Trace decay vs. interference.
There are two schools of thinking regarding the cause of forgetting. The first, trace decay, came out of Ebbinghaus’s work. He showed that time was the primary cause of a loss of memory.
There have been other approaches to the question of memory and forgetting. Scientists such as F. C. Barlett used stories instead of word lists to look at the effect time had on memory. He would have subjects read brief stories and then test their recollection of those stories at various time intervals up to 6 months. Though Barlett initially set out his work as a criticism of Ebbinghaus , especially in his use of non-sense syllables; Barlett’s work showed similar types and degrees of memory loss as could be explained in Ebbinghaus’s work.
Another explanation for forgetting was developed in later years and that is the “interference theory”. Briefly, it states that material learned both before and after the target material interferes with the retention of the designated material. A typical example of this type of study would be the following: 3 groups of subjects, one learns the paired group of words A-B and C-D (car – dog and tree – road). The second learns A-B and A-C, and the third would learn just A-B. The groups would then be tested on their ability to accurately recall the various lists. The results typically were the A-B only group would do the best. The A-B and C-D group would do noticeably worse on their A-B list as well as their C-D lists. The A-B and A-C group though would do the worst over all. They would intermix their two lists. This is not unlike the problems we often encountered in repetitive sections in music where the repeated sections have slight variations. It is a common problem to intermix the sections, ultimately having trouble extracting one’s self from the section.