Effect of achromatic afterimage on spatial chromatic induction

摘要

It is known that visual stimuli with luminance contrasts produce afterimages of opposite contrast following adaptation. A bright figure on a dark surround gives an afterimage of a dark figure on a bright surround. However, the exact nature of these afterimages is unclear -- does the visual system treat them the same as it does luminance contrasts from real light? We used spatial chromatic induction to explore this question. Spatial induction occurs when a colored surround induces its complement into a figure. This effect is maximized at equal brightness, and is eliminated when there are high-contrast edges between the figure and ground. Could brightness contrast from an afterimage be used to cancel the luminance contrast in a test display, thereby producing equiluminant conditions and restoring spatial chromatic induction? We used neon color spreading stimuli (grids of colored lines over achromatic backgrounds) to allow for fine control of luminance independent of hue - the luminances of the backgrounds can be manipulated separately from the grids themselves, which provide chromaticity. Participants were presented with a test stimulus which showed little chromatic spatial induction due to luminance contrast between the figure and background. This stimulus was then alternated with an adaptation stimulus which moved from uniform gray to a maximum contrast, under participantsa?? control via a knob. Participants were instructed to find the adaptation stimulus which resulted in the strongest perception of hue within the figure region of the test stimulus. Results suggest that the afterimage integrated with the test stimulus, reducing the edge contrast and enhancing spatial chromatic induction. This would indicate that the integration of an afterimage with real light precedes the neural computations that determine the strength of color induction. This method also offers a potential way to quantify the luminance contrast in an afterimage.