Visual processing of contours and textures

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This application is for funds to continue my studies into the visual processing of contours and textures. The visual ability to detect the shapes of contours, such as the outline of a pear, and the structure of textures, such as the pattern on a carpet or the bark of a tree, is essential for recognizing patterns, objects and the shapes of textured surfaces. My experiments use behavioural or ‘psychophysical’ methods with normal human test subjects. In a typical experiment, subjects view large numbers of specially-designed computer-generated test patterns presented on a display monitor and are required to make for each a forced-choice judgement; for example which of two shapes is the one previously shown, which of two patterns is the more regularly arranged, which of two textures contains a circular structure. One of my experimental methods also exploits a phenomenon termed the ‘visual after-effect’. Prolonged viewing, termed ‘adaptation’, of a particular contour shape or texture causes subsequently presented contours/textures to appear distorted. By measuring the amount of distortion, much can be learnt about how the brain processes contour and texture information. For example, a fundamental feature of texture patterns is regularity, or ‘repeatedness’, for example as in the repeating pattern of a carpet. If one takes a highly regular texture pattern, such as an array of dots arranged perfectly on a grid, and adapts to it, a slightly less regular pattern appears even less regular than otherwise. This effect is termed the ‘regularity after-effect’, and the fact that it happens at all suggests that there are neurons in the brain that are specialized for seeing regularity. By measuring the regularity aftereffect for various types of texture pattern and constructing computer models of how the neurons might encode regularity, one can work out how the brain detects and encodes regularity in a texture pattern. Together with my other experiments on shape coding and texture, my research will therefore lead to a better understanding of how the brain sees the shapes of contours and the structure of textures.