Perceptual inequality between two physically equal constant velocities.

When an object moves with an equal constant velocity before and after passing through a tunnel (or before and after a sudden acceleration--or deceleration--in the central part of its trajectory), the two velocities (the one preceding and the one following the tunnel or the sudden acceleration or deceleration) are perceived as different even if actually physically equal. Four experiments were carried out to underestimation of the second velocity (i.e., the one following the tunnel) when the first one (i.e., the one preceding the tunnel) is low, and an overestimation of the second one when the values of the first velocity are higher. An interpretation of the results is proposed, suggesting that an appearance effect (i.e., an apparent higher velocity at the beginning of the movement) could be for the perceptual inequality between the two physically equal constant velocities.