photoreceptors within the integration time of the receptors, yet usually, no motion blur is experienced. An elegant model for the elimination of motion blur was proposed by Anderson and vanEssen (1987) who suggested that the neuronal representation of the retinal image is shifted on its way to the cortex, in an opposite direction to the motion. Thus, the cortical representation of objects would be stationary at least during short periods of time. I have measured thresholds for two vernier stimuli, moving simultaneously into opposite directions over identical parts of the retina. Motion blur for these stimuli is not stronger than with a single moving stimulus, and thresholds can be below a photoreceptor diameter. This result cannot be easily reconciled with the hypothesis of 'shifter circuits'