Long-term memory is the mechanism which enables us to store information and experiences in a lasting fashion, for possible retrieval at some point in the future. This ability to create and retrieve memories is fundamental to all aspects of cognition, and it is crucial to our ability to function properly as human beings. Ebbinghaus was able to demonstrate experimentally that interference did indeed have a significant effect on memory. He showed that memory scores for the learning of one list were considerably reduced by the subsequent learning of a second list, a phenomenon known as retro-active interference. One crucial aspect of the levels of processing theory is that it emphasises the need to carry out extensive processing of incoming information in order to store it in the long-term memory. Previously it had been widely assumed that information could gain entry into the long-term storage memory by merely being repeated or held in consciousness for a period of time.