LIGHTROM: Manually override Slideshow using arrow keys

I'm sure that in LR4 I used to be able to force the slideshow back or forward a frame or so using the arrow keys. In LR5 this functionality seems to have been removed - or at least I cannot get it to work. Which is a great shame, as often when I'm showing someone a slideshow, I want to go back one frame to re-examine the previous shot and there doesn't seem to be a way of doing so