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Eye Movements and Perception  

Doris I. Braun and Alexander C. Schütz

Voluntary eye movements and visual perception are closely intertwined in humans and nonhuman primates because of the limitation of high-acuity vision to a very small, specialized area at the center of the retina, the fovea. Only when the image of an object is projected on the foveal region by eye and head movements it is possible, to perceive fine visual details such as letters during reading. In order to improve visual perception and to benefit from high-resolution foveal vision, rapid saccadic eye movements frequently change the direction of both eyes to selected peripheral locations. Continuous sequences of these voluntary saccades and fixations determine what humans see and in how much detail they perceive objects and their visual surroundings. Where, when, and how humans move their eyes depends not only on the visual properties of the target object but also on their intentions and prevailing tasks. Accordingly, target locations for saccades differ depending on the things people do—whether they just look around, actively search for something, read, or do sports. Instead of the classical dichotomy of bottom-up and top-down processes, recent research on gaze behavior has focused on the dynamic interplay of factors such as task demands, rewards, scene content, temporal sequences, and individual and historical differences. Besides saccadic eye movements, humans are also able to rotate their eyes continuously when they pursue moving objects of interest. Smooth pursuit eye movements stabilize the image of a moving object on the foveal region and prevent degradation of the retinal target image resulting from motion smear. The use of pursuit eye movements also improves the prediction of future target movement. Pursuit initiation is often combined with interceptive saccades that direct the fovea to the moving target, and catch-up saccades that correct for small mismatches concerning eye and target position, speed, and/or direction. Because each eye movement alters retinal input, compensations for retinal displacements are needed to maintain a stable representation of the environment. Overall, both saccadic and smooth pursuit eye movements provide optimal uptake of visual information for perception and guidance of actions.


Motor Development: Biological Aspects of Brain and Behavior  

Audrey van der Meer and F. R. (Ruud) van der Weel

Developmental psychology has a long history of linking motor development to enhancement in perceptual and cognitive abilities. Because of the haphazard appearance of the very first movements, the human infant is often thought to be born with an immature brain. However, behavioral and brain research shows that infants have advanced brains that are ready to learn even before birth. The infant brain doubles in both size and weight during the first year of life. During infancy, nerve cells increase dramatically in number, they become more specialized, and up to a thousand new connections per second are formed between them. The foundation for the brain’s infrastructure is formed during the first thousand days of life. Different neural networks are formed in response to the quantity and quality of experiences a child is exposed to. In addition, the growing brain is open and moldable, it can adapt to the changing conditions surrounding it, and the brains of infants and small children show the most plasticity. Developmental neuroscience research suggests that as soon as babies start crawling at around 9 months of age, they undergo remarkable development of prospective control and timing skills at both the brain and behavioral levels when dealing with visual motion. Only a few weeks after crawling onset, infants process visual motion faster and more efficiently, and they differentiate between motion speeds and directions. Stimulating the development of motor skills that allow babies to start exploring their surroundings by themselves earlier is therefore likely to facilitate brain development.