Adaptation to incomplete flow patterns: no evidence for 'filling-in' the perception of flow patterns.

Inspecting a radial flow pattern reduced visual sensitivity to changes in the size of a test square of 0.5 deg side length when the square was accurately located at the point previously occupied by the focus of the adapting flow pattern. The effect was reduced by a third when there was a 1.0 deg diameter hole at the centre of the flow pattern, and abolished when the hole was 1.5 or 2.0 deg in diameter. These findings support the idea that any depression of sensitivity in the hole is entirely due to spread of adaptation from the stimulated region, and provide no evidence for 'filling-in' or 'visual-phantom' phenomena in flow patterns.