i've had this problem for a while (i now realize): i have trouble telling how close (or far) something is to me when the object isn't in visual field. specifically, if i'm looking at something it isn't a problem but if someone is walking behind me i can't tell if they are a foot or 10 feet away, for example. similarly, if i'm walking under a low overpass or ceiling i can't tell if it's an inch or 10 inches.

what could this relate to? any thoughts on fixing this?

I don't understand. If you can't see it, how would you be able to tell the distance to it ?

Well how do you prevent from hitting your head against a car frame when you get out, for example? you don't keep looking at it as you get out. you have a sense of space and where that object is in that space.. i seem to lack that...

[Proprioception is the internal sense that tells you where your body parts are without your having to look at them. ]
Proprioception - Google Search
Proprioceptive Dysfunction - Google Search

I see a difference between knowing where the door posts is because you have previously seen it and knowing where something is, say behind you, without having seen it.

I have visual memory and mental imaging limitations. I use to have a photographic memory of my surroundings. I could set something down and be able to know exactly where I put it, even if I had to reach behind to pick it up without looking.

I lost that 16 years ago. I have to purposely observe where things are so I can remember or visualize where they are. What used to be a very natural and subconscious process has become a very conscious and purposeful process.

It sounds to me like you have trouble with your 'mind's eye.' Welcome to the club. It takes time to learn new ways to have a sense of where things are. The only trick I have learned is that this is no longer a subconscious function. I have to put more focus and effort into this.

It almost like a newly blind person saying, "I'm blind. How do I see what I cannot see." They have to use other senses and systems to be aware of their surroundings.

Some of these things might just need a sort of 're-calibration.' The injured brain can lose short cuts and other processes that have been learned over time. To re-calibrate those footsteps behind you, you would need to add a visual understanding to what your ears are hearing. The result would be your brain taking a short cut through the process of " I hear footsteps behind me. Are they 2 feet or ten feet behind me? I'll take a quick side glance and see. ..... Ah, they are ten feet back. I'll try to remember this auditory stimulation so that the next time, I won't have to look."

Many with PCS fail to realize than many of our skills were learned over a 20 year experience with life. If we lose that skill, it may take time to regain it because that skill had been previously learned over 20 years time. It will not take another 20 years but it will take time and even some work-arounds.

I had never lost ANYTHING before Jan 2001. I had such good visual recall that I could always remember where I left something. I could tell if my pocket knife was in my pocket without touching it because I knew the sensation of the weight of my pocket knife or wallet or cell phone.
Since that date, I have lost many things, a valuable pocket KNIFE I had owned and used daily for 20 years, misplaced cell phones, and many more.
I finally gave up and put a lanyard on my cell phone so I can hang it around my neck. I replaced that expensive pocket knife with a cheap one.

Personally, I feel like I had to mourn the loss of that skill. I've worked with hand tools my whole life. Setting a tool down and knowing where I set it was a big part of ME. It's like I lost control of my surroundings. BUT, my visual memory and related skills got hammered by my injury. My doc had never seen somebody with such loss of function.

I would bet that you can relearn these skills. Just learn to focus and be aware rather than depending on subconscious skills.

My best to you.

Thanks Mark: if I understand you correctly, I should attempt to be conscious of where things are around me. That is actually what I'm currently doing. Have you made any attempts to retrain this? It's certainly possible to continue to be attentive but it would be nice to retrain this skill (even if over 20 years). If you have made attempts to retrain, is that what you mean by "hear someone behind me, take a look and notice how 20 feet away sounds vs 2 feet away"?

My mom had eyes in the back of her head...so she said.

that would solve my problems! : )

I use recalibrate as the term but retrain also works.

The function is likely still there. The recalibration is what is needed. You hear the sounds. Your brain just needs to calibrate what a 2 foot away sound is compared to a 10 or 20 foot sound.

What is a good way to do that in your view? To just do various activities with my eyes closed (in a controlled manner obviously) and try to see how far away from objects I am? Then open my eyes, etc.?