These crystals resonate the thought patterns of a soldier after having time to "tune into" the soldier's thought patterns. This allowed BFR pilots to properly pilot BFRs, having the system connect directly to this crystal, and inquire it for reactions that the soldier themselves would often give to that situation.
During the initial process of imprinting on these crystals, many soldiers complained of hearing voices in their heads. However, many of them also went hysterical when a scientist attempted to remove their crystals, afraid to let go of the most positive voice they've had in their head. After all, who agrees with everything you say and think more than yourself?