Visual facilitation around hands: hand proximity attention and handedness

Visual processing is facilitated by spaces near the hand, which is referred to as hand proximity attention. A team at Tohoku University has been studying this mechanism to isolate hand-related effects from top-down attention; proprioceptive information from visual information; and the influence of response action. They used a visual phenomenon called the flash-lag effect (FLE) as an index of attentional modulation. It was faster and more accurate to identify the visual stimuli projected with a mirror onto the location of the palm of the hand than away from it, even when the hand was invisible under the mirror. This showed that the proprioceptive information of a hand contributed to hand proximity attention, regardless of whether the visual system was activated.

Project lead Satoshi Shioiri explained that "since top-down attention was fixed at a location, we concluded that there is a process to facilitate vision around a hand independent from top-down attention." Differences between left handers and right handers, which can help understand handedness variation in the future, were also observed.

Project lead Satoshi Shioiri explained that "since top-down attention was fixed at a location, we concluded that there is a process to facilitate vision around a hand independent from top-down attention." Differences between left handers and right handers, which can help understand handedness variation in the future, were also observed.

The FLE with a hand near (Near condition) was smaller than that with a hand far (Far condition) for both hands, and when the flash was presented at both the left and right visual fields for right handers (Fig. 3 right). The results reveal that the hand-proximity attention uses proprioceptive information of hand location and worked independently from the top-down attention.

When we tested left handers, the results were different. The results suggest that hand proximity attention, if present, is weaker in left handers. The results of EEG measurements are also different between left and right handers. Clear effect of top down attention and little effect of hand proximity attention was found for right handers whereas little effect of top down attention and significant effect of hand proximity attention was found for left handers. These findings suggest that the process of hand proximity attention for left-handers differs from that for right handers and they are possibly important for understanding the cause of handedness variation.