Memory retrieval means bringing information into consciousness that was previously experienced. Four techniques that researchers use to study memory retrieval are free recall, cued recall, recognition, and relearning. In free recall, people study material and then are asked to report everything they can remember about it. Essay and short-answer exams are examples of free recall. The student studies a topic and then is asked to write an essay or provide a short answer about that material. In cued recall, information is provided at test time that is associated with the learned material, and that information is called a retrieval cue, which is a stimulus that brings previously learned information to consciousness. A fill-in-the-blank test question is an example, since the sentence contains cues linked to the material studied that trigger retrieval. Free recall is the most difficult form of memory retrieval, followed by cued recall.
In recognition testing, people are presented with previously studied material mixed with unstudied material. A multiple-choice exam is an example of recognition testing. The student studies the material and then has to recognize the correct answer from among the choices provided. In relearning, retention is measured in terms of how much faster one learns material that was learned but then forgotten. People often retain or remember more information than they recall, which leads to this faster relearning. Retaking a course is an example of relearning. Typically, the student learns the material faster and with fewer errors the second time around.
Encoding conditions greatly impact memory retrieval. When memories are more easily retrieved in a setting that matches the setting in which original learning took place, it is a phenomenon referred to as context-dependent learning (or the encoding specificity principle). This phenomenon has been demonstrated in countless research studies. For example, in 1973, Canadian psychologist Endel Tulving and Australian psychologist Donald Thomson demonstrated context-dependent learning by having people study lists of word pairs, such as "head-light." At test time, they either saw the same cue ("head-____") or a semantically related one ("dark-____"). Performance was three times better if the cues used at retrieval were the same ones used at encoding.
Anything present at the time learning occurred can serve as contextual cues, including smells, sounds, sights, and the emotional state of the learner. For example, people more easily remember an event that took place in a room if they go back to that room. It is also easier to remember material when the emotional learning context matches the emotional retrieval context. Research suggests this context-dependent effect occurs not just for explicit memory but for implicit memory, as well.Another robust explicit memory phenomenon is the serial position effect (also called the primacy-recency effect), in which there is a tendency to remember more information from the beginning and end of an event than from the middle. This was first discovered by German philosopher Hermann Ebbinghaus in 1885 while studying human memory for word lists. The effect applies to explicit memories as diverse as memory for operas attended over the course of decades and gymnastic floor routines. The serial position effect reflects the impact of two factors—proactive interference and retroactive interference. In proactive interference, there is a tendency of earlier learning to impair memory for information acquired later. In retroactive interference, there is a tendency of later learning to impair memory of information learned earlier. For example, suppose a person were asked to memorize the words hat, chair, vase, frame, bowl, window, candy, stair, and cup. Words that come before bowl can disrupt encoding of that word, as can words that come after. Words in the beginning of the list are better remembered because they have less proactive interference (fewer words precede them). Similarly, words at the end of the list are better remembered because they have less retroactive interference (fewer words follow them). Words in the middle are poorly remembered because they suffer from both proactive and retroactive interference.