A common framework for ambylopic, developmental and adult forms of visual crowding

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In our visual field, objects are typically easy to see when we look directly at them and difficult to see in the periphery (the 'edges' of our vision). This difference is not simply to do with resolution - even when a target object in the periphery is large enough to be seen in isolation, the placement of other objects in its immediate vicinity can render the target 'jumbled' and impossible to recognise. This is known as 'visual crowding'. It is crowding and not simple resolution that limits our object recognition over more than 95% of the visual field.Although crowding does not affect the centre of gaze in 'normal' vision, it becomes elevated the case of strabismic amblyopia, often known as 'lazy eye'. Amblyopia is the most common cause of visual impairment in children and affects ~3% of the population. It is defined by impaired resolution in one eye that occurs despite optical correction. In addition, the amblyopic eye is also strongly affected by crowding - even when objects are large enough to be seen in isolation, vision at the centre of gaze is highly impaired in cluttered environments. Recent research suggests that the central vision of children younger than 12 is similarly affected by crowding. That is, where adults can recognise closely spaced objects when gazing directly at them, the same is not true for children. This places a significant restriction on the vision of children and processes such as their ability to learn to read. However, we know very little about it.We have here three instances of visual crowding: in normal peripheral vision, in amblyopic eyes and in the eyes of young children. What we do not know is whether these three forms of crowding have a common underlying cause. Can we consider each in the same way, using the same theory, and thus apply the same treatments and coping strategies to overcome crowding? Our hypothesis is that crowding in all its forms represents a form of 'compulsory integration' that occurs when the brain is faced with limited resources: when the cells in our brain that process vision are insufficient in number, they pool across extended regions to compensate. The aim of this project is to compare these three forms of crowding and determine whether they fit this common framework.The research will be conducted by psychologists, neuroscientists, orthoptists and ophthalmologists, with four specific goals. First, we will determine how crowding affects the appearance of objects. That is, do cluttered scenes look the same to children in their central vision as they do to adults in the periphery? This is central to testing the predictions of the compulsory integration theory and will lead to the development of computer models that simulate vision in these circumstances. Second, we will examine whether the peripheral field in normal vision is like the central vision of those with amblyopia - are there differences between the eyes and can we reduce them in the same way that we treat amblyopia? This creates the possibility for the 'normal' periphery to become a testing ground for new treatments of amblyopia, without the need to risk the central vision of children. Third, we will examine whether crowding is a single process in vision, or a general form of integration that affects different objects separately. For instance, does crowding affect moving objects in the same way that it affects letters? This will not only test the compulsory integration hypothesis in each instance of crowding, but also has the potential to develop new, more sensitive tests for crowding. Finally, we will scan the brains of 'normal' and amblyopic adults to measure whether the variation in crowding that occurs across the visual field follows the variation in neural resources to these same parts of the visual field. This will allow a direct test of the compulsory integration hypothesis in normal and amblyopic vision.