Abstract
There has long been speculation that the M-cell pathway may be preferentially involved in the processing of the moving stimulus in the flash-lag illusion (Khurana & Nijhawan, 1995; Nijhawan, 2008). Chappell, Hine, and Hardwick (2002) found that making the flash near-equiluminant with its background increased the illusion magnitude, however, when they made the moving stimulus near-equiluminant there was no significant effect on the illusion. We sought to reduce M-pathway response more effectively by adding luminance noise to an isoluminant display, as this has previously been shown to remove remaining luminance signals from the chromatic motion response (Baker, Boulten, & Mullen, 1998; Mullen, Yoshizawa, & Baker, 2003). By splitting the display we were able to manipulate the equiluminant colour, luminance contrast and the presence of luminance noise independently for the flash and the moving stimulus. We found that making the moving stimulus equiluminant significantly reduced the magnitude of the illusion. In addition, when the flash was defined by luminance contrast and the moving stimulus was equiluminant, a number of participants exhibited a significant flash-lead illusion. Our data strongly support the notion that M-pathway processing of the moving object contributes to the flash-lag illusion.