quantum mechanics - Wave/particle-duality as result of taking different limits of a QFT

There is an account on dualities in quantum field theories and string theories by Polchinski from last week

http://arxiv.org/abs/1412.5704

At the end of page 4, he writes the wave/particle dichotomy arises from different limits you can take in a quantum field theory.

Which limits are meant here exactly, and can one give a proper example? I assume it might relate to many/few quanta states.