Lead


Lay summary
It was shown that visual attention can be directed to objects. As an example, Duncan (1984) showed that participants were less accurate in reporting two features of different objects compared with two features of a single object. Findings such as Duncan's imply a coarse object representation that is generated prior to the deployment of selective attention. Early object representations are referred to as "proto-objects". The notion of proto-objects is accepted, but the exact nature of the representation and the mechanisms underlying the initial segmentation of visual input into proto-objects are not understood at present. Classical theories of perception assume that proto-objects are assembled from feature representations (color, orientation, size). Models include Treisman et al.'s (1980) Feature Integration Theory and Wolfe's (1994) Guided Search model. Feature-based accounts are supported by behavioral, psycho- and neuro-physiological evidence.The Gestalt psychologists demonstrated that human perception is sensitive to characteristics of the configuration of objects rather than to mere features. The visual system seems to segment scenes into grouped regions, proto-objects, before initiating search and recognition processes for object identification. However, Gestalt principles (e.g., proximity, similarity, closure) are descriptive rather than explanatory and post-hoc rather than predictive and open to scientific examination. In an attempt to avoid the problems of Gestalt accounts, Chen (e.g., 1982) using psychophysical methods, has emphasized the importance of topological properties for the initial visual perceptual organization. The term topology is used to describe relationships between object properties as connectivity, existence of holes or inside/outside relationships. Chen (2005) proposed that the generation of proto-objects is based on topological characteristics. The topological account constitutes a challenge to key concepts of the feature-based accounts; in particular it reverses the sequence of events of the component modules of visual information processing.The main objective of the present research project is to examine information that underlies structuring of visual scenes. Four experimental series using psychophysical methods were designed to differentiate between the two theoretical positions and to contribute to the understanding of the mechanisms underlying visual selection and the generation of an initial representation of a visual scene.