How to set up the duration of background image (.jpg not htlm) with scale response

I want to set up the duration of background image (.jpg) for 5 second and I need the background image to disappear but remain the scale response bottoms.

What is the easiest way to do this?

Thanks!

Can't do that with a plain jpg. Either has to be HTML with an automatic redirect (let me know if you want help with that--did you see that mentioned in another post?) or you could also do it with an animated gif, where after 5 seconds, the constant image changes to a blank image. That would be easily accomplished with any gif animation software (try a search on download.com for shareware).

I guess another solution would be to enter the item twice in MediaLab--once with the image and once without and then simply assign a duration to the first version. If they respond before the time is up on the first version, then skip them over the imageless version.