Effects of substrate brightness differences on isopod (Porcellio scaber) turning and turn alternation

Woodlice ran faster in a straight runway when the floor was white than when it was black. When a runway with totally black or white floors (reflecting different levels of light) met up with equal areas of both brightnesses, woodlice turned in the direction of the runway brightness. Normal turn alternation after a forced turn was suppressed by this tendency to continue following the same substrate brightness when it involved moving in the direction of a repeating turn. However, when it involved turning in the direction of an alternating turn, the tendency to follow the same brightness had no effect on alternation.