How fast can we adapt

Visual history is well known to affect perception. If one fixates a grating pattern tilted left of the vertical for 30 s, and then looks at a vertical grating, the vertical lines usually appear slightly tilted to the right. This classical visual illusion known as the tilt after-effect was used among many other erroneous representations of the external environment to explore the mechanisms of perception. At the neuronal level, repeated or prolonged exposure to a stimulus (adaptation) is classically known to reduce neurones' responsiveness to the same stimulus. This effect can last from a few seconds to several minutes. While adaptation is associated with perceptual mistakes such as visual illusions, it also often correlates with improved stimulus discrimination and a broadening of the perceptual range. Even though adaptation has been extensively studied, we are still a long way from explaining normal visual performance as well as many adaptation-related visual illusions. We discuss here a recent study of adaptation to image speed published in The Journal of Physiology by Hietanen et al. (2007) that furthers the understanding of adaptation in the visual system.