Spatial numbers: How visual crowding and redundancy masking modulate numerosity perception

The increasing visual complexity of our environment requires humans to process information in efficient ways. For example, digital displays are often cluttered with items, making tasks difficult, and overwhelming the attentional system. Here, we will investigate visual information processing in cluttered scenes. By combining basic spatial vision research and research in numerical cognition, we will shed light on the underlying mechanisms of numerosity perception (i.e. determining the number of a visual set of objects), and the integration mechanisms of the visual brain. In particular, we will investigate how the ability to estimate the number of items present in a visual scene is determined by visual crowding. Visual crowding is the phenomenon that a target stimulus that is easily identified when presented alone becomes difficult to identify when presented flanked by other items. In cluttered environments, crowding is the strongest limiting factor of visual perception, fundamentally constraining our ability to navigate, to read, and to interact with digital interfaces. Although recent studies addressed the link between crowding and numerosity, it is so far unknown in how far crowding underlies the perception of numerosity. Here, we will make use of a number of fundamental characteristics of crowding, for example, its asymmetry and individual differences to shed light on the role of crowding in numerosity perception. The results of three series of psychophysical experiments will advance our understanding of crowding and numerosity perception, and enable us to derive recommendations for the design of perceptually improved applications and environments.