Here a couple of extracts from chapter 4 of my new book 'Embracing the Wide Sky':
"A recent finding by researchers at the University College London Centre for Human Communication demonstrates that, given the right stimulus, the adult brain can indeed be retrained to accurately acquire the sounds of a second language...In one study Japanese subjects were retrained to hear the difference between r’s and l’s (something that Japanese students of English find especially difficult)...By the end of the 10-week training period the subjects had improved their recognition of the two sounds by an average of 18%."
(From a later section of the chapter:)
"Examples like these suggest to many linguists that certain words are a more natural ‘fit’ than others for the things they describe. A number of experiments over several decades have supported this idea...the German psycholinguist Heinz Wissemann asked a group of subjects to invent words for various sounds. He found that the subjects tended to create words beginning with ‘p’ ‘t’ or ‘k’ for abrupt sounds, and words beginning with ‘s’ or ‘z’ for flowing sounds. In a more recent experiment involving natural language, the linguist Brent Berlin provided English speakers with fish and bird names from the Huambisa language (spoken in Peru). He found that they were able to distinguish the words for fish from those for birds significantly more often than chance, even though Huambisa bears no resemblance to English."