In Patisambhidamagga, Treatise on Liberation, it is explained that dependend on ones abilities one will be naturally attracted to contemplating or on anicca, or on dukkha or on anatta.
Contemplating anicca is related to strong faculty of faith.
Contemplating dukkha is related to strong faculty of concentration.
Contemplating anatta is related to great wisdom faculty.
Contemplating anatta is the same as contemplating sunnata (also ToL, Patisambhidamagga).
By the way Nanamoli translated anatta as not-self, anicca as impermanence and dukkha as pain.
The effect of those contemplation is that one turns the mind away from the conditioned. Passion in regard to conditioned phenomena and states weaken. If this happens cognizance enters the signless, wishless, emptiness principle.
I think those are names for the unconditioned?
Siebe