I would consider having his eyes checked. You would not necessarily know it if he were going blind, particularly if he has lived in the same home for a time and you are not in the habit of moving the furniture because just about any blind dog can "map" his territory and Jack Russell's are very smart and can do so very quickly.
I just had a temporarily totally blind 3 month old JRT puppy map out my place in hours. (He had corneal ulcers and 3rd eyelid stitched shut on both eyes to attempt healing, which worked and his sight is now mostly restored.)
Taking your dog to a different environment can also answer this question. He will either bump into things or refuse to explore at all or very slowly. Of Course, this very likely could not be your problem. The other answer you received before mine, is just as likely.
Good Luck!
Nannette Lewis
Dec 22, 2013 Rating
Jack Russell staring at walls by: William
Since your Jack is getting a little older, I'm wondering if he has some dementia. Our Jack would just walk around our house for hours and then would stand still and stare into space. It was hard to watch. The best thing to do is to distract your dog by walks and toys - like a Kong filled with peanut butter and biscuits. This will leave your Jack less time to stare at the wall - but keep in mind he may still do this a bit. Because your Jack is getting older and this is new behavior, it couldn't hurt to get him checked out by a vet to make sure there isn't any illness causing this.