ARE NON-RELEVANT OBJECTS REPRESENTED IN WORKING-MEMORY - THE EFFECT OF NONTARGET OBJECTS ON REACH AND GRASP KINEMATICS

The role of visual information and the precise nature of the represent ations used in the control of prehension movements has frequently been studied by having subjects reach for target objects in the absence of visual information. Such manipulations have often been described as p reventing visual feedback; however, they also impose a working memory load not found in prehension movements with normal vision. In this stu dy we examined the relationship between working memory and visuospatia l attention using a prehension task. In this study six healthy, right- handed adult subjects reached for a wooden block under conditions of n ormal vision, or else with their eyes closed having first observed the placement of the target. Furthermore, the role of visuospatial attent ion was examined by studying the effect, on transport and grasp kinema tics, of placing task-irrelevant ''flanker'' objects (a wooden cylinde r) within the visual field on a proportion of trials. Our results clea rly demonstrated that the position of flankers produced clear interfer ence effects on both transport and grasp kinematics. Furthermore, inte rference effects were significantly greater when subjects reached to t he remembered location of the target (i.e., with eyes closed). The fin ding that the position of flanker objects influences both transport an d grasp components of the prehension movement is taken as support for the view that these components may prepare a coordinated movement in w hich both transport and grasp are specifically adapted to the task in hand. The finding that flanker effects occur primarily when reaching t o the remembered location of the target object is interpreted as suppo rting the view that attentional processes do not work efficiently on w orking memory representations.