help adjusting to indoor riding arena

Question
I bought an OTTB 6 yr gelding and have been working with him for 4 months now. I purchased him from a trainer that bought him off the track and worked with him on W/T basics for about 5 months before that. When working with him in the outdoor arena, he is quiet, listens well, is getting rounder and softer in the poll, and is a pretty quick learner. However now that winter has come, we have to work in the indoor arena. I feel like I have a different horse in the indoor! He only gives me about half his attention and feels hollow and dead to my aids. Trying to canter him in the indoor arena is quite frustrating for both of us. Any tips for helping my normally "good boy" get comfortable in the indoor setting would be most appreciated.

Answer
Is there a lot of noise in there, or does sound carry and echo?  Earplugs might help if so.  Also, a set of blinkers might help to focus him on what he is doing, if he is being a looky loo.

Also, break up your routine with him, maybe do some of the same exercises beginning riders do, serpentines, circles, working across the arena on diagonal rather than just straight down.  Anything to make him wonder what is coming next, instead of same old thing.

Does he get turned out to play is another thing that might help.  

When you say he isn't comfortable though, are you meaning that he is nervous and spooky or more bored and ignoring you.  And is the half attention because of one or the other too?

If it is spooky, it could be he also does not see well in there, even when one is brightly lit?  Still makes strange shadows.

If it is dullard, than change things up, and maybe even play music?  Anything to get him livened up.