Competition Between The Brightness Contrast And Topological Structure In Visual Perception

Almost all the object's features such as shape, size, brightness, color, even topological structure are related to perceptual organization. And each of them has a unique role in perceptual process. The present study mainly focused on the role of topological structure and brightness contrast in perceptual organization and perceptual selection. The theory of topological perception in visual perception led a new study direction, and we always considered it as one of the most important and classic psychological findings. The theory of topological perception argued that a primitive and general function of the visual system was the perception of global topological properties. It emphasizes that the nature of perceptual organization should be understand from the perspective of transformations and invariants over shape-changing transformations. However, when we tried to explain our previous study by virtue of the theory of topological perception, we found that the differences in topological structure between a connected component with a hole and one with no hole are not substantive which might be confounded by another counter explanation which did never be recognized before, such as the simultaneous brightness contrast. For this reason, in the current study we sought to explore the relationship of topological structure and brightness contrast in visual perceptual grouping and selective attention from the behavioral and neurophysiological perspectives.In the first part of this study, the purpose is to explore the psychological processes that underlie the conflict perceptual grouping by similarity in shape, brightness contrast and topological structure of 2-D geometric figures in three experiments. In experiment 1, the effect of brightness contrast on perceiving shape and topological structures was examined. In experiment 2, observers' sensitivity between the brightness contrast, shape and topological structure in grouping was further tested. In experiment 3, the effect of pattern complexity on the perception of shape and topological structures was examined for line drawings.The main findings are as follows: (1) The brightness contrast is significantly easier and quicker to be detected than the topological structure. (2) The brightness contrast has no effect on shape perception, but the complexity of the pattern does, the more lines it has, the easier it can be captured. (3) The brightness contrast facilitated the detection of topological structure, while the complexity of the pattern has an opposite effect. The topological structure is more difficult to be detected with the increasing of complexity when the brightness contrast was controlled to the minimum.In the second part of this study, event-related potentials (ERPs) were recorded when the subjects attended selectively to a specified attributes (brightness or topological structure) and responded to the targets including designated feature value. The results showed that selection to brightness or topological structure elicited frontal selection positivity (FSP), selection negativity (SN), N2b, P3b, and a late negative component (LNC). The onset latency of SN which reflected non-spatial attributes attention effects was earlier for brightness selection than for topological structure selection. Moreover, in the brightness selection task, there was no difference in the ERPs between two target stimuli or between two non-target stimuli. But in the topological structure task, the ERPs were significantly different between two target stimuli, as well as two non-target stimuli. In the mean time, these ERPs data were also consistent with the results in reaction times.From these results of the current study, we can conclude that the topological distinction between two luminance-defined stimuli is intrinsically related to the brightness contrast. The processing of brightness occurs earlier than the processing of topological structure. Furthermore, selection by brightness inhibits topology processing, while selection by topological structure doesn't inhibit brightness processing. Therefore, we suggest that global topological properties can be alternatively explained by brightness contrast, or more radically, brightness contrast played more important role than topological structure in perceptual grouping and in the selective attention.