Inhibition of Reach Plan on Goal Object Offset

Inhibition of Reach Plan on Goal Object Offset Lari Vainio (lari.vainio@plymouth.ac.uk) School of Psychology, University Of Plymouth, Plymouth, PL4 8AA, UK Rob Ellis (rellis@plymouth.ac.uk) School of Psychology, University Of Plymouth, Plymouth, PL4 8AA, UK Mike Tucker (M.R.Tucker-1@plymouth.ac.uk) School of Psychology, University Of Plymouth, Plymouth, PL4 8AA, UK or left hand button-press response to indicate whether the graspable (everyday household) object was upright or inverted. The objects were displayed in the orientations that were compatible with a right-hand grasp or with a left-hand grasp. The object orientation was observed to facilitate responses of the hand most suited to perform a reach-and- grasp action on the object. This robust effect which has been replicated in several laboratories (e.g. Grezes and Decety, 2002; Phillips and Ward, 2002), demonstrates that when viewing an object the action that it evokes appears to be activated independently of a persons’ intention to act. For convenience, we shall call this observation “the object- orientation effect”. The object-orientation effect can be triggered by an orientation of viewed (novel) cylinders and an orientation of familiar mugs (Vainio, Ellis and Tucker, in press). The object affordance effect can be observed with semantic information (i.e. names of objects) and purely visual information (i.e. size of novel objects) of an object (Tucker and Ellis, 2004; Vainio, Ellis, Tucker and Symes, in press). Intuitively it may be assumed that object orientation can also be derived from different object properties for generating the object-orientation effect. The angle of an object’s primary axis of elongation (visual affordance) or a handle of an object (visual-semantic affordance) can both offer orientation information. In the case of visual-semantic affordance, an object needs to be processed at the semantic level in order to extract affordance information. How we grasp a familiar object and how we use it effectively are profoundly related to each other. Objects that have functional handle are usually picked up by their handles. However, the object is rarely picked up by the handle if individual is interfered with semantic task while he is picking up the object (Creem and Proffitt, 2001). In addition, research has shown that familiar objects with handles, but not familiar objects without handles or unfamiliar objects with handles, activate multiple motor schemata based on semantic, pragmatic and associative components (Sugio, Ogawa & Inui, 2003). Functional properties of an object that are associated with its handle are taken into account during transformation to motor program (Petit, Pegna, Harris & Michel, 2006). Therefore, we have evidence to claim that the object- orientation effect that is elicited by the location of a handle of a mug involves at least some minimal semantic Abstract Previous research has shown that object’s orientation facilitates responses of the hand that is compatible with the orientation. We explored how this object-orientation effect couples with reach planning and control. Experiment 1 used left-right orientated cylinders as stimuli. The orientation of these cylinders was observed to lead to more accurate responses of the orientation compatible hand. When the object disappeared on reach initiation, the reaching of the orientation compatible hand was inhibited. Experiment 2 replicated Experiment 1 with left-right orientated mugs. These objects evoked the typical object-orientation effect in reaction times and accuracy but reach control was not affected. This study suggests that a sudden interruption in the transmission of visual inputs for updating the motor program leads to inhibition of the program. However, this motor control effect depends on whether the motor plan is extracted from visual or visual-semantic object affordance. Keywords: motor control, motor planning, inhibition, visual representation Introduction The visuomotor system has to extract information from the visual array that is relevant for guiding current actions such as reaching to grasp a branch. Similarly, it is important that an organism respond rapidly to sudden changes in its environment. For instance, the motor program for the reach- to-grasp has to be quickly inhibited if the branch moves away from its current position during the reach. Behavioural studies have shown that a viewed graspable object automatically activates a motor program associated with an object’s affordance (i.e. action-relevant attributes of objects) even when this information is irrelevant to the current task demands (e.g. Craighero, Fadiga, Rizzolatti, & Umilta, 1999; Tucker and Ellis, 2001). In affordance effects, the action relevant object attribute is automatically extracted from the visual array to facilitate the motor program, which would be required for the accurate reach-to-grasp action to the object. This interplay between object affordances and motor programming has been extensively examined and evaluated (e.g. Grezes, Tucker, Armony, Ellis, & Passingham, 2003; Fagg & Arbib, 1998). Of most interest is the study presented by Tucker and Ellis (1998). In their study, participants had to make a right