The effect of expectations on slow oculomotor control—III. Guessing unpredictable target displacements

Abstract

Previously, we had shown that expectations about the direction of future target motion produce involuntary anticipatory smooth eye movements in the direction of the expected target motion ( Kowler and Steinman, 1979, b). The present experiments extend these results to expected target motions in unpredictable directions. Subjects showed anticipatory smooth eye movements while tracking an unfamiliar pattern of right and left-going target steps while they were guessing the direction of the expected steps. Eye velocity increased when subjects became certain that they knew what the pattern was. Guesses also produced anticipatory smooth eye movements for both expected target steps and ramps in one of 12 unknown directions. Anticipatory smooth eye movements produced by guesses and by certain knowledge of target direction were not affected when subjects performed a distracting task (mental arithmetic). These results show that the effect of expectations on slow eye movements cannot be removed simply by making target motions unpredictable. Models of the slow oculomotor subsystems, to be complete, require development of techniques to predict the direction and certainty of human expectations about unpredictable patterns of target motion. A technique, which may serve this purpose, is described.