Dear Friend: No doubt you are working on a very important aspect of walking as an exercise. What I feel is that the issue is not so simple as you are apprehending it to be. First of all make certain observations like when somebody comes out for a walk (may be in an University Campus), he or she is only physically doing the exercise, when the mind is somewhere else, (may be listening to some music, or worrying about some problems, etc.) beside the other factors that you have enumerated. Therefore,  which sensory element is going to affect the walker will have to be judged from such a multipronged mind set. Any way I wish you all the best in your investigation.

This is a very interesting question. I am a health researcher and a Qigong instructor and both these disciplines require me to pay attention to my surroundings and behaviors of people. Thus I am observing a lot through out the day. 

With that said, I have to say I have never really tried to label my own sensory experiences during the course of my day.  So for that thanks! 

Now to answer your question, it would have to be driving in rush hour traffic and next to trucks (visual). Besides that it would be walking through large group of students during class changes on campus (mobility).

CT Scan and like wise equipment are valuable in this type of research, if you want to have objective data. Before and After a walk in University area or else where, volunteers should have  a CT scan to observe which parts of the brain are affected to what extent and observe the correlation that part with some sensory limbs.