Abstract
Prisms laterally shifting the perceived visual world cause arm movements to deviate from intended targets. The resulting error—the direct effect—both for pointing and throwing movements, usually corresponds to only around half of the prism’s optical power due to an “immediate correction effect”. We investigated the mechanisms of this immediate correction effect. In three experiments with 73 healthy subjects we find that the immediate correction effect is associated with a head and/or eye rotation. Since these rotations are subconscious they are not taken into account by the participants. These subconscious rotations compensate for a large portion of the prism’s optical effect and change the subjective straight ahead. These movements seem to be induced only in a rich visual environment and hence do not take place in the dark. They correspond to the difference between the direct effect and the optical power of the prisms and seem to cause the immediate correction effect. Hence, eye-hand adaptation only adapts to the prism’s optical power minus unconscious head rotation and hence is much smaller than the optical power of the prisms.
Highlights
Eye-hand coordination is essential for daily interactions with the environment, for example reaching towards an object, using tools, opening the door or grasping for a cup of coffee [1]
Measurements an adaptive interval—that is with prisms onisbut before anyon feedback regarding felt versus seen hand were taken after an adaptive interval—that with prisms but before any feedback regarding felt position
People know that the room has not moved while they put on the prisms, so brains have good reasons to attribute the shift of the visual surround on the retina to an “overlooked” eye or head movement
Summary
Eye-hand coordination is essential for daily interactions with the environment, for example reaching towards an object, using tools, opening the door or grasping for a cup of coffee [1]. This eye-hand coordination relies on one of the most important and complex sensory-motor systems in the human body [2]. Prism glasses shift the visual information in the direction of the prismatic shift [1,7,8] while arm/hand proprioception stays unchanged. The pointing error disappears gradually within a few movements without prisms (readaptation)
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