Individual differences in native and non-native speech perception

Sebastian, N.

“Gilead then cut Ephraim off from the fords of the Jordan, and whenever Ephraimite fugitives said, 'Let me cross,' the men of Gilead would ask, 'Are you an Ephraimite?' If he said, 'No,' they then said, 'Very well, say Shibboleth.' If anyone said, 'Sibboleth', because he could not pronounce it, then they would seize him and kill him by the fords of the Jordan. Forty-two thousand Ephraimites fell on this occasion.”

The Bible tells us that 42,000 Ephraimites did not pass the fatal language-test. But presumably, some Ephraimites escaped their fatal fate by properly pronouncing the test-word. Why was it so difficult for some of them to say Shiboleth? Why was it not for others?
While listeners perceive their first language in a fairly automatic manner, with a high efficiency and, seemingly, low computational cost, many (if not most) human beings (like the poor Ephraimites) face enormous challenges to perceive a foreign language, especially if learned late in life. A crucial difference between native and non-native speech perception is that the ultimate L2 performance level shows great variability even in the case of early acquisition. Why is it so difficult to learn a new language? It should not be so complicated, as babies manage to do so effortlessly and in a very short period of time. In the present talk I review some proposals and advance some hypotheses concerning the origin of these individual differences.