Feature mixing rather than feature replacement during perceptual filling-in

‘Filling-in’ occurs when a retinally stabilized object subjectively appears to vanish following perceptual fading of its boundaries. The term ‘filling-in’ literally means that information about the apparently vanished object is lost and replaced solely by information arising from the surrounding background. However, we find evidence that the mechanism of ‘filling-in’ can actually involve a process of ‘feature mixing’ rather than ‘feature replacement,’ whereby features on either side of a perceptually faded boundary merge. Here we investigate the properties of feature mixing and specify certain conditions under which such mixing occurs. Our results show that, when using visual stimuli composed of spatially alternating stripes containing different luminances or motion signals, and when using the neon-color-spreading paradigm, the filled-in luminance, motion, or color is approximately the area and magnitude weighted average of the background and the foreground luminance, motion, or color, respectively. Together, these results demonstrate that, under at least certain conditions, ‘filling-in’ may involve a process of feature mixing or feature averaging rather than one of feature replacement.