Retroactive interference from translation equivalents: implications for first language forgetting.

First language vocabulary is vulnerable to forgetting after massive exposure to a second language. Two possible factors responsible for the forgetting are degree of semantic overlap between concepts in the two languages and amount of second language exposure. In a laboratory simulation of the language forgetting situation, participants received 10 exposures to a list of words in a foreign language, followed by 2, 5, 10, or 15 exposures to a list in a second foreign language. The second list consisted of either translation equivalents or new concepts. Participants were then tested for retention of the first list. More retroactive interference was found for translation equivalents than for new concepts and for higher degrees of exposure to the second list. When retention of the first list was broken down in terms of gains and losses, effects of both similarity of the second list to the first and amount of exposure to the second list were found only for losses--a fact that points to lack of discriminability as one of the underlying causes of forgetting. Overall, the experimental paradigm proved useful for exploring and developing theories about the causes of first language forgetting.