Spacing effect is a greater memory increase in a review that comes later in time (as long as it does not result in forgetting).
Spacing effect has positive and negative interpretations leading to a degree of confusion:
- positive interpretation: if we increase intervals in learning (to a degree), we can improve learning (i.e. spacing effect is helpful)
- negative interpretation: if we review too often, the results of the review will be ignored by the memory system (i.e. spacing effect is harmful)
In the two component model of memory, we use a stability increase function, which resolves the above confusion by stating that each individual memory trace has an optimum review time that maximizes the expected memory effect, which is a resultant of the spacing effect and the probability of forgetting.