Seeing the unseen: Investigating and manipulating the bottom-up and top-down influences in amodal completion
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2017-08-01
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en
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Despite that most objects in the environment are partly occluded, humans perceive these as coherent complete objects. This filling-in of the missing parts, called amodal completion, seems not solely driven by bottom-up factors such as structural properties, but also by top-down factors such as knowledge about the objects. Using event-related potentials (ERPs), we replicated the findings of Hazenberg and van Lier (2016) in experiment 1 where partly occluded well-known objects were disoccluded such that the visible fragments were either connected or disconnected to each other (structure compatibility). Also, the completions could be confirming or contradicting the expectation about its well-known shape (knowledge compatibility). After disocclusion, a positive peak around 300-400 ms (P3) was observed involving both structural and knowledge influences. Additionally, we exposed a relationship between ERPs during occlusion and disocclusion. In the second experiment, we aimed to dissociate the structural bottom-up and knowledge top-down factors in amodal completion using transcranial direct current stimulation (tDCS). Our manipulation disrupted the structural influence in the peak between 100-120 ms (P1) after disocclusion while maintaining the knowledge effect. However, for occluded objects where knowledge and structure tendencies conflicted, a negative peak around 130-160 ms (N1) during occlusion was reduced compared to occlusions where knowledge and structure agreed. This finding might indicate an early role of knowledge during the microgenesis of amodal completion, conform previous literature.
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Faculteit der Sociale Wetenschappen