1) Similarities or differences in the languages being learned. If all languages being learned are similar in structure then it would be easier for the simultaneous multilingual because the rules would be similar and there would be less confusion. For the successive multilingual the primary language would have a minor influence in affecting subsequent languages. Neural organisation: since all languages were learned within the critical period we would assume that similar neural structures would be activated regardless of language or sequence of language acquisition. Different tasks however would activate different neural regions, but we would see the same populations activated in a similar task whether the individual was a simultaneous or successive multilingual. Language interference: a simultaneous multilingual is at a higher risk for confusing the languages learned at the same time. This is because early in development there is a steep learning curve for a new language and proper organisation of the rules pertaining to a particular language can get mixed up if many languages are learned simultaneously. A successive multilingual is less at risk because they learn different languages successfully, therefore the structure of one language is developed before establishing a new language structure. The simultaneous bilingual is more likely to develop one structure to accommodate all the learned languages since they are acquired simultaneously.