It's always been very interesting to me the reasons why it was easier for physically living people to get the attention of those stuck in the afterlife than Helpers.  I found a paragraph with a good, concise explanation on this.  It's in Voyage Beyond Doubt, page 53.  Bruce was met by two huge, extremely bright beings who were going to use him as "bait" in getting the attention of people who died in the 1993 earthquake in India. 


"Avoiding staring into extremely bright lights is something I call a human force of habit.  We physically alive humans are subtly influenced by many such habits, and that's part of the reason I could be used as bait.  Without a second thought, we accept things such as gravity, the solidity of matter, and the privacy of our thoughts.  As a result, we tend to act physically human even when we're in a nonphysical environment.  We tend to project these human forces of habit out into nonphysical environments, and that, somehow, makes it easier for the newly deceased to see and hear us.  They evidently pick up on our subconscious projections, making us more familiar and recognizable to them than Helpers who exist in the nonphysical world.