The influence of aperture surfaces on the barber-pole illusion

The magnitude of the barber-pole illusion is measured as a function of the contrast, orientation, and phase difference between the moving 'barber-pole' grating and a moving 'surround' grating that forms the aperture surface. It is found that as the difference between the barber-pole gratind and the surround grating increases, the influence of surround motion on barber-pole motion decreases (resulting in an increase in the magnitude of the barber-pole illusion). This pattern of results is interpreted as evidence for competition between processes that detect the motion of line terminators along the length of the rectangular aperture and processes that detect grating motion in directions perpendicular to grating orientation.