Here's the parts list for that model: http://www.kitchenaid.com/digitalassets/MLPDF/Repair%20Part%20List%20-%20W10920582.pdf

I don't see anything in between the left elements.

Thanks. I am not sure how useful it is to have the "bridge" if the middle part won't heat.

If those are the facts, there isn't any. It's just a marking to show you which two elements you can use in tandem. Most induction surfaces allow you to span paired elements without marking them. It's probably an indication that you shouldn't span the other pair.

Will the middle part heat up from the heat generated by the two outer burners? Or will the middle stay cool? Any idea?

You mean the middle part of the burner spanning pan, right? Depends mostly on the burner-spanning pan that you choose. With stoves other than induction ranges, many people find thick aluminum griddles work well. That, of course, will be of no help with an induction range like the KA slide-in you asked about.

There are some induction suitable griddles like this Demeyere one which are designed and built of materials that optimize heat spread and evenness to the point that the absence of a true bridging element does not really matter. Gardenweb/Houzz has had a couple of discussions of them here recently and there is a long one over on chowhound from last fall if the Demeyere interests you.

But plain carbon steel (as with the Chef King griddles) and cast iron (as with the griddles made by Lodge) --- well, not so great for evenly heating the middles. Basically, the materials (carbon steel and cast iron) do not spread heat well and evenly, so they tend to have hotter spots over the burners and less hot in between. That's not just induction, btw, but applies to spanning any two burners without a bridging element between them. If you have the patience for the long preheat, you can cook pancakes over the middle and and even do some teppanyaki style stir frying/ In my experience, the Lodge cast iron griddle took a really long time to preheat and the middle was still somewhat less hot than the areas directly above the burners. Pancakes on the middle took about half again longer to brown than the ones directly above the burners. IME, the Chef King (carbon steel) are more heavily built so a long and slow pre-heat can eventually mitigate the hotspotting.

With roasting pans --- well, again, it depends. If you are using them with a lot of lquid (as for, say, poaching a salmon), the amount of liquid obviates concern about hot spotting. But for reducing sauces or making gravy with pan drippings, there are likely going to be problems with evenness over the middle. You stir a lot, maybe. Also, pan construction makes a big difference, too. Plain steel roasters are often thin which makes them more prone to hot spotting. (Never had much luck with burner-spanning when using thin-walled steel roasters like those from Graniteware.) Heavier clad roasting pans -- theoretically, they could do a pretty good job because the internal layer of aluminum should help spread the heat and even it out. FWIW, I have had great luck using my Demeyere plancha/girddle as a roasting pan as well as a griddle. But I do not have any first hand experience with any other clad roasting pans that were induction capable. Maybe somebody else can speak to that?

Thanks jwvideo! That is helpful. I haven't bought the range yet but am leaning toward induction. I will look for the threads on Demeyere.