AVOIDANCE BEHAVIOUR TO LIGHT IN THE PROTOZOA TETRAHYMENA: The effect of a gradual versus an abrupt boundary between dark and light

B ergström , S. R. Avoidance behaviour to light in the Protozoa Tetrahymena. The effect of a gradual versus an abrupt boundary between dark and light. Scand. J. Psychol ., 1969, 10 , 81–88.—Samples of Tetrahymena, trained to avoid light, were placed in the dark part of a partially lighted chamber. The frequency of animals entering the lighted part through a gradual and through an abrupt boundary between dark and light was observed. It was found that a gradual boundary was a much more effective obstacle to the animals than an abrupt one.