape. We found that interpretations of partly occluded shapes depend on both colour and contour characteristics. Additional time bin analyses revealed that for fast responses colour and contour completions already depend on the visible context of the partly occluded shapes, while for slow responses the congruency between colour and contour completions play a role as well.

We studied neural correlates accompanying the Fraser spiral illusion. The Fraser spiral illusion consists of twisted cords superimposed on a patchwork background arranged in concentric circles, which is typically perceived as a spiral. We tested four displays: the Fraser spiral illusion and three variants derived from it by orthogonally combining featural properties. In our stimuli, the shape of the cords comprised either concentric circles or a single spiral. The cords themselves consisted of black and white lines in parallel to the contour of the cords (i.e., parallel cords), or oblique line elements (i.e., twisted cords). The displays with twisted cords successfully induced illusory percepts, i.e., circles looked like spirals (the Fraser spiral illusion) and spirals looked like circles (i.e., a “reverse Fraser illusion”). We compared the event-related potentials in a Stimulus (Circle, Spiral) × Percept (Circle, Spiral) design. A significant main effect of Stimulus was found at the posterior scalp in an early component (P220-280) and a significant main effect of Percept was found over the anterior scalp in a later component (P350-450). Although the EEG data suggest stimulus-based processing in the posterior area in an early time window and percept-based processing in the later time window, an overall clear-cut stimulus-percept segregation was not found due to additional interaction effects. Instead, the data, especially in the later time window in the anterior area, point at differential processing for the condition comprising circle shapes but spiral percepts (i.e., the Fraser illusion).