The effects of stimulus contrast, background intensity, and stimulus duration on switch visual afterimages

The objective of this study was to systematically evaluate the properties of a new kind of visual afterimage. In a switch visual afterimage, the colors of the inducing image switch locations in the afterimage. For example, a black and blue square-wave grating stimulus produces a blue and black square-wave grating afterimage. Three observers participated in seven experiments, in which they were asked to report on either the color of the inducing stimulus (a physically presented image) or a perceived afterimage. Observers used a color selector where they matched an on-screen color to the memory of the color of a percept (inducing stimulus or afterimage) they had just experienced. One of the critical factors in understanding the switch afterimage was found to be the spatial contrast of the inducing image. Experiments 3, 5, and 7 explored the effects of stimulus contrast on the switch visual afterimage. In Experiment 3, the inducing stimulus was a 1, 2, 3, 4, 5, 6, 7, or 18 bar black and blue or blue and black square-wave grating. When the inducing stimulus was a single bar observers reported seeing a negative afterimage, but as the number of bars in the inducing stimulus was increased observers increasingly reported seeing a switch afterimage. Experiment 5 showed that this effect did not generalize to blue and white bar gratings. Observers reported seeing a negative afterimage after viewing a blue and white or white and blue square-wave grating. Experiment 7 showed that a blue bar flanked by black and white bars produces a mix of a negative and a switch afterimage. Changing the intensity of the viewing background (Experiment 4) and the viewing duration of the inducing image (Experiment 6) did not strongly influence the type of afterimage reported by observers (negative or switch), but did influence the lightness and chroma of observer’s afterimages. Increases in the intensity of the viewing background and the viewing duration of the inducing image increased the lightness and chroma of observer’s afterimages. The switch visual afterimage is explained in the context of pertinent visual afterimage literature, and the implications of the current findings are discussed