How can I modify the Posner 1980 experiment?

I have been asked in my lab class to provide a (simple) modification of the Posner (1980) experiment, however I haven’t been able to think of anything since we already did the only thing that I would have wanted to do last year.

For those that are unfamiliar with this experiment, it is an experiment into visual attention. This picture will help explain:

http://psycnet.apa.org/journals/neu/11/4/images/neu_11_4_467_fig1a.gif

The participant’s instructions are to respond as quickly as they see a certain target. There are 3 levels: one (a) where the cue appears in the same location as the target (valid); one (b) where the cue appears in a different location as the target (invalid); and c) where the cue gives no help to the location of the target (neutral). The prediction is that the reaction times would be in this order: valid < neutral < invalid as our attention is drawn to the cue and thus inhibition of return (IOR) prevents us from looking at that spot again.

What I did last year, that I do not wish to repeat, is that we tried to find a certain time for when IOR starts to work.

I am really struggling and cannot think of any modifications that have a proper question behind them. By this I mean a relevent point for further investigation into improving or providing additional insight into this area. Any help is really appreciated.