Ss wore prisms as they reached for a visible target with one hand. When the reaching hand was viewed continuously, aftereffects were restricted to that hand. When the reaching hand was viewed only after each reaching movement had already been completed, aftereffects were obtained with both hands. These findings dispute the generality of assertions that the aftereffects of wearing prisms are exclusively a result of either changes in the sensed position of the prismatically viewed arm or changes in the judgment of the direction of the gaze. Rather, both appear to be possible mechanisms underlying the aftereffects, and their relative prominence depends strongly upon visual feedback conditions.

Each of 12 subjects set a binocularly viewed target to apparent eye level; the target was projected on the rear wall of an open box, the floor of which was horizontal or pitched up and down at angles of 7.5 degrees and 15 degrees. Settings of the target were systematically biased by 60% of the pitch angle when the interior of the box was illuminated, but by only 5% when the interior of the box was darkened. Within-subjects variability of the settings was less under illuminated viewing conditions than in the dark, but was independent of box pitch angle. In a second experiment, 11 subjects were tested with an illuminated pitched box, yielding biases of 53% and 49% for binocular and monocular viewing conditions, respectively. The results are discussed in terms of individual and interactive effects of optical, gravitational, and extraretinal eye-position information in determining judgements of eye level.

Each of nine Ss experienced gravitational-inertial forces (GIFs) of 1.00, 1.25,1.50, and 1.75 G z with his head erect and pitched forward at angles of IS and 30 deg. The magnitude of the elevator illusion was shown to depend on both the intensity of the GlFs and the orientation of the head. Contributions of otolith organ activity and of neck proprioception to the illusion were examined, and theoretical bases for their influences were discussed.Stationary visible objects appear to rise when gravitational-inertial forces (GIFs) are increased in magnitude along an O's head-to-foot, or G z , body axis (

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