Imagine you are on a trip throughout South America. You speak Spanish pretty well, but have a hard time understanding Portuguese. However, as you reach the border of Colombia and begin to cross into Brazil, you realize that you are still able to understand many of the native speakers better than you expected. What linguistic phenomenon are you experiencing?

Contrastive linguistics.

Explanation:

The contrastive languistics can be understood as a branch of study of the linguistics of comparison between different languages. Through this approach it is possible to describe what are the similarities and differences between a pair of languages. This is the phenomenon found in this question, because the Spanish and Portuguese languages are very close, it is possible to understand the central messages of the two languages using their native language. This is a phenomenon of study of contrastive linguistics.