Word meaning acquisition is reflected in brain potentials of isolated words.

Learning a new concept and corresponding word typically involves repeated exposure to the word in the same or a similar context until the link crystallizes in long term memory. Although electrophysiological indices of the result of learning are well documented, there is currently no measure of the process of conceptually-mediated learning itself. Here, we recorded event-related brain potentials from participants who read unfamiliar words presented in isolation followed by a definition that either explained the meaning of the word or was a true, but uninformative statement. Self-reported word knowledge ratings increased for those words that were followed by meaningful definitions and were correlated with a decrease in ERP amplitude of a late frontal negativity (LFN) elicited by the isolated word. Importantly, the rate of LFN amplitude change predicted post-hoc learning outcome measures. Therefore, the LFN is real-time measure that is not under conscious control and which reflects conceptually-mediated learning. We propose that the LFN provides for the first time the opportunity to assess learning during study.