The extrafoveal preview paradigm as a measure of predictive, active sampling in visual perception.

A key feature of visual processing in humans is the use of saccadic eye movements to look around the environment. Saccades are typically used to bring relevant information, which is glimpsed with extrafoveal vision, into the high-resolution fovea for further processing. With the exception of some unusual circumstances, such as the first fixation when walking into a room, our saccades are mainly guided based on this extrafoveal preview. In contrast, the majority of experimental studies in vision science have investigated "passive" behavioral and neural responses to suddenly appearing and often temporally or spatially unpredictable stimuli. As reviewed here, a growing number of studies have investigated visual processing of objects under more natural viewing conditions in which observers move their eyes to a stationary stimulus, visible previously in extrafoveal vision, during each trial. These studies demonstrate that the extrafoveal preview has a profound influence on visual processing of objects, both for behavior and neural activity. Starting from the preview effect in reading research we follow subsequent developments in vision research more generally and finally argue that taking such evidence seriously leads to a reconceptualization of the nature of human visual perception that incorporates the strong influence of prediction and action on sensory processing. We review theoretical perspectives on visual perception under naturalistic viewing conditions, including theories of active vision, active sensing, and sampling. Although the extrafoveal preview paradigm has already provided useful information about the timing of, and potential mechanisms for, the close interaction of the oculomotor and visual systems while reading and in natural scenes, the findings thus far also raise many new questions for future research.