Forgetting is the loss or failure of memory. Hermann Ebbinghaus studied the relationship between ease of relearning (called savings) and the time between learning and relearning, which he expressed as a forgetting curve (Figure 1 ). He found that most forgetting occurs during the first nine hours after learning.

Figure 1 The Forgetting Curve

Practice, both massed and distributed over time, also affects relearning forgotten material. Ebbinghaus also found that the more an individual rehearses a list of syllables, the better the syllables are recalled. (And as would be expected, given the primacy and recency effects, syllables near the beginning or end of a list are recalled best.) When graphed, the effect of practice results in a U-shaped curve.

Measures of retention. Memories may be retrieved in three ways.

• recall: remembering of previously learned information

  • free recall: recall of items in any order

  • serial recall: recall of items in the order in which they were learned

  • paired associate recall: recall of a second item based on a cue supplied by a first item

• recognition: identification of previously learned information (as, for example from a number of answer choices in a multiple-choice test)

• reconstruction: rebuilding of a scenario from certain remembered details

• Decay is loss of information from memory as a consequence of die passage of time and lack of use. It has been suggested that memory is stored in memory traces, which disappear when not used for a long time.

• Interference is the confusion of one piece of information with another or the suppression of one in favor of another that was processed about the same time (as might happen, for example, if a student takes a Spanish lesson one period and a French lesson the next).

  • Proactive interference occurs if previously learned material interferes with learning of new material.

  • Retroactive interference occurs if learning of new material interferes with the ability to recall previously learned material.

• Amnesia is the inability to remember events from the past because of a psychological trauma ( psychogenic amnesia) or a physiological trauma ( organic amnesia), such as brain damage resulting from a blow to the head. The memory loss is usually limited to a specific period.

  • Retrograde amnesia is the inability to remember happenings that preceded the traumatic event producing the amnesia.

  • Anterograde amnesia is the inability to remember happenings that occur after a traumatic event.

• People sometimes forget things because they find them too unpleasant to think about. Such an occurrence is called motivated forgetting. Sigmund Freud attributed many memory failures, particularly involving painful childhood experiences, to repression (the process of keeping disturbing thoughts or feelings relegated to the unconscious). The repressed material can sometimes be recalled through free association or hypnosis. The recovery of supposedly repressed memories, such as those of childhood sexual abuse, is controversial. Some psychologists, such as Elizabeth Loftus, have called some of the recovered information false memories and suggested that sometimes such information has been implanted by the client's therapist.

Eyewitness testimony. Eyewitness testimony is the courtroom recall of a real-life situation. Studies have shown that eyewitnesses sometimes recall events incorrectly or identify the wrong people. In addition, memories may be embellished after the fact, particularly if a person has a stake in the outcome, but although the memories seemingly improve with time, they may be less rather than more accurate. The reliability of such embellished memories is controversial as is the use of hypnosis to improve memory retrieval.

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