Proposal CAH should be revised to incorporate a notion of degree of difficulty corresponding to typological markedness. Typological markedness can be determined independently of any particular language or SLA facts by looking at implication hierarchies. Eckman says he is interested in strong form , namely that any differences would predict difficulty. Note that this is not the only strong form of the CAH see for example Stockwell and Bowen in which a hierarchy of difficulty was proposed. Note, there is no empirical verification of these observations.
English speaker has to learn a rule of devoicing, German speaker nothing.
Those areas of the target language which are different from the native language, but are not more marked than the native language will not be difficult. He says that Korean has no voicing contrast at any place of articulation. This is wrong. The very short lag VOT s are voiced intervocallically. Eckman explains the similarities between L2 and L1 acquisition.