Target modality affects visually guided online control of reaching

The integration of vision and proprioception for estimating the hand's starting location prior to a reach has been shown to depend on the modality of the target towards which the reach is planned. Here we investigated whether the processing of online feedback is also influenced by target modality. Participants made reaching movements to a target that was defined by vision, proprioception, or both, and visual feedback about the unfolding movement was either present or absent. To measure online control we used the variability across trials; we examined the course of this variability for the different target modalities and effector conditions. Our results showed that the rate of decrease in variability in the later part of the movements (an indicator of online control) was minimally influenced by effector vision when participants reached towards a proprioceptive target, whereas the rate of decrease was clearly influenced by effector vision when participants reached towards a visual target. In other words, when participants reached towards a proprioceptively defined target they relied less on visual information about the moving hand than when they reached towards a visually defined target. These results suggest that target modality influences visual processing for online control.