No abstract

The course of adaptation to prism was examined by recording S's localization of (a) an object which was objectively straight ahead and (b) straight ahead. It was found that, as the object of regard changed in apparent position and came to be localized correctly, straight ahead changed concomitantly with it. Mean data for 20 Ss with a 25 diopter prism showed that, of the total change in localization during adaptation to the prism, 71% resulted from a concomitant change in the test stimulus and straight ahead, while only 29% could be attributed to a reduction in the disparity between the test stimulus and straight ahead.

Adaptation to lateral prismatic displacement was described by von Helmholtz in 1867. 1 Wearing spectacles which contained wedge prisms, he first demonstrated the apparent displacement by looking at objects, then closing his eyes and trying to touch them. He reached incorrectly, the direction of his errorbeingdetermined by the orientation of the prisms. He then found that he could eliminate the error in either of two ways: by reaching repeatedly for objects with eyes closed, or, "more quickly still," by touching the objects several times while watching his hand through the prisms. Having adapted by either of these techniquea, he repeated the initial procedure as a means of demonstrating that adaptation had taken place: "on trying the above experiment again, we shall discover that now we do not miss the objects but feel for them correctly.' , Helmholtz went on to investigate the locus of the adaptive effect. He found that, if he first adapted by doing all of the reaching with his right hand, keeping his left hand out of his field of view, the adaptive effect nevertheless transferred fully to his left hand.

When S looks at a visual target through prisms Adaptation to lateral prismatic displacement was described by von Helmholtz in 1867 .1 Wearing spectacles which contained wedge prisms, he first demonstrated the apparent displacement by looking at objects, then closing his eyes and trying to touch them. He reached incorrectly, the direction of his error being determined by the orientation of the prisms. He then found that he could eliminate the error in either of two ways: by reaching repeatedly for objects with eyes closed, or, "more quickly still," by touching the objects several times while watching his hand through the prisms. Having adapted by either of these techniquea, he repeated the initial procedure as a means of demonstrating that adaptation had taken place: "on trying the above experiment again, we shall discover that now we do not miss the objects but feel for them correctly.' , Helmholtz went on to investigate the locus of the adaptive effect. He found that, if he first adapted by doing all of the reaching with his right hand, keeping his left hand out of his field of view, the adaptive effect nevertheless transferred fully to his left hand.

Prism vergence thresholds were compared under two conditions: (a) in which each subject believed that he was looking at a single object with both eyes; and (b) in which each subject believed that he was looking at two different objects, one seen from each eye. Thresholds were not significantly different under the two conditions. Problem