Gravity bias in the interpretation of biological motion by inexperienced chicks

Our ability to recognise biological motion in point-light displays is reduced when the animation sequence is upside-down, taken as evidence that past experience about direction of gravity influences the perception of biological motion. We exposed newly hatched chicks, reared in darkness and thus in the absence of previous visual experience, to point-light animation sequences of a walking hen either upright or upside-down: they responded by aligning their bodies in the apparent direction of motion in the former situation, but not in the latter, indicating that the vertebrate brain might be predisposed to make assumptions about direction of gravity.