Effect of spatial attention on mental rotation

Normal right-handed subjects performed a task requiring mental rotation of the letter R, presented in varying angular orientations in the left or right visual fields. They were told to attend to the side indicated prior to each trial by a centrally located arrow, while maintaining visual fixation on the arrow. On 75% of trials (compatible trials) the arrow pointed to the side of the letter, while on 25% (incompatible trials) it pointed to the other side. Although overall RT was shorter on compatible than on incompatible trials, there was no evidence that spatial attention affected mental-rotation rate. However, estimated rate was higher when attention was to the left side of space, consistent with right hemispheric specialization for mental rotation. This effect was especially marked when presentation of the letter was to the right.