Effect of spatial attention on anatomical and external reference frames in tactile localization.

This study examined whether spatial attention contributes to anatomical and external reference frames for tactile localization during reaching movements. Nineteen right-handed participants reached toward a target in the left or right spatial hemifield with the left or right index finger. During the reach, a tactile stimulus was delivered to the reaching hand. After reaching, participants repositioned the stimulated hand to the location where the tactile stimulus had been delivered. They then verbally reported the perceived location of the tactile stimulus on the hand. The error in the anatomical reference frame for the left hand showed a more distal deviation than that for the right hand when participants reached into the left spatial hemifield, whereas no such difference was observed when they reached into the right spatial hemifield. This finding suggests that spatial attention in the left hemisphere reduces the proximal deviation of the perceived tactile stimulus location on the right hand within the anatomical reference frame. In the external reference frame, the error for the right hand showed a distal deviation relative to the left hand when they reached toward a target in the left spatial hemifield. Conversely, the error for the left hand showed a distal deviation relative to the right hand when they reached toward a target in the right spatial hemifield. These results indicate that conflict between the anatomical and external reference frames weakens the influence of spatial attention, resulting in a distal bias in perceived tactile location in external space.