Can attention be directed voluntarily to an eye?

Previous studies suggested that information indicating which eye received monocular stimulation is not available to consciousness. However, lack of awareness of eye-of-origin does not necessarily preclude subjects' ability to bias the processing of information presented to an eye. In the present experiment, subjects performed a target detection task under dichoptic viewing, using a precuing procedure. The target appeared above or below fixation and was presented to the right or left eye. The ability of subjects to utilize location cue and eye cue was examined. The results indicated that advance knowledge about the location of the to-be-presented stimulus facilitated performance, and invalid information had an inhibitory effect. In contrast, advance knowledge indicating which eye is more likely to yield the target had no effect whatsoever. These findings suggest that humans cannot direct attention voluntarily to an eye.