Prism Adaptation

In normal subjects, flexibility of transformation from retinotopic to body-centered coordinates has been demonstrated by prism adaptation. When subjects view objects through laterally shifting prisms and try to reach for them, their hands will move toward the shifted location and miss the actual object. Subjects will see their hand deviating from the object's apparent location even further to the side of prism shift. After some trials, however, the direction of movement will adapt to the visual distortion. Subjects will reach the actual object while seeing their hand reaching its apparently shifted location. The actual movement path of the hand thus deviates from its visually perceived movement path in the opposite direction of prism shift. Consequently, when prisms are removed subjects will initially misreach in this direction. Prism adaptation and aftereffects are restricted to the hand that performed the movements. This means that rescaling affects the transformation from a retinal to a one-limb-centered rather than globally body-centered reference frame.

Prism shift creates several conflicts. First, the visual location of the hand deviates from its proprioceptive location. Second, the visual path of the reaching hand deviates from the intended path. Third, after mis-reaching the visual location of the hand deviates from the visual location of the object. The motor system could use either of these discrepancies for computing the reaching error and rescaling visuomotor transformation. Subjects' introspections, however, accuse a nonexistent discrepancy between intended movement and proprioceptively signaled movement path of the hand as being the source of errors. They report that their movements aimed at the visually perceived target but were mysteriously pulled to the side of prism shift. At the end of the movement they believed their hands were where they saw them—that is, shifted to the prism-distorted locations. In fact, the hand had faithfully followed the intended path, but vision was distorted. I discuss the phenomenon of visual capture later, but retain now that subjects entertain false beliefs about the perceptual basis of coordinate tranformation rescaling. The brain mechanisms of coordinate transformation seem to work outside the realm of conscious body perception.

Understanding And Treating Autism

Understanding And Treating Autism

Whenever a doctor informs the parents that their child is suffering with Autism, the first & foremost question that is thrown over him is - How did it happen? How did my child get this disease? Well, there is no definite answer to what are the exact causes of Autism.

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