Abstract
We investigate how the immediate correction effect decreases mispointing under prisms. Subjects performed rhythmic pointing movements under different conditions with horizontally shifting prisms. Even the first (initial) pointing error is much smaller than the prismatic shift, a phenomenon called the immediate correction effect. Knowledge about the structure of the room and of objects in the room obtained before the prisms were worn may limit the amount of the prismatic displacement perceived. We therefore compared the direct prism effect as well as prismatic adaptation with room illumination switched on versus switched off. Our 44 subjects participated in two experiments, with varying amounts of information about room structure available. The results show a direct effect corresponding to the optical power of the prisms in the dark condition, when in addition body position was slightly rotated in direction of the prismatic shift. But even in the dark, a significant immediate correction effect arises with the fixed body position. The largest immediate correction amounting to almost half of optical displacement arose in the standard condition of bright light and fixed body position.
Highlights
In daily life, we execute many directed movements like grasping a comb, opening the door, or pointing toward an object
A large initial pointing error in direction of the prismatic shift emerges under both conditions
In line with earlier studies (Melamed, Beckett, & Wallace, 1978; Rock, Goldberg, & Mack, 1966), we find that the direct prism effect, that is the deviation of the first pointing movement toward a visual target, is influenced by illumination level
Summary
We execute many directed movements like grasping a comb, opening the door, or pointing toward an object. Coordination system quasiautomatically adjusts to changes (Guan & Wade, 2000), for example, when wearing ordinary or prism glasses (Baraduc & Wolpert, 2002; Taub & Goldberg, 1973). A prism displacing the visual field horizontally induces arm movements that initially miss the target laterally (direct effect; Guan & Wade, 2000; Harris, 1965). After removing the prism glasses, participants initially miss the object in the direction opposite to the prism effect (aftereffect; Guan & Wade, 2000; Harris, 1965; Redding, Rossetti, & Wallace, 2005; Redding & Wallace, 2006). The mispointing decreases gradually by repeated movements and vanishes completely
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