Evaluating forgetting curves.

A new method is described for determining the effect of original earning (or any other variable) on forgetting. The major question is, How much forgetting time is required for memory performance to fall from any given level to some lower level? If this time is the same for different degrees of original learning, then forgetting is not affected by degree of original earning. If this time is greater for higher degrees of original earning, then forgetting is slower with higher original learning. Application of the method to a variety of forgetting data indicated that forgetting is slower for higher degrees of original earning. Slamecka nd McElree (1983) performed three experiments o determine how degree of original learning affects forgetting from long-term memory. Subjects learned verbal material to one of two levels of proficiency and were then tested a t a delay interval ranging from 0.0 to 5.0 days. A variety of different kinds of information were tested by free recall, cued recall, and recognition. Very regular data were obtained; the degree of original earning did not interact with delay inter-val. Slamecka nd McElree concluded that forget-ting was independent of degree of original earning. This conclusion follows if forgetting is oper-ationally defined to be the slope of the forgetting function between any two delay intervals. It is not clear, however, that this definition will ultimately prove to be the most useful in illuminating the processes that underlie forgetting. Consider a phys-ical analogy, that of radioactive decay. Imagine two chunks of radioactive material, identical except in size; the smaller chunk weighs 10 units, and the larger chunk weighs 20 units. Suppose the two chunks decay exponentially with identical decay parameters. If the decay parameter is 1.0, then decay functions could be defined as