3-DIMENSIONAL COVERT ATTENTIONAL FUNCTIONS IN PARKINSONS-DISEASE SUBJECTS

This study assessed the ability of mildly affected Parkinson's disease (PD) subjects (n=16) to perform attentional cognitive tasks within a three-dimensional object. A hollow cube was displayed on a computer sc reen and the subject was required to respond as quickly as possible to the highlighting of one of the cube angles by pressing the spacebar o f the keyboard. Prior to the appearance of this imperative stimulus, t he same (''valid'' trials) or an alternative (''invalid'' trials) angl e was highlighted. For the invalid trials this meant that the subject oriented attention to the cued angle but, on imperative stimulus appea rance, was unexpectedly required to redirect attention to another angl e, which could be on a different cube face to that which had been cued . For one experimental session the cube was stationary, that is, objec t-centred and viewer-centred coordinates of a cube angle corresponded. For another session, the cube rotated such that the viewer-centred co ordinates of an angle changed between appearance of the cue and appear ance of the stimulus, but the angle's object-centred coordinates remai ned constant. The finding of lower reaction times for the valid than f or the invalid trials, even when the cube was rotating, indicated that PD subjects could operate attention using an object-centred coordinat e system. However, PD subjects showed exaggerated reaction times when the stimulus appeared in a cube face that was opposite to, rather than the same as, that of the invalidly cued angle. It is suggested that t his reflects a dysfunction in the grouping of the structural component s of the whole object at an attentional level.