1. A method of second language learning, comprising: a) presenting a lesson of language learning materials on a display to elicit a response from a learner, said materials presented on the display so that the learner is allowed to move his or her eyes freely in response to the displayed materials; b) measuring EEG data of the learner's brain activity from a plurality of electrodes placed on the learner's scalp; c) tracking the learner's eye movements to provide position signals; d) processing the position signals to determine a fixation event on the materials; e) applying a fixation-locked window to the EEG data to generate a time segment of EEG data; f) extracting one or more features from the time segment of EEG data; g) presenting said one or more features to a classifier to generate a fixation-locked cue indicative of whether the learner exhibited a significant cognitive response to the displayed materials; h) identifying the language learning materials associated with the fixation event; i) retrieving from a user model one or more latent traits tested by the language learning materials associated with the fixation event, each said latent trait representing a language learning skill, a state of each said latent trait representing the learner's mastery of that language learning skill; and j) using the fixation-locked cue to update the state of the one or more latent traits in the user model.