The three basic memory tasks used to measure forgetting are recall, recognition, and relearning.
Recall is the process of remembering information or retrieving it from memory without any external cues. For example, a researcher might ask a participant to recall a list of words that they have previously heard or seen. The researcher would then measure the amount of words the participant can recall without any cues.
Recognition is the process of recognizing previously encountered information. In this task, the researcher presents a list of words and then presents the same words in a different order. The participant then indicates which words they have previously seen. This task measures the participant's ability to recognize which words they have previously encountered.
Relearning is the process of relearning previously learned information. This task requires the participant to learn some information and then after a period of time, they are asked to learn the same information again. The amount of time it takes the participant to relearn the information is measured. This task measures how quickly the participant can relearn the information and how much of it they can retain.
These three tasks are used to measure forgetting because they provide an indication of how information is retained and forgotten over time. By measuring how quickly the participant can recall, recognize, and relearn information, researchers can get an idea of how well the participant is able to remember and retain information.