The coffee chain is giving all its US staff "unconscious bias" training after protests against the treatment of black customers at some of its stores.

But how do such courses identify biases, and then try to change behaviour? We went to a training session for charity workers held in Richmond, Virginia, to find out.

Video by Rajini Vaidyanathan, Silvia Costeloe, Peter Murtaugh and Arijeta Lajka.