How animals scan the visual environment

In man, visual information is taken up in a series of stationary fixations, interspersed with fast “saccadic” movements which shift gaze to a new fixation position, with the eye essentially blind during the move. This strategy, which is common to most animals with good vision, both vertebrate and invertebrate, overcomes the potentially severe problem of motion blur caused by the slow (>10 ms) response time of the photo-receptors. There are, however, animals whose eyes actively scan, taking in information during motion, rather than excluding it as in the fixation/saccade strategy. Examples include certain sea-snails, mantis shrimps and jumping spiders. The latter have a dual visual system-conventional eyes for movement detection, and scanning eyes for feature analysis. The possible advantages of these “alternative” ways of seeing are discussed in relation to artificial vision systems