The Influence of Limb and Target Vision in Target-Directed and Allocentric Pointing Movements

The top-down nature of allocentric spatial representations (i.e., specifying target locations relative to other objects) is thought to render motor output via an offline mode of control. The present experiment tested this hypothesis by providing detailed trajectory analyses of allocentric and target-directed reaching tasks performed with and without concomitant limb vision. Allocentric tasks required reaches to a location defined by the relationship between a target and reference stimulus, whereas target-directed tasks required reaches directly to a target. Target-directed limb visible trials showed the most effective online trajectory amendments compared to their limb occluded counterparts and allocentric limb visible and occluded trials. Accordingly, I propose that target-directed reaches performed with limb vision are supported via ‘fast’ online visuomotor networks. In contrast, I propose that reaching in the absence of limb vision and/or to an allocentrically defined target is mediated via ‘slow’ offline visuoperceptual networks

Response-specific effects in a joint action task: social inhibition of return effects do not emerge when observed and executed actions are different

Although the inhibition of return (IOR) effect is primarily studied when people act individually, IOR is also observed in social environments where a person observes a partner?s response before executing their own response (social or sIOR). Specifically, an observer takes longer to initiate a response to a target at a location that another individual has just responded to than to another location. The present study was conducted to determine if sIOR emerges when two individuals execute different actions?one participant executed keypress responses and the other completed aiming movements to the same set of stimuli. The two conditions in the present experiment were designed to separate the effects of observing a co-actor?s target information from observing their subsequent response. In the Full Vision condition, observers saw both the target stimuli and the response of the partner. In the Partial Vision condition, observers witnessed the response of the partner, but did not see the target stimulus or any other potentially attention capturing event at the target location. It was found that, although sIOR emerged in the Full Vision condition, sIOR did not emerge in the Partial Vision condition. These and other previous findings on the impact of action goal on sIOR are discussed with reference to the potential contributions of attention and action co-representation mechanisms to the sIOR effect